Enzyme promoted assembly offers a simple and straightforward means to construct monodisperse molecular objects too large for classical organic synthesis and too small for top-down techniques. This communication outlines the design and construction of a heterobifunctional protein building block, HaloTag-cutinase, that reacts rapidly and selectively with an appropriately functionalized small molecule linker; and describes the step-wise combination of these building blocks to generate a 300 kDa “megamolecule” that is precisely-defined with respect to domain orientation, connectivity, and composition.
megamolecules; protein-based materials; nanostructured materials; modular synthesis; bioconjugation
biosynthesis; validamycin; enzyme catalysis; dioxygenase; VldW
influenza; antibodies; neuraminidase inhibitor; click chemistry; conjugation
Sigma (σ) receptors represent unique non-opioid binding sites that are associated with a broad range of disease states. Sigma-2 receptors provide a promising target for diagnostic imaging and pharmacological interventions to curb tumor progression. Most recently, the progesterone receptor (PGRMC1, 25 kDa) has been identified to contain σ2 receptor-like binding properties, highlighting the need to understand the biological function of an 18-kDa protein that exhibits σ2-like photoaffinity labeling (herein denoted as σ2-18k) but the amino acid sequence of which is not known. In order to provide novel tools for the study of the σ2-18k protein, we have developed bifunctional sigma receptor ligands that bear a benzophenone photo-crosslinking moiety and an alkyne group, to which an azide-containing biotin affinity tag can be covalently attached via click chemistry following photo-crosslink. While several compounds showed favorable σ2 binding properties, compound 22 exhibited the highest affinity (2 nM) and the greatest potency in blocking photolabeling of the σ2-18k by a radioactive photoaffinity ligand. Thus, these benzophenone-alkyne sigma receptor ligands may be amenable for studying the σ2-18k protein via chemical biology approaches. To our knowledge, these compounds represent the first reported benzophenone-containing clickable sigma receptor ligands, which may potentially serve broad applications by “plugging” in various tags.
Sigma-2 receptor ligand; σ2-18k; benzophenone; alkyne; click chemistry
Small changes – big effect A new aureothin derivative, aureopyran, that features an unusual pyran backbone was generated by simply altering the enzymatic methylation topology. The α-pyrone ring hampers the correct placement of the polyketide backbone in the multifunctional cytochrome P450 monooxygenase AurH. Instead of a THF ring an oxo intermediate is formed that readily undergoes a rare electrocyclization reaction.
Aureothin; AurH; Combinatorial biosynthesis; Cytochrome P450 monooxygenase; Polyketide
Impediments to DNA access due to assembly of the eukaryotic genome into chromatin are in part overcome by the activity of ATP-dependent chromatin-remodeling complexes. These complexes employ energy derived from ATP hydrolysis to destabilize histone—DNA interactions and alter nucleosome positions, thereby increasing the accessibility of DNA-binding factors to their targets. However, the mechanism by which theses complexes accomplish this task remains unresolved. We review aspects of nucleosome alteration by the SWI/SNF complex, the archetypal remodeling enzyme. We focus on experiments that provide insights into how SWI/SNF induces nucleosome movement along DNA. Numerous biochemical activities have been characterized for this complex, all likely providing clues as to the molecular mechanism of translocation.
chromatin; DNA structure; gene expression; remodeling enzymes; SWI/SNF
enzymes; fluorine; inhibitors; nucleotides
The synthesis and in vitro evaluation of new Pup-based fluorogenic substrates for Dop, the mycobacterial depupylase, are described. A full length Pupamidomethylcoumarin conjugate as well as an amino-terminal truncated analog exhibited high sensitivity and specificity towards hydrolysis by Dop. As Dop is required for the full virulence of Mycobacterium tuberculosis, it is an attractive new drug target and the fluorogenic substrates developed here may find application as high-throughput screening assay reagents for the identification of Dop inhibitors.
Tuberculosis; Deamidase of Pup (Dop); Pup-proteasome system (PPS); Fluorescent probes; Protein-protein interactions
The rates of oxidation of fatty acids by CYP119 Compound I were dependent on the pH of the medium. The plot shows log k for reactions of acids as a function of pH, where the slopes indicate mixed third-order and fourth-order dependence on base concentration. For palmitic acid, the rate increased by a factor of 50 over the pH range of 6.8 to 7.3.
