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At least 487 records · Page 27Linked to original sources

bioRxiv2017

The molecular basis for Pompe disease revealed by the structure of human acid α-glucosidase

Pompe disease results from a defect in human acid -glucosidase (GAA), a lysosomal enzyme that cleaves terminal 1-4 and 1-6 glucose from glycogen. In Pompe disease (also known as Glycogen Storage Disorder type II), the accumulation of undegraded glycogen in lysosomes leads to cellular dysfunction, primarily in muscle and heart tissues. Pompe disease is an active candidate of clinical research, with pharmacological