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1.  Structural Basis of Interactions between Human Glutamate Carboxypeptidase II and Its Substrate Analogs 
Journal of molecular biology  2008;376(5):1438-1450.
Human glutamate carboxypeptidase II (GCPII) is involved in neuronal signal transduction and intestinal folate absorption by means of the hydrolysis of its two natural substrates, N-acetyl-aspartyl-glutamate (NAAG) and folyl-poly-γ-glutamates, respectively. During the past years, tremendous efforts have been made towards the structural analysis of GCPII. Crystal structures of GCPII in complex with various ligands have provided insight into the binding of these ligands, particularly to the S1′ site of the enzyme. In this paper, we have extended structural characterization of GCPII to its S1 site by using dipeptide-based inhibitors that interact with both S1 and S1′ sites of the enzyme. To this end, we have determined crystal structures of human GCPII in complex with phosphapeptide analogs of folyl-γ-glutamate, aspartyl-glutamate and γ-glutamyl-glutamate, reined at resolution of 1.50 Å, 1.60 Å and 1.67 Å, respectively. The S1 pocket of GCPII could be accurately defined and analyzed for the first time, and the data indicate the importance of Asn519, Arg463, Arg534, and Arg536 for recognition of the penultimate (i.e., P1) substrate residues. Direct interactions between the positively charged guanidinium groups of Arg534 and Arg536 and a P1 moiety of a substrate/inhibitor provide mechanistic explanation of GCPII preference for acidic dipeptides. Additionally, observed conformational flexibility of the Arg463 and Arg536 side chains likely regulates GCPII affinity towards different inhibitors and modulates GCPII substrate specificity. The biochemical experiments assessing the hydrolysis of several GCPII substrate derivatives modified at the P1 position, also included in this report, further complement and extend conclusions derived from the structural analysis. The data described here form an excellent foundation for the structurally aided design of novel low-molecular weight GCPII inhibitors and imaging agents.
PMCID: PMC2753231  PMID: 18234225
prostate-specific membrane antigen; metallopeptidase; folate hydrolase; NAALADase; phosphapeptide
2.  Structural characterization of P1′-diversified urea-based inhibitors of glutamate carboxypeptidase II 
Urea-based inhibitors of human glutamate carboxypeptidase II (GCPII) have advanced into clinical trials for imaging metastatic prostate cancer. In parallel efforts, agents with increased lipophilicity have been designed and evaluated for targeting GCPII residing within the neuraxis. Here we report the structural and computational characterization of six complexes between GCPII and P1′-diversified urea-based inhibitors that have the C-terminal glutamate replaced by more hydrophobic moieties. The X-ray structures are complemented by quantum mechanics calculations that provide a quantitative insight into the GCPII/inhibitor interactions. These data can be used for the rational design of novel glutamate-free GCPII inhibitors with tailored physicochemical properties.
PMCID: PMC4077459  PMID: 24731280
GCPII; prostate-specific membrane antigen; PSMA; metallopeptidase; X-ray crystallography; structure-based drug design; urea-based inhibitor
3.  Glutamate carboxypeptidase II and folate deficiencies result in reciprocal protection against cognitive and social deficits in mice: implications for neurodevelopmental disorders 
Developmental Neurobiology  2012;72(6):891-905.
Interactions between genetic and environmental risk factors underlie a number of neuropsychiatric disorders, including schizophrenia (SZ) and autism (AD). Due to the complexity and multitude of the genetic and environmental factors attributed to these disorders, recent research strategies focus on elucidating the common molecular pathways through which these multiple risk factors may function. In this study, we examine the combined effects of a haplo-insufficiency of glutamate carboxypeptidase II (GCPII) and dietary folic acid deficiency. In addition to serving as a neuropeptidase, GCPII catalyzes the absorption of folate. GCPII and folate depletion interact within the one-carbon metabolic pathway and/or of modulate the glutamatergic system. Four groups of mice were tested: wildtype, GCPII hypomorphs, and wildtypes and GCPII hypomorphs both fed a folate deficient diet. Due to sex differences in the prevalence of SZ and AD, both male and female mice were assessed on a number of behavioral tasks including locomotor activity, rotorod, social interaction, pre-pulse inhibition, and spatial memory. Wildtype mice of both sexes fed a folic acid deficient diet showed motor coordination impairments and cognitive deficits, while social interactions were decreased only in males. GCPII mutant mice of both sexes also exhibited reduced social propensities. In contrast, all folate-depleted GCPII hypomorphs performed similarly to untreated wildtype mice, suggesting that reduced GCPII expression and folate deficiency are mutually protective. Analyses of folate and neurometabolite levels associated with glutamatergic function suggest several potential mechanisms through which GCPII and folate may be interacting to create this protective effect.
PMCID: PMC3401954  PMID: 22076974
gene-environment interactions; glutamate; glutamate carboxypeptidase II; folate; one-carbon metabolism
4.  Development of a High-Throughput Fluorescence Polarization Assay to Identify Novel Ligands of Glutamate Carboxypeptidase II 
Journal of biomolecular screening  2012;17(8):1030-1040.