cytochrome P450; oxidation; fatty acids; kinetics; regioselectivity
In an attempt to identify novel small molecule ligands of CDK2 with potential as allosteric inhibitors, we devised a robust and cost-effective fluorescence-based high-throughput screening assay. The assay is based on the specific interaction of CDK2 with the extrinsic fluorophore 8-anilino-1-naphthalene sulfonate (ANS), which binds to a large allosteric pocket adjacent to the ATP site. Hit compounds which displace ANS directly or indirectly from CDK2 are readily classified as ATP site binders or allosteric ligands through the use of staurosporine, which blocks the ATP site without displacing ANS. Pilot screening of 1,453 compounds led to the discovery of 12 compounds with displacement activities (EC50 values) ranging from 6 to 44 μM, all of which were classified as ATP site-directed ligands. Four new Type I inhibitor scaffolds were confirmed by X-ray crystallography. While this small compound library contained only ATP-site directed ligands, the application of this assay to large compound libraries has the potential to reveal previously unrecognized chemical scaffolds suitable for structure-based design of CDK2 inhibitors with new mechanisms of action.
high-throughput screening; drug discovery; chemical probes; allosteric inhibitors; protein-protein interaction inhibitors
Histone acetyltransferase enzymes (HATs) are important therapeutic targets, but there are few cell-based assays available for evaluating the pharmacodynamics of HAT inhibitors. Here we present the application of a FRET-based reporter, Histac, in live cell studies of p300/CBP HAT inhibition, by both genetic and pharmacologic disruption. shRNA knockdown of p300/CBP led to increased Histac FRET, suggesting a role for p300/CBP in the acetylation of the histone H4 tail present. Additionally, we describe a new p300/CBP HAT inhibitor, C107, and show that it can also increase cellular Histac FRET. Taken together, these studies provide a live cell strategy for identifying and evaluating p300/CBP inhibitors.
drug design; enzymes; FRET; protein modifications; Histone H4
The serine hydrolases constitute a large class of enzymes that play important roles in physiology. There is great interest in the development of potent and selective pharmacological inhibitors to these proteins. Traditional active site inhibitors often have limited selectivity within this superfamily and are tedious and expensive to discover. Using the serine hydrolase RBBP9 as a model target, we report here a rapid and relatively inexpensive route to highly selective peptoid-based inhibitors that can be activated with visible light. This technology provides rapid access to photo-activated tool compounds capable of selectively blocking the function of particular serine hydrolases.
peptoid library; one-bead-one-compound; serine hydrolase; ABPP; CALI; RBBP9
biological activity; cage compounds; chemical biology; light regulation; photochemistry
A light-activatable bacteriophage T7 RNA polymerase (T7RNAP) has been generated through the site-specific introduction of a photocaged tyrosine residue at the crucial position Tyr639 within the active site of the enzyme. The photocaged tyrosine disrupts polymerase activity by blocking the incoming nucleotide from reaching the active site of the enzyme. However, a brief irradiation with nonphototoxic UV light of 365 nm removes the ortho-nitrobenzyl caging group from Tyr639 and restores the RNA polymerase activity of T7RNAP. The complete orthogonality of T7RNAP to all endogenous RNA polymerases in pro- and eukaryotic systems allowed for the photochemical activation of gene expression in bacterial and mammalian cells. Specifically, E. coli cells were engineered to produce photocaged T7RNAP in the presence of a GFP reporter gene under the control of a T7 promoter. UV irradiation of these cells led to the spatiotemporal activation of GFP expression. In an analogous fashion, caged T7RNAP was transfected into human embryonic kidney (HEK293T) cells. Irradiation with UV light led to the activation of T7RNAP, thereby inducing RNA polymerization and expression of a luciferase reporter gene in tissue culture. The ability to achieve spatiotemporal regulation of orthogonal RNA synthesis enables the precise dissection and manipulation of a wide range of cellular events, including gene function.
amino acids; caged proteins; light activation; polymerases; RNA
fatty acids; fungal metabolites; phosphopantetheinylation; polyketides; protein-protein interaction
Immunoproteasome; Activity-based probe; NIR-fluorescent probe
histones; chromatin; histone methylation; transcription; replication
cytokines; C-glycosides; glycosphingolipid; immunostimulant; Nozaki-Hiyama-Kishi reaction
We show that mushroom tyrosinase catalyzes formation of reactive o-quinones on unstructured, tyrosine-rich sequences such as hemagglutinin (HA)-tags (YPYDVPDYA). In the absence of exogenous nucleophiles and at low protein concentrations, the o-quinone decomposes with fragmentation of the HA-tag. At higher protein concentrations (>5 mg/ml), cross-linking is observed. Besthorn’s reagent intercepts the o-quinone to give a characteristic pink complex, which can be observed directly on a denaturing SDS-PAGE gel. Similar labeled species can be formed using other nucleophiles such as Cy5-hydrazide. These reactions are selective for proteins bearing HA- and other unstructured poly-tyrosine-containing tags and can be performed in lysates to create specifically tagged proteins.
