The posttranslational methylation of N-terminal α-amino groups (α-N-methylation) is a ubiquitous reaction found in all domains of life. Although this modification usually occurs on protein substrates, recent studies have shown that it also takes place on ribosomally synthesized natural products. Here we report an investigation of the bacterial α-N-methyltransferase CypM involved in the biosynthesis of the peptide antibiotic cypemycin. We demonstrate that CypM has low substrate selectivity and methylates a variety of oligopeptides, cyclic peptides such as nisin and haloduracin, and the ε-amino group of lysine. Hence it may have potential for enzyme engineering and combinatorial biosynthesis. Bayesian phylogenetic inference of bacterial α-N-methyltransferases suggests that they have not evolved as a specific group based on the chemical transformations they catalyze, but that they have been acquired from various other methyltransferase classes during evolution.

MicroRNA (miRNA) are a class of non-coding RNA that suppress gene expression by degradation or translational inhibition of target RNA. Several miRNA have been shown to target oncogenes and recently miRNA-125b was shown to translationally and transcriptionally inhibit the p53 gene. Here, we show that an additional isomer of miRNA-125 (miRNA-125a) translationally arrests mRNA of the p53 tumor suppressor gene. The basis of this activity is the high degree of sequence homology between the seed sequence of miR-125a and the 3′-UTR of p53. Our findings add miRNA-125a to the growing list of miRNA with oncogenic targets.

The ubihydroquinone: cytochrome c oxidoreductase, or cytochrome bc1, is a central component of photosynthetic and respiratory energy transduction pathways in many organisms. It contributes to the generation of membrane potential and proton gradient used for cellular energy production (ATP). The three-dimensional structures of cytochrome bc1 indicate that its two monomers are intertwined to form a symmetrical homodimer. This unusual architecture raises the issue of whether the monomers operate independently, or function cooperatively during the catalytic cycle of the enzyme. In this review, recent progress achieved in our understanding of the mechanism of function of dimeric cytochrome bc1 is presented. New genetic approaches producing heterodimeric enzymes, and emerging insights related to the inter monomer electron transfer between the heme b cofactors of cytochrome bc1 are described.

Redox reactions of tyrosine play key roles in many biological processes, including water oxidation and DNA synthesis. We first review the redox properties of tyrosine (and other phenols) in small molecules and related polypeptides, then report work on (H20)/(Y48)-modified Pseudomonas aeruginosa azurin. The crystal structure of this protein (1.18 Å resolution) shows that H20 is strongly hydrogen bonded to Y48 (2.7–2.8 Å tyrosine-O to histidine-N distance). A firm conclusion is that proper tuning of the tyrosine potential by a proton-accepting base is critical for biological redox functions.

Pluripotent stem cells hold enomous potential for therapuetic applications in tissue replacement therapy. Reprogramming somatic cells from a patient donor to generate pluripotent stem cells involves both ethical concerns inherent in the use of embryonic and oocyte-derived stem cells, as well as issues of histocompatibility. Among the various pluripotent stem cells, induced pluripotent stem cells (iPSC)—derived by ectopic expression of four reprogramming factors in donor somatic cells—are superior in terms of ethical use, histocompatibility, and derivation method. However, iPSC also show genetic and epigenetic differences that limit their differentiation potential, functionality, safety, and potential clinical utility. Here, we discuss the unique characteristics of iPSC and approaches that are being taken to overcome these limitations.

Endothelial inflammation plays a critical role in the development and progression of cardiovascular disease, albeit the mechanisms need to be fully elucidated. We here report that treatment of human umbilical vein endothelial cells (HUVECs) with tumor necrosis factor (TNF) α substantially increased the expression of MCP-induced protein 1 (MCPIP1). Overexpression of MCPIP1 protected ECs against TNFα-induced endothelial activation, as characterized by the attenuation in the expression of the adhesion molecule VCAM-1 and monocyte adherence to ECs. Conversely, small interfering RNA-mediated knock down of MCPIP1 increased the expression of VCAM-1 and monocytic adherence to ECs. These studies identified MCPIP1 as a feedback control of cytokines-induced endothelial inflammation.

Highlights

► α2M is an extracellular chaperone able to inhibit protein aggregation. ► Protease–α2M complexes can degrade amyloidogenic substrates or act as a chaperone. ► Activated α2M may play an important role in preventing protein deposition in vivo.

α2-Macroglobulin (α2M) is an extracellular chaperone that inhibits amorphous and fibrillar protein aggregation. The reaction of α2M with proteases results in an ‘activated’ conformation, where the proteases become covalently-linked within the interior of a cage-like structure formed by α2M. This study investigates, the effect of activation on the ability of α2M to inhibit amyloid formation by Aβ1–42 and I59T human lysozyme and shows that protease-activated α2M can act via two distinct mechanisms: (i) by trapping proteases that remain able to degrade polypeptide chains and (ii) by a chaperone action that prevents misfolded clients from continuing along the amyloid forming pathway.