Glutamate carboxypeptidase II (GCPII) is an important target for therapeutic and diagnostic interventions aimed at prostate cancer and neurologic disorders. Here we describe the development and optimization of a high-throughput screening (HTS) assay based on fluorescence polarization (FP) that facilitates the identification of novel scaffolds inhibiting GCPII. First, we designed and synthesized a fluorescence probe based on a urea-based inhibitory scaffold covalently linked to a Bodipy TMR fluorophore (TMRGlu). Next, we established and optimized conditions suitable for HTS and evaluated the assay robustness by testing the influence of a variety of physicochemical parameters (e.g., pH, temperature, time) and additives. Using known GCPII inhibitors, the FP assay was shown to be comparable to benchmark assays established in the field. Finally, we evaluated the FP assay by HTS of a 20 000–compound library. The novel assay presented here is robust, highly reproducible (Z′ = 0.82), inexpensive, and suitable for automation, thus providing an excellent platform for HTS of small-molecule libraries targeting GCPII.
PMCID: PMC4112551  PMID: 22751730
fluorescence polarization; high-throughput screening; glutamate carboxypeptidase II; prostate-specific membrane antigen; metallopeptidase
5.  Glutamate Carboxypeptidase II in Diagnosis and Treatment of Neurologic Disorders and Prostate Cancer 
Current Medicinal Chemistry  2012;19(6):856-870.
Glutamate carboxypeptidase II (GCPII) is a membrane-bound binuclear zinc metallopeptidase with the highest expression levels found in the nervous and prostatic tissue. Throughout the nervous system, glia-bound GCPII is intimately involved in the neuron-neuron and neuron-glia signaling via the hydrolysis of N-acetylaspartylglutamate (NAAG), the most abundant mammalian peptidic neurotransmitter. The inhibition of the GCPII-controlled NAAG catabolism has been shown to attenuate neurotoxicity associated with enhanced glutamate transmission and GCPII-specific inhibitors demonstrate efficacy in multiple preclinical models including traumatic brain injury, stroke, neuropathic and inflammatory pain, amyotrophic lateral sclerosis, and schizophrenia. The second major area of pharmacological interventions targeting GCPII focuses on prostate carcinoma; GCPII expression levels are highly increased in androgen-independent and metastatic disease. Consequently, the enzyme serves as a potential target for imaging and therapy. This review offers a summary of GCPII structure, physiological functions in healthy tissues, and its association with various pathologies. The review also outlines the development of GCPII-specific small-molecule compounds and their use in preclinical and clinical settings.
PMCID: PMC3341092  PMID: 22214450
Metalloprotease; prostate-specific membrane antigen; glutamate excitotoxicity; prostate cancer; N-acetylaspartylglutamate
6.  A high-resolution structure of ligand-free human glutamate carboxypeptidase II 
A crystal structure of ligand-free human glutamate carboxypeptidase II refined to 1.65 Å resolution is reported. The structure provides insight into the active-site of the enzyme in its unliganded state.
Human glutamate carboxypeptidase II (GCPII; EC is an established marker for prostate-cancer diagnosis as well as a candidate therapeutic target for the treatment of diverse pathologies that involve glutamatergic transmission. Structural data on GCPII are thus valuable for the design and optimization of GCPII-specific inhibitors and diagnostic probes. The currently available structure of ligand-free GCPII was refined to a resolution of 3.5 Å. This work reports the structure of the protein refined to 1.65 Å resolution, with crystallographic values of R = 0.207 and R free = 0.228. The new structure extends the resolution appreciably and the new model based on this data shows significant differences when compared with the previously published model.
PMCID: PMC2330195  PMID: 17329803
prostate-specific membrane antigens; metallopeptidase; folate hydrolases; NAALADase
7.  Differential expression of metabotropic glutamate receptor 2 and 3 in schizophrenia: a mechanism for antipsychotic drug action? 
The American journal of psychiatry  2009;166(7):812-820.
Preclinical and clinical data implicate the group II metabotropic glutamate receptors (mGluR2 and mGluR3) in the pathophysiology of schizophrenia. Moreover, a recent phase II clinical trial has demonstrated the antipsychotic efficacy of a mGluR2/3 agonist. The current study was designed to distinguish the expression of mGluR2 and mGluR3 receptor protein in schizophrenia and to quantify glutamate carboxypeptidase II (GCPII) in order to explore a role for the metabotropic receptors in schizophrenia therapeutics. GCPII is an enzyme that metabolizes N-acetylaspartylglutamate (NAAG), the only known specific endogenous agonist of mGluR3 in the mammalian brain.
The normal expression levels of mGluR2, mGluR3 and GCPII were determined in 10 regions of the human post mortem brain using specific antibodies. Differences in expression levels of each protein were then examined in the dorsolateral prefrontal (DLPFC), temporal (TC) and motor cortex (MC) in 15 matched cases of schizophrenia and normal controls. Chronic antipsychotic treatment in rodents was conducted to examine the potential effect of antipsychotic drugs on expression of the 3 proteins.
We found a significant increase in GCPII protein and a reduction in mGluR3 protein in the DLPFC in schizophrenia with mGluR2 protein levels unchanged. Chronic antipsychotic treatment in rodents did not influence GCPII or mGluR3 levels.
Increased GCPII expression and low mGluR3 expression in the DLPFC suggest that NAAG-mediated signaling is impaired in this brain region in schizophrenia. Further, these data implicate the mGluR3 receptor in the antipsychotic action of mGluR2/3 agonists.