labeling; o-quinone; cross-link; mechanism; protein derivatization)
Synthetic diacylglycerol lactones (DAG-lactones) are effective modulators of critical cellular signaling pathways, downstream of the lipophilic second messenger diacylglycerol, that activate a host of protein kinase C (PKC) isozymes and other non-kinase proteins that share with PKC similar C1 membrane-targeting domains. A fundamental determinant of the biological activity of these amphiphilic molecules is the nature of their interactions with cellular membranes. This study examines the biological properties of charged DAG-lactones exhibiting different alkyl groups attached to the heterocyclic nitrogen of an α–pyridylalkylidene chain, and particularly the relationship between membrane interactions of the substituted DAG-lactones and their respective biological activities. Our results suggest that bilayer interface localization of the N-alkyl chain in the R2 position of the DAG-lactones inhibits translocation of PKC isoenzymes onto the cellular membrane. However, the orientation of a branched alkyl chain at the bilayer surface facilitates PKC binding and translocation. This investigation emphasizes that bilayer localization of the aromatic side residues of positively-charged DAG lactone derivatives play a central role in determining biological activity and that this factor contributes to the diversity of biological actions of these synthetic biomimetic ligands.
diacylglycerol (DAG)-lactones; PKC; plasma membrane; membrane anchoring; vesicles
Protein–protein interactions (PPIs) are central to biological processes and represent an important class of therapeutic targets. Here we show that the interaction between FK506 binding protein 12 fused to green fluorescent protein (GFP-FKBP) and the rapamycin-binding domain of mTor fused to Escherichia coli dihydrofolate reductase (FRB-eDHFR) can be sensitively detected (signal-to-background (S:B) >100) and accurately quantified within an impure cell lysate matrix using a luminescence resonance energy transfer (LRET) assay. Ascomycin-mediated inhibition of GFP-FKBP/rapamycin/FRB-eDHFR complex formation was also detected at high S:B (>80) and Z’-factor (0.89). The method leverages the selective, stable binding of trimethoprim (TMP)-terbium complex conjugates to eDHFR, and time-resolved, background-free detection of the long-lifetime (~ms) terbium-to-GFP LRET signal that indicates target binding. TMP/eDHFR labeling can be adapted to develop high-throughput screening assays and complementary, quantitative counter-screens for a wide variety of PPI targets with a broad range of affinities that may not be amenable to purification.
FRET; high-throughput screening; Lanthanoids; Luminescence; Protein-Protein Interactions
fluorescent probes; live-cell imaging; genetically encoded proteins; malachite green; tetramethylrhodamine
Aminoimidazole carboxamide ribonucleotide transformylase/inosine monophosphate cyclohydrolase (ATIC) is a bifunctional homodimeric enzyme that catalyses the last two steps of de novo purine biosynthesis. Homodimerization of ATIC, a protein-protein interaction with an interface of over 5000 Å2, is required for its aminoimidazole carboxamide ribonucleotide (AICAR) transformylase activity, with the active sites forming at the interface of the interacting proteins. Here, we report the development of a small-molecule inhibitor of AICAR transformylase that functions by preventing the homodimerization of ATIC. The compound is derived from a previously reported cyclic hexa-peptide inhibitor of AICAR transformylase (with a Ki of 17 μM), identified by high-throughput screening. The active motif of the cyclic peptide is identified as an arginine-tyrosine dipeptide, a capped analogue of which inhibits AICAR transformylase with a Ki of 84 μM. A library of non-natural analogues of this dipeptide was designed, synthesized, and assayed. The most potent compound inhibits AICAR transformylase with a Ki of 685 nM, a 25-fold improvement in activity from the parent cyclic peptide. The potential for this AICAR transformylase inhibitor in cancer therapy is assessed by studying its effect on the proliferation of a model breast cancer cell line. Using a non-radioactive proliferation assay and live cell imaging, a dose-dependent reduction in cell numbers and cell division rates was observed in cells treated with our ATIC dimerization inhibitor.
AICAR Transformylase; ATIC; Protein-protein interaction Inhibitor; peptide; cancer
The regulation of antibody reporting intensities is critical to various in situ fluorescence imaging analyses. While such control is often necessary to visualize sparse molecular targets, the ability to tune marker intensities is also essential for highly multiplexed imaging strategies where marker reporting levels must be tuned to both optimize dynamic detection ranges and minimize crosstalk between different signals. Existing chemical amplification approaches generally lack such control. Here, we demonstrate that linear and branched DNA complexes can be designed to function as interchangeable building blocks that can be assembled into organized, fluorescence reporting complexes. We show that the ability to program DNA strand displacement reactions between these complexes offer new opportunities to deterministically tune the number of dyes that are coupled to individual antibodies in order to both increase and controllably balance marker levels within fixed cells.
antibodies; immunofluorescence; DNA strand displacement; dynamic DNA; multiplexed detection