Structured summary of protein interactions

Aβ1–42 and Aβ1–42 bind by fluorescence technology (View interaction)I59T lysozyme and I59T lysozyme bind by light scattering (View interaction)I59T lysozyme and I59T lysozyme bind by fluorescence technology (View interaction)Alpha-lactalbumin and Alpha-lactalbumin bind by fluorescence technology (View interaction)I59T lysozyme and I59T lysozyme bind by electron microscopy (View interaction)Aβ1–42 and Aβ1–42 bind by electron microscopy (View interaction)

Aquaporin-1 (AQP1) inhibitors are predicted to have multiple clinical applications. Hg++ is a non-specific and toxic AQP1 blocker. We compared compounds with reported AQP1 inhibition activity, including DMSO, Au+++, Ag+, tetraethylam-monium and acetazolamide. Water permeability was measured by stopped-flow light scattering in erythrocytes and volume marker dilution in epithelial cells. Au+++ inhibited AQP1 with IC50 ∼ 14 μM, similar to 10 μM for Hg++. DMSO slowed osmotic equilibration; however, the apparent inhibition was due to ‘osmotic clamp’ rather than AQP1 inhibition. Neither tetraethylammonium nor acetazolamide (to 10 mM) inhibited AQP1. Our data indicate the need to identify new AQP1 inhibitors. Published by Elsevier B.V. on behalf of the Federation of European Biochemical Societies.

Wiskott-Aldrich Syndrome (WAS) is a X-linked primary immunodeficiency disorder also marked by a very high (up to 70%) incidence of autoimmunity. Wiskott-Aldrich Syndrome arises from mutations in the Wiskott-Aldrich Syndrome protein (WASp), a cytoplasmic protein that links signaling by cell surface receptors such as the T-cell receptor and integrins to actin polymerization. WASp promotes the functions of multiple cell types that support immune responses, but also is important for the function of regulatory T cells and in TCR-induced apoptosis, two negative mechanisms of immune regulation that maintain peripheral immune tolerance. Here we review the nature of immune defects and autoimmunity in WAS and WASp deficient mice and discuss how this single gene defect can simultaneously impair immune responses to pathogens and promote autoimmunity. The myriad cellular immune defects found in WAS make this Mendelian syndrome an interesting model for the study of more complex immune diseases that arise from the interplay of environmental and multiple genetic risk factors.

Insulin-, and contraction-induced GLUT4 and fatty acid (FA) transporter translocation may share common trafficking mechanisms. Our objective was to examine the effects of partial Munc18c ablation on muscle glucose and FA transport, FA oxidation, GLUT4 and FA transporter (FAT/CD36, FABPpm, FATP1, FATP4) trafficking to the sarcolemma, and FAT/CD36 to mitochondria. In Munc18c−/+ mice, insulin-stimulated glucose transport and GLUT4 sarcolemmal appearance were impaired, but were unaffected by contraction. Insulin- and contraction-stimulated FA transport, sarcolemmal FA transporter appearance, and contraction-mediated mitochondrial FAT/CD36 were increased normally in Munc18c−/+ mice. Hence, Munc18c provides stimulus-specific regulation of GLUT4 trafficking, but not FA transporter trafficking.

To test the hypothesis that α-crystallin chaperone activity plays a central role in maintenance of lens transparency, we investigated its interactions with γ-crystallin mutants that cause congenital cataract in mouse models. Although the two substitutions, I4F and V76D, stabilize a partially unfolded γD-crystallin intermediate, their affinities to α-crystallin are marginal even at relatively high concentrations. Detectable binding required further reduction of γD-crystallin stability which was achieved by combining the two mutations. Our results demonstrate that mutants and possibly age-damaged γ-crystallin can escape quality control by lens chaperones rationalizing the observation that they nucleate protein aggregation and lead to cataract.

Hypoxic preconditioning (HP) is an evolutionarily-conserved mechanism that protects an organism against stress. The mitochondrial ATP-sensitive K+ channel (mKATP) plays an essential role in the protective signaling, but remains molecularly undefined. Several lines of evidence suggest that mKATP may arise from an inward rectifying K+ channel (Kir). The genetic model organism C. elegans exhibits HP and displays mKATP activity. Here, we investigate the tissue expression profile of the three C. elegans Kir genes and demonstrate that mutant strains where the irk genes have been deleted either individually or in combination can be protected by HP and exhibit robust mKATP channel activity in purified mitochondria. These data suggest that the mKATP in C. elegans does not arise from a Kir derived channel.