PMCID: PMC2860261  PMID: 19487395
prefrontal cortex; glutamate carboxypeptidase II; mGluR; psychosis; human postmortem
8.  Dysregulation of Glutamate Carboxypeptidase II in Psychiatric Disease 
Schizophrenia research  2008;99(1-3):324-332.
Experimental evidence is beginning to converge on an important role for dysregulation of glutamate carboxypeptidase II (GCPII) in schizophrenia. The goal of this study was to determine GCPII levels in postmortem brain specimens of patients with schizophrenia, bipolar disorder or unipolar depression and age-matched control subjects. We used N-[N(S)-1,3-dicarboxypropyl]carbamoyl]-S-3-[125I]iodo-l-tyrosine ([125I]DCIT), a high-affinity radioligand for GCPII, to probe for GCPII expression in prefrontal cortex (PFC) and mesial temporal lobe, two brain regions implicated in the pathophysiology of schizophrenia. We found that GCPII levels measured by [125I]DCIT quantitative autoradiography were significantly lower in the PFC and entorhinal cortex in patients with schizophrenia compared to age-matched controls. Patients with bipolar disorder also expressed significantly lower GCPII levels in PFC than controls. The decrease in [125I]DCIT binding in schizophrenia and bipolar disorder remained significant after adjusting for drug abuse. A significant difference in GCPII levels were also observed between schizophrenia relative to bipolar disorder and depressed subjects in the hippocampus-stratum lucidum and between schizophrenia and bipolar in the CA2 region of the hippocampus with bipolar and depressed subjects expressing higher levels of GCPII than subjects with schizophrenia. These differences in hippocampal GCPII levels may implicate differences in the etiologies of these mental disorders. In summary, this study demonstrates a regional dysregulation of GCPII expression in the brain of patients with schizophrenia and other psychiatric disorders and supports a hypoglutamatergic state of the former illness. GCPII may represent a viable therapeutic target for intervention in psychiatric disease. (241 words)
PMCID: PMC2287371  PMID: 18191545
Schizophrenia; bipolar disorder; depression; NAALADase; GCPII - [125I]DCIT, human brain; imaging
9.  NAAG peptidase inhibitors block cognitive deficit induced by MK-801 and motor activation induced by d-amphetamine in animal models of schizophrenia 
Translational Psychiatry  2012;2(7):e145-.
The most widely validated animal models of the positive, negative and cognitive symptoms of schizophrenia involve administration of d-amphetamine or the open channel NMDA receptor blockers, dizocilpine (MK-801), phencyclidine (PCP) and ketamine. The drug ZJ43 potently inhibits glutamate carboxypeptidase II (GCPII), an enzyme that inactivates the peptide transmitter N-acetylaspartylglutamate (NAAG) and reduces positive and negative behaviors induced by PCP in several of these models. NAAG is an agonist at the metabotropic glutamate receptor 3 (mGluR3). Polymorphisms in this receptor have been associated with expression of schizophrenia. This study aimed to determine whether two different NAAG peptidase inhibitors are effective in dopamine models, whether their efficacy was eliminated in GCPII knockout mice and whether the efficacy of these inhibitors extended to MK-801-induced cognitive deficits as assessed using the novel object recognition test. ZJ43 blocked motor activation when given before or after d-amphetamine treatment. (R,S)-2-phosphono-methylpentanedioic acid (2-PMPA), another potent NAAG peptidase inhibitor, also reduced motor activation induced by PCP or d-amphetamine. 2-PMPA was not effective in GCPII knockout mice. ZJ43 and 2-PMPA also blocked MK-801-induced deficits in novel object recognition when given before, but not after, the acquisition trial. The group II mGluR antagonist LY341495 blocked the effects of NAAG peptidase inhibition in these studies. 2-PMPA was more potent than ZJ43 in a test of NAAG peptidase inhibition in vivo. By bridging the dopamine and glutamate theories of schizophrenia with two structurally different NAAG peptidase inhibitors and demonstrating their efficacy in blocking MK-801-induced memory deficits, these data advance the concept that NAAG peptidase inhibition represents a potentially novel antipsychotic therapy.
PMCID: PMC3410622  PMID: 22850437
cognition; d-amphetamine; NAAG; N-acetylaspartylglutamate; PCP; schizophrenia
10.  Localization of NAAG-related gene expression deficits to the anterior hippocampus in schizophrenia 
Schizophrenia research  2009;111(1-3):131-137.