B.pertussis adenylate cyclase toxin (ACT) intoxicates cells by producing intracellular cAMP. B.pertussis outer membrane vesicles (OMV) contain ACT on their surface (OMV-ACT), but the properties of OMV-ACT were previously unknown. We found that B.pertussis in the lung from a fatal pertussis case contains OMV, suggesting an involvement in pathogenesis. OMV-ACT and ACT intoxicate cells with and without the toxin’s receptor CD11b/CD18. Intoxication by ACT is blocked by antitoxin and anti-CD11b antibodies, but not by cytochalasin-D; in contrast, OMV-ACT is unaffected by either antibody and blocked by cytochalasin-D. Thus OMV-ACT can deliver ACT by processes distinct from those of ACT alone.

When mast cells contact a monovalent antigen-bearing fluid lipid bilayer, IgE-loaded FcεRI receptors aggregate at contact points and trigger degranulation and the release of immune activators. We used two-color total internal reflection fluorescence microscopy and single-particle tracking to show that most fluorescently labeled receptor complexes diffuse freely within these micron-size clusters, with a diffusion coefficient comparable to free receptors in resting cells. At later times, when the small clusters coalesce to form larger patches, receptors diffuse even more rapidly. In all cases, Monte Carlo diffusion simulations ensured that the tracking results were free of bias, and distinguished biological from statistical variation. These results show the diversity in receptor mobility in mast cells, demonstrating at least three distinct states of receptor diffusivity.

Peroxidation of cardiolipin in mitochondria is essential for the execution of apoptosis. We suggested that integration of oleic acid into cardiolipin generates non-oxidizable cardiolipin species hence protects cells against apoptosis. We synthesized mitochondria-targeted triphenylphosphonium oleic acid ester. Using lipidomics analysis we found that pretreatment of mouse embryonic cells with triphenylphosphonium oleic acid ester resulted in decreased contents of polyunsaturated cardiolipins and elevation of its species containing oleic acid residues. This caused suppression of apoptosis induced by actinomycin D. Triacsin C, an inhibitor of acyl-CoA synthase, blocked integration of oleic acid into cardiolipin and restored cell sensitivity to apoptosis.

The C-terminal regions (CT) of Pfam PF04740 proteins share significant sequence identity with the toxic CdiA-CT effector domains of contact-dependent growth inhibition (CDI) systems. In accord with this homology, we find that several PF04740 CT domains inhibit cell growth when expressed in E. coli. This growth inhibition is specifically blocked by antitoxin proteins encoded downstream of each PF04740 gene. The YobL-CT, YxiD-CT and YqcG-CT domains from B. subtilis 168 have cytotoxic RNase activities, which are neutralized by the binding of cognate YobK, YxxD and YqcF antitoxin proteins, respectively. Our results show that PF04740 proteins represent a new family of toxin/antitoxin pairs that are widely distributed in Gram-positive bacteria.

The FMN–heme intraprotein electron transfer (IET) kinetics in full length and oxygenase/FMN (oxyFMN) construct of human iNOS were determined by laser flash photolysis over the temperature range from 283 to 304 K. An appreciable increase in the rate constant value was observed with an increase in the temperature. Our previous viscosity study indicated that the IET process is conformationally gated, and Eyring equation was thus used to analyze the temperature dependence data. The obtained magnitude of activation entropy for the IET in the oxyFMN construct is only one-fifth of that for the holoenzyme. This indicates that the FMN domain in the holoenzyme needs to sample more conformations before the IET takes place, and that the FMN domain in the oxyFMN construct is better poised for efficient IET.

Botulinum neurotoxins (BoNTs) cause botulism by cleaving proteins necessary for nerve transmission. There are seven serotypes of BoNT, A-G, characterized by their response to antisera. Many serotypes are further distinguished into differing subtypes based on amino acid sequence some of which result in functional differences. Our laboratory previously reported that all tested subtypes within each serotype have the same site of enzymatic activity. Recently, three new subtypes of BoNT/F; /F3, /F4, and /F5, were reported. Here, we report that BoNT/F5 cleaves substrate synaptobrevin-2 in a different location than the other BoNT/F subtypes, between 54L and 55E. This is the first report of cleavage of synaptobrevin-2 in this location.

Transforming growth factor beta (TGFβ) is a multipotent cytokine that is sequestered in the extracellular matrix (ECM) through interactions with a number of ECM proteins. The ECM serves to concentrate latent TGFβ at sites of intended function, to influence the bioavailability and/or function of TGFβ activators, and perhaps to regulate the intrinsic performance of cell surface effectors of TGFβ signal propagation. The downstream consequences of TGFβ signaling cascades in turn provide feedback modulation of the ECM. This review covers recent examples of how genetic mutations in constituents of the ECM or TGFβ signaling cascade result in altered ECM homeostasis, cellular performance and ultimately disease, with an emphasis on emerging therapeutic strategies that seek to capitalize on this refined mechanistic understanding.