N-acetyl aspartyl glutamate (NAAG) is an endogenous agonist at the metabotropic glutamate receptor 3 (mGluR3,GRM3) receptor and antagonist at the N-methyl D-aspartate (NMDA) receptor, both receptors important to the pathophysiology of schizophrenia. Glutamate carboxypeptidase II (GCPII), an enzyme that metabolizes NAAG, is also implicated in this illness. In this study, we conducted in situ hybridization experiments to examine expression of mGluR3 and GCPII transcripts along the rostrocaudal axis of the human postmortem hippocampus. We hypothesized that we would find changes in mGluR3 and/or GCPII in the AH but not posterior hippocampus (PH) in schizophrenia. We compared mRNA levels of these genes in the dentate gyrus (DG) and cornu ammonis (CA)1 and CA3 of AH and PH in 20 matched pairs of control and schizophrenia cases. In controls, mGluR3 is highly expressed in the DG and at lower levels in CA1 and CA3 while GCP II is expressed at similar levels in these regions. Group comparisons show a significant reduction of GCPII mRNA level in the AH in schizophrenia. Post hoc analyses reveal this difference is localized to the CA1 region. In addition, we find a significant positive correlation between GCPII and mGluR3 mRNA in the CA3 of the control AH (r=0.66,p=0.008) which is not present in schizophrenia (r=0.096,p=0.76). This may reflect a disrupted functional interaction between NAAG and mGluR3 in CA3 in schizophrenia. These data suggest that NAAG-mediated signaling is disrupted in the AH in schizophrenia and localize the defect to the CA1 and CA3 regions.
PMCID: PMC2685203  PMID: 19403271
glutamate; psychosis; post mortem; in situ; GRM3; mGluR3
11.  Combined Impact of Polymorphism of Folate Metabolism Genes; Glutamate Carboxypeptidase, Methylene Tetrahydrofolate Reductase and Methionine Synthase Reductase on Breast Cancer Susceptibility in Kashmiri Women 
Folate and methionine play a crucial role in DNA synthesis, repair and the epigenetic profile of cell. Hence, the alterations in the folate metabolism can lead to aberrant proliferation leading to neoplasia. Most of the studies have associated polymorphisms in methylene tetrahydrofolate reductase (MTHFR) and methionine synthase reductase (MTRR) genes with reduced risk of cervical and colorectal cancer. However, the association with breast cancer is still controversial. Further, the involvement of Glutamate carboxypeptidase II (GCPII) polymorphism in cancer is not known. In the present study, we analyzed if the individual and combined effects of polymorphisms in folate pathway genes viz., MTHFR 677C > T, MTHFR 1298A > C, MTRR 66A > G and GCP II 1561 C>T, have any role in altering the susceptibility to breast cancer.
The DNA of 35 female breast cancer patients and 33 healthy individuals, in the Kashmiri population from India, were analyzed using a PCR-RFLP approach for the above mentioned polymorphisms.
Individuals carrying the MTHFR 677CT/TT and GCPII 1561 CT genotype showed a 3.5 (95% CI: 3.1–3.7, P<0.02) and 7.7 (95% CI: 6.7–9.1, P<0.001) fold decreased risk for breast cancer than the wild types (MTHFR 677CC and GCPII 1561 CC). Subjects with MTRR 66 G-allele showed a 4.5 fold decreased risk (OR: 0.22, 95% CI: 0.20, 0.24, P<0.0005) compared to the wild type (MTRR 66A). Further, subjects with combined polymorphisms in MTHFR, GCPII and MTRR loci revealed a significant reduction of breast cancer risk.
This study indicates (i) a protective role of polymorphisms in MTHFR, GCPII, MTRR against breast cancer in the study subjects, and (ii) combined effect of polymorphisms is more pronounced than single genetic polymorphism, thereby emphasizing the role of gene-gene interaction in the susceptibility to breast cancer.
PMCID: PMC3068715  PMID: 21475466
12.  Bioisosterism of Urea-Based GCPII Inhibitors: Synthesis and Structure-Activity Relationships Studies 
We report a strategy based on bioisosterism to improve the physicochemical properties of existing hydrophilic, urea-based GCPII inhibitors. Comprehensive structure-activity relationship studies of the P1’ site of ZJ-43- and DCIBzL-based compounds identified several glutamate-free inhibitors with Ki values below 20 nM. Among them, compound 32d (Ki = 11 nM) exhibited selective uptake in GCPII-expressing tumors by SPECT-CT imaging in mice. A novel conformational change of amino acids in the S1’ pharmacophore pocket was observed in the X-ray crystal structure of GCPII complexed with 32d.
PMCID: PMC2818328  PMID: 19897367
PSMA; glutamate carboxypeptidase II; molecular imaging; radiopharmaceutical; SPECT
13.  Glutamate carboxypeptidase II (GCPII) inhibitor displays anti-glutamate and anti-cocaine effects in an invertebrate assay 
Amino Acids  2011;42(6):2521-2524.
Glutamate carboxypeptidase II (GCPII) inhibitors are promising anti-glutamatergic and anti-addictive agents. We hypothesized that a GCPII inhibitor 2 (phosphonomethyl)pentanedioic acid (2-PMPA) would display anti-stereotypical activity in planarians. Experiments revealed that 2-PMPA displayed no overt behavioral activity by itself but attenuated stereotypical counts (C-shape hyperkinesias) elicited by four compounds (2-PMPA rank order potency: glutamate > NMDA > pilocarpine > cocaine). These data suggest GCPII inhibitors display broad-spectrum efficacy against behavioral activity produced by glutamatergic and non-glutamatergic compounds in an invertebrate assay.
PMCID: PMC3265618  PMID: 21850438
GCPII; glutamate; 2-PMPA; cocaine; planaria; NMDA; pilocarpine; stereotypy
14.  NAAG Peptidase Inhibitor Improves Motor Function and Reduces Cognitive Dysfunction in a Model of TBI with Secondary Hypoxia 
Brain research  2013;1515:98-107.