Gap junctional intercellular communication (GJIC) regulates cellular homeostasis by propagating signaling molecules, exchanging cellular metabolites, and coupling electrical signals. In cancer, cells exhibit altered rates of GJIC which may play a role in neoplastic progression. KATP channels help maintain membrane polarity; and, linkages between KATP channel activity and rates of GJIC have been established. The mechanistic relationship has not been fully elucidated. We report the effects of treatment with multiple KATP antagonist compounds on GJIC in metastatic cell lines demonstrating an increase in communication rates following treatment with compounds possessing specificities towards the SUR2 subunit of KATP. These effects remained consistent using cell lines with different expression levels of SUR1 and SUR2, suggesting possible off target effects on GJIC by these compounds.

FadA, a novel adhesin of periodontal pathogen Fusobacterium nucleatum is composed of two forms, pre-FadA and mature FadA (mFadA), constituting the functional FadA complex (FadAc). By electron microscopy, we observed that mFadA formed uniformly long and thin filaments, while FadAc formed heterogeneous filaments of varying lengths and widths, as well as “knots”. Mutants in signal peptide or in the non-alpha helical loop retaining heterogeneous structures had binding activity while those forming aggregates or long filaments lost activity. These observations suggest short filaments and knots may be the active forms of FadA. This is the first demonstration that a signal peptide is required for the assembly of a bacterial adhesin.

Murine L1Md-A5 retrotransposon is a redox-inducible element regulated by Nrf-2/JunD and E2F/Rb-binding sites within its promoter (5′-UTR). Because the human papillomavirus (HPV) oncoprotein E7 interacts with retinoblastoma (pRb) and members of the AP1 family, studies were conducted to examine functional interactions between HPV E7, pRb, and histone deacetylase 2 (HDAC2) in the regulation of L1Md-A5. Using a transient heterologous transcription system we found that HPV E7 alone, or in combination with HDAC2, disrupted pRb-mediated L1MdA-5 transactivation. HPV E7 also ablated the transcriptional response of L1Md-A5 to genotoxic stress, but did not interfere with basal activity. We conclude that HPV E7 associates with proteins involved in the assembly of macromolecular complexes that regulate antioxidant and E2F/Rb sites within L1MdA-5 to regulate biological activity

Streptomyces erythraeus trypsin (SET) is a serine protease that is secreted extracellularly by Streptomyces erythraeus. We investigated the inhibitory effect of α1-antitrypsin on the catalytic activity of SET. Intriguingly, we found that SET is not inhibited by α1-antitrypsin. Our investigations into the molecular mechanism underlying this observation revealed that SET hydrolyzes the Met-Ser bond in the reaction center loop of α1-antitrypsin. However, SET somehow avoids entrapment by α1-antitrypsin. We also confirmed that α1-antitrypsin loses its inhibitory activity after incubation with SET. Thus, our study demonstrates that SET is not only resistant to α1-antitrypsin but also inactivates α1-antitrypsin.

We show that diacylglycerol kinase-ε (DGKε) has less preference for the acyl chain at the sn-1 position of diacylglycerol (DAG) than the one at the sn-2 position. Although DGKε discriminates between 1-stearoyl-2-arachidonoyl-DAG and 1-palmitoyl-2-arachidonoyl-DAG, it has similar substrate preference for 1-stearoyl-2-arachidonoyl-DAG and 1,2-diarachidonoyl-DAG. We suggest that in addition to binding to the enzyme, the acyl chain at the sn-1 position may contribute to the depth of insertion of the DAG into the membrane. Thus, the DAG intermediate of the PI-cycle, 1-stearoyl-2-arachidonoyl-DAG, is not the only DAG that is a good substrate for DGKε, the DGK isoform involved in PI-cycling.

The shared epitope (SE) - an HLA-DRB1-encoded 5-amino acid sequence motif carried by the vast majority of rheumatoid arthritis (RA) patients - is a risk factor for severe disease. The mechanistic basis of RA-SE association is unknown. This group has previously demonstrated that the SE acts as a signal transduction ligand that activates nitric oxide and reactive oxygen species production. SE-activated signaling depends on cell surface calreticulin, a known innate immunity receptor previously implicated in immune regulation, autoimmunity and angiogenesis. Recent evidence that the SE enhances the polarization of Th17 cells, which is a key mechanism in autoimmunity, is discussed highlighting one of several potential functional effects of the SE in RA.