Immediately following traumatic brain injury (TBI) and TBI with hypoxia, there is a rapid and pathophysiological increase in extracellular glutamate, subsequent neuronal damage and ultimately diminished motor and cognitive function. N-acetyl-aspartyl glutamate (NAAG), a prevalent neuropeptide in the CNS, is co-released with glutamate, binds the presynaptic mGluR3 (group II metabotropic glutamate receptor) and suppresses glutamate release. However, the catalytic enzyme glutamate carboxypeptidase II (GCPII) rapidly hydrolyzes NAAG into NAA and glutamate. Inhibition of the GCPII enzyme with NAAG peptidase inhibitors reduces the concentration of glutamate both by increasing the duration of NAAG activity on mGluR3 and by reducing degradation into NAA and glutamate resulting in reduced cell death in models of TBI and TBI with hypoxia. In the following study, rats were administered the NAAG peptidase inhibitor PGI-02776 (10 mg/kg) 30 min following TBI combined with a hypoxic second insult. Over the two weeks following injury, PGI-02776 treated rats had significantly improved motor function as measured by increased duration on the rota-rod and a trend toward improved performance on the beam walk. Furthermore, two weeks post-injury, PGI-02776-treated animals had a significant decrease in latency to find the target platform in the Morris water maze as compared to vehicle-treated animals. These findings demonstrate that the application of NAAG peptidase inhibitors can reduce the deleterious motor and cognitive effects of TBI combined with a second hypoxic insult in the weeks following injury.
PMCID: PMC3672358  PMID: 23562458
Traumatic brain injury (TBI); Hypoxia; Excitotoxicity; N-acetylaspartylglutamate (NAAG); Behavior; Pre-clinical
15.  NAAG Peptidase Inhibitor Reduces Cellular Damage in a Model of TBI with Secondary Hypoxia 
Brain research  2012;1469:144-152.
Traumatic brain injury (TBI) leads to a rapid and excessive glutamate elevation in the extracellular milieu, resulting in neuronal degeneration and astrocyte damage. Posttraumatic hypoxia is a clinically relevant secondary insult that increases the magnitude and duration of glutamate release following TBI. N-acetyl-aspartyl glutamate (NAAG), a prevalent neuropeptide in the CNS, suppresses presynaptic glutamate release by its action at the mGluR3 (a group II metabotropic glutamate receptor). However, extracellular NAAG is rapidly converted into NAA and glutamate by the catalytic enzyme glutamate carboxypeptidase II (GCPII) reducing presynaptic inhibition. We previously reported that the GCPII inhibitor ZJ-43 and its prodrug di-ester PGI-02776 reduce the deleterious effects of excessive extracellular glutamate when injected systemically within the first 30 minutes following injury. We now report that PGI-02776 (10 mg/kg) is neuroprotective when administered 30-minutes post-injury in a model of TBI plus 30 minutes of hypoxia (FiO2 = 11%). 24-hrs following TBI with hypoxia, significant increases in neuronal cell death in the CA1, CA2/3, CA3c, hilus and dentate gyrus were observed in the ipsilateral hippocampus. Additionally, there was a significant reduction in the number of astrocytes in the ipsilateral CA1, CA2/3 and in the CA3c/hilus/dentate gyrus. Administration of PGI-02776 immediately following the cessation of hypoxia significantly reduced neuronal and astrocytic cell death across all regions of the hippocampus. These findings indicate that NAAG peptidase inhibitors administered post-injury can significantly reduce the deleterious effects of TBI combined with a secondary hypoxic insult.
PMCID: PMC3424068  PMID: 22750589
Traumatic brain injury (TBI); Hypoxia; Hippocampus; Neuronal degeneration; Glutamate; N-acetylaspartylglutamate (NAAG); astrocyte
16.  δ-Thiolactones as prodrugs of thiol-based glutamate carboxypeptidase II (GCPII) inhibitors 
Journal of medicinal chemistry  2013;57(1):243-247.
δ-Thiolactones derived from thiol-based glutamate carboxypeptidase II (GCPII) inhibitors were evaluated as prodrugs. In rat liver microsomes, 2-(3-mercaptopropyl)pentanedioic acid (2-MPPA, 1) was gradually produced from 3-(2-oxotetrahydro-thiopyran-3-yl)propionic acid (5), a thiolactone derived from 1. Compound 1 was detected in plasma at concentrations well above its IC50 value for GCPII following oral administration of 5 in rats. Consistent with the oral plasma pharmacokinetics, thiolactone 5 exhibited efficacy in a rat model of neuropathic pain following oral administration.
PMCID: PMC3932958  PMID: 24354364
17.  Efficient and versatile one-step affinity purification of in vivo biotinylated proteins: Expression, characterization and structure analysis of recombinant human Glutamate Carboxypeptidase II 
Affinity purification is a useful approach for purification of recombinant proteins. Eukaryotic expression systems have become more frequently used at the expense of prokaryotic systems since they afford recombinant eukaryotic proteins with post-translational modifications similar or identical to the native ones.
Here, we present a one-step affinity purification set-up suitable for the purification of secreted proteins. The set-up is based on the interaction between biotin and mutated streptavidin. Drosophila Schneider 2 cells are chosen as the expression host, and a biotin acceptor peptide is used as an affinity tag. This tag is biotinylated by E. coli biotin-protein ligase in vivo. We determined that localization of the ligase within the ER led to the most effective in vivo biotinylation of the secreted proteins. We optimized a protocol for large-scale expression and purification of AviTEV-tagged recombinant human glutamate carboxypeptidase II (Avi-GCPII) with milligram yields per litre of culture. We also determined the 3D structure of Avi-GCPII by X-ray crystallography and compared the enzymatic characteristics of the protein to those of its non-tagged variant. These experiments confirmed that AviTEV tag does not affect the biophysical properties of its fused partner.
Purification approach, developed here, provides not only a sufficient amount of highly homogenous protein but also specifically and effectively biotinylates a target protein and thus enables its subsequent visualization or immobilization.
PMCID: PMC3443621  PMID: 22178733
affinity purification; biotin acceptor peptide; recombinant protein expression; biotin-protein ligase (BirA); co-localization; PSMA
18.  Immunohistological and electrophysiological evidence that N-acetylaspartylglutamate (NAAG) is a co-transmitter at the vertebrate neuromuscular junction 
Immunohistochemical studies previously revealed the presence of the peptide transmitter N-acetylaspartylglutamate (NAAG) in spinal motor neurons, axons and presumptive neuromuscular junctions (NMJ). At synapses in the CNS, NAAG has been shown to activate the type 3 metabotropic glutamate receptor (mGluR3) and is inactivated by an extracellular peptidase, glutamate carboxypeptidase II (GCPII). The present study tested the hypothesis that NAAG meets the criteria for classification as a cotransmitter at the vertebrate NMJ. Confocal microscopy confirmed the presence of NAAG immunoreactivity and extended the resolution of the peptide's location in the lizard (Anolis carolinensis) NMJ. NAAG was localized to a presynaptic region immediately adjacent to postsynaptic acetylcholine receptors. NAAG was depleted by potassium-induced depolarization and by electrical stimulation of motor axons. The NAAG receptor, mGluR3, was localized to the presynaptic terminal consistent with NAAG's demonstrated role as a regulator of synaptic release at central synapses. In contrast, glutamate receptors, mGluR2 and NMDA, were closely associated with acetylcholine receptors in the postsynaptic membrane. GCPII, the NAAG inactivating enzyme, was identified exclusively in perisynaptic glial cells. This localization was confirmed by the loss of immunoreactivity when these cells were selectively eliminated. Finally, electrophysiological studies showed that exogenous NAAG inhibited evoked neurotransmitter release by activating a group II metabotropic glutamate receptor (mGluR2 or mGluR3). Collectively, these data support the conclusion that NAAG is a co-transmitter at the vertebrate NMJ.
PMCID: PMC3538924  PMID: 23134476
vertebrate neuromuscular junction; N-acetylaspartylglutamate; NAAG; mGluR3; GCPII; NMDA; Anolis carolinensis
19.  GCPII Imaging and Cancer 
Current medicinal chemistry  2012;19(9):1346-1359.
Glutamate carboxypeptidase II (GCPII) in the central nervous system is referred to as the prostate-specific membrane antigen (PSMA) in the periphery. PSMA serves as a target for imaging and treatment of prostate cancer and because of its expression in solid tumor neovasculature has the potential to be used in this regard for other malignancies as well. An overview of GCPII/PSMA in cancer, as well as a discussion of imaging and therapy of prostate cancer using a wide variety of PSMA-targeting agents is provided.
PMCID: PMC4076792  PMID: 22304713
Prostate-specific membrane antigen; PSMA; prostate cancer; molecular imaging; PET; SPECT
20.  Gene–gene interaction in folate-related genes and risk of neural tube defects in a UK population 
Journal of Medical Genetics  2004;41(4):256-260.
Objective: To investigate the contribution of polymorphic variation in genes involved in the folate-dependent homocysteine pathway in the aetiology of neural tube defects (NTD).
Design: Case-control association study.
Subjects: A total of 530 individuals from families affected by NTD, 645 maternal controls, and 602 healthy newborn controls from the northern UK.
Main outcome measures: Seven polymorphisms in six genes coding for proteins in the folate-dependent homocysteine pathway (MTHFR 677C→T, MTHFR 1298A→C, MTRR 66A→G, SHMT 1420C→T, CßS 844ins68, GCPII 1561C→T, RFC-1 80G→A). The impact of each polymorphism and the effect of gene–gene interactions (epistasis) upon risk of NTD were assessed using logistic regression analysis.
Results: The MTHFR 677C→T polymorphism was shown to represent a risk factor in NTD cases (CC v CT+TT odds ratio (OR) 2.03 [95% confidence interval (CI) 1.09, 3.79] p = 0.025) and the MTRR 66A→G polymorphism was shown to exert a protective effect in NTD cases (AA v AG+GG OR 0.31 [95% CI 0.10, 0.94] p = 0.04). When statistical tests for interaction were conducted, three genotype combinations in cases (MTRR/GCPII; MTHFR 677/CßS; MTHFR 677/MTRR) and one combination in case mothers (CßS/RFC-1) were shown to elevate NTD risk. Maternal–fetal interaction was also detected when offspring carried the MTHFR 677C→T variant and mothers carried the MTRR 66A→G variant, resulting in a significantly elevated risk of NTD.
Conclusion: Both independent genetic effects and gene–gene interaction were observed in relation to NTD risk. Multi-locus rather than single locus analysis might be preferable to gain an accurate assessment of genetic susceptibility to NTD.
PMCID: PMC1735724  PMID: 15060097
21.  Moving beyond Rules: The Development of a Central Nervous System Multiparameter Optimization (CNS MPO) Approach To Enable Alignment of Druglike Properties 
ACS Chemical Neuroscience  2010;1(6):435-449.
The interplay among commonly used physicochemical properties in drug design was examined and utilized to create a prospective design tool focused on the alignment of key druglike attributes. Using a set of six physicochemical parameters ((a) lipophilicity, calculated partition coefficient (ClogP); (b) calculated distribution coefficient at pH = 7.4 (ClogD); (c) molecular weight (MW); (d) topological polar surface area (TPSA); (e) number of hydrogen bond donors (HBD); (f) most basic center (pKa)), a druglikeness central nervous system multiparameter optimization (CNS MPO) algorithm was built and applied to a set of marketed CNS drugs (N = 119) and Pfizer CNS candidates (N = 108), as well as to a large diversity set of Pfizer proprietary compounds (N = 11 303). The novel CNS MPO algorithm showed that 74% of marketed CNS drugs displayed a high CNS MPO score (MPO desirability score ≥ 4, using a scale of 0−6), in comparison to 60% of the Pfizer CNS candidates. This analysis suggests that this algorithm could potentially be used to identify compounds with a higher probability of successfully testing hypotheses in the clinic. In addition, a relationship between an increasing CNS MPO score and alignment of key in vitro attributes of drug discovery (favorable permeability, P-glycoprotein (P-gp) efflux, metabolic stability, and safety) was seen in the marketed CNS drug set, the Pfizer candidate set, and the Pfizer proprietary diversity set. The CNS MPO scoring function offers advantages over hard cutoffs or utilization of single parameters to optimize structure−activity relationships (SAR) by expanding medicinal chemistry design space through a holistic assessment approach. Based on six physicochemical properties commonly used by medicinal chemists, the CNS MPO function may be used prospectively at the design stage to accelerate the identification of compounds with increased probability of success.
PMCID: PMC3368654  PMID: 22778837
Multiparameter optimization (MPO); central nervous system (CNS); CNS MPO; CNS drugs; CNS candidates; lipophilicity; topological polar surface area; polarity; molecular weight; hydrogen bond donor; most basic pKa; high-throughput screening; passive permeability; Madin−Darby canine kidney; P-glycoprotein; human liver microsome stability; Unbound intrinsic clearance; drug−drug interactions; dofetilide binding; transformed human liver epithelial cells; cellular toxicity; Harrington optimization; desirability score; multivariant optimization
22.  On Quantitative Relationships Between Drug-Like Compound Lipophilicity and Plasma Free Fraction in Monkey and Human 
Journal of pharmaceutical sciences  2011;101(3):1028-1039.
Drug interactions with plasma proteins influence their pharmacokinetics and pharmacodynamics. We aimed to test whether a strong quantitative relationship exists between plasma free fraction (fP) and lipophilicity for low molecular weight nonacidic drug-like compounds. We measured the n-octanol-buffer distribution coefficients at pH 7.4 (mlogD) of 18 diverse radiotracers (<470 Da) used for brain imaging with positron emission tomography in vivo. Lipophilicities were also computed as clogD with two software packages. The fP values for monkeys and humans were determined by ultrafiltration and transformed into mlogDpr/pl values representing the log10 of the within phase partition of the radiotracers between plasma proteins and remaining plasma. mlogDpr/pl correlated strongly with mlogD for human (mlogDpr/pl = 0.733mlogD−0.780, r2 = 0.74) and monkey (mlogDpr/pl = 0.780mlogD−1.15, r2 = 0.83), but less strongly with clogD. These relationships were significantly different between species (P = 0.006). Removal of eight fluorinated compounds from the datasets raised r2 to 0.81 and 0.91 for humans and monkeys, respectively. For the tested compounds, we conclude that n-octanol-buffer (pH 7.4) distribution strongly models that between plasma proteins and remaining plasma and moreover that mlogD accounts for over 74% of compound mlogDpr/pl and is a strong determinant of fP.
PMCID: PMC3789652  PMID: 22170327
Protein binding; drug-like properties; physicochemical properties; logP; structure-property relationship; lipophilicity; drug; radiotracer; logD; plasma free fraction
23.  An integrated approach to the ligand binding specificity of Neisseria meningitidis M1 alanine aminopeptidase by fluorogenic substrate profiling, inhibitory studies and molecular modeling 
Biochimie  2012;95(2):419-428.
Neisseria meningitides is a gram-negative diplococcus bacterium and is the main causative agent of meningitis and other meningococcal diseases. Alanine aminopeptidase from N. meningitides (NmAPN) belongs to the family of metallo-exopeptidase enzymes, which catalyze the removal of amino acids from the N-terminus of peptides and proteins, and are found among all the kingdoms of life. NmAPN is suggested to be mostly responsible for proteolysis and nutrition delivery, similar to the orthologs from other bacteria.
To explore the possibility of NmAPN being a potential drug target for inhibition and development of novel therapeutic agents, the specificity of the S1 and S1′ binding sites were explored using an integrated approach. Initially, an extensive library consisting of almost 100 fluorogenic substrates derived from both natural and unnatural amino acids, were used to obtain a detailed substrate fingerprint of the S1 pocket of NmAPN. A broad substrate tolerance of NmAPN was revealed, with bulky basic and hydrophobic ligands being the most favored substrates. Additionally, the potency of a set of organophosphorus inhibitors of neutral aminopeptidases, amino acid and dipeptide analogues was determined. Inhibition constants in the nanomolar range, determined for phosphinic dipeptides, proves the positive increase in inhibition impact of the P1′ ligand elongation. The results were further verified via molecular modeling and docking of canonical aminopeptidase phosphinic dipeptide inhibitors in the NmAPN active site. These studies present comprehensive characterization of interactions responsible for specific ligand binding. This knowledge provides invaluable insight into understanding of the enzyme and development of novel NmAPN inhibitors.
PMCID: PMC3557594  PMID: 23131591
M1 aminopeptidase; Neisseria meningitidis; fluorogenic substrates; organophosphorus inhibitors; S1 and S1′ binding sites specificity
24.  Structure-Guided, Single-Point Modifications in the Phosphinic Dipeptide Structure Yield Highly Potent and Selective Inhibitors of Neutral Aminopeptidases 
Journal of Medicinal Chemistry  2014;57(19):8140-8151.
Seven crystal structures of alanyl aminopeptidase from Neisseria meningitides (the etiological agent of meningitis, NmAPN) complexed with organophosphorus compounds were resolved to determine the optimal inhibitor–enzyme interactions. The enantiomeric phosphonic acid analogs of Leu and hPhe, which correspond to the P1 amino acid residues of well-processed substrates, were used to assess the impact of the absolute configuration and the stereospecific hydrogen bond network formed between the aminophosphonate polar head and the active site residues on the binding affinity. For the hPhe analog, an imperfect stereochemical complementarity could be overcome by incorporating an appropriate P1 side chain. The constitution of P1′-extended structures was rationally designed and the lead, phosphinic dipeptide hPhePψ[CH2]Phe, was modified in a single position. Introducing a heteroatom/heteroatom-based fragment to either the P1 or P1′ residue required new synthetic pathways. The compounds in the refined structure were low nanomolar and subnanomolar inhibitors of N. meningitides, porcine and human APNs, and the reference leucine aminopeptidase (LAP). The unnatural phosphinic dipeptide analogs exhibited a high affinity for monozinc APNs associated with a reasonable selectivity versus dizinc LAP. Another set of crystal structures containing the NmAPN dipeptide ligand were used to verify and to confirm the predicted binding modes; furthermore, novel contacts, which were promising for inhibitor development, were identified, including a π–π stacking interaction between a pyridine ring and Tyr372.
PMCID: PMC4331105  PMID: 25192493
25.  Purification and characterization of a developmentally regulated carboxypeptidase from Mucor racemosus. 
Journal of Bacteriology  1992;174(2):447-455.
A developmentally regulated carboxypeptidase was purified from hyphae of the dimorphic fungus Mucor racemosus. The enzyme, designated carboxypeptidase 3 (CP3), has been purified greater than 900-fold to homogeneity and characterized. The carboxypeptidase migrated as a single electrophoretic band in isoelectric focusing polyacrylamide gel electrophoresis (PAGE), with an isoelectric point of pH 4.4. The apparent molecular mass of the native enzyme was estimated by gel filtration to be 52 kDa. Sodium dodecyl sulfate (SDS)-PAGE under nonreducing conditions revealed the presence of a single polypeptide of 51 kDa. SDS-PAGE of CP3 reacted with 2-mercaptoethanol revealed the presence of two polypeptides of 31 and 18 kDa, indicating a dimer structure (alpha 1 beta 1) of the enzyme with disulfide-linked subunits. By using [1,3-3H]diisopropylfluorophosphate as an active-site labeling reagent, it was determined that the catalytic site resides on the small subunit of the carboxypeptidase. With N-carboben zoxy-L-phenylalanyl-L-leucine (N-CBZ-Phe-Leu) as the substrate, the Km, kcat, and Vmax values were 1.7 x 10(-4) M, 490 s-1, and 588 mumol of Leu released per min per mg of protein, respectively. CP3 was determined to be a serine protease, since its catalytic activity was blocked by the serine protease inhibitors diisopropylfluorophosphate, phenylmethylsulfonyl fluoride, and 3,4-dichloroi Socoumarin (DCI). The enzyme was strongly inhibited by the mercurial compound p-chloromercuribenzoate. The carboxypeptidase readily hydrolyzed peptides with aliphatic or aromatic side chains, whereas most of the peptides which contained glycine in the penultimate position did not serve as substrates for the enzyme. Although CP3 activity was undetectable in Mucor yeast cells, antisera revealed the presence of the enzyme in the yeast form of the fungus. The partial amino acid sequence of the carboxypeptidase was determined.
PMCID: PMC205736  PMID: 1729237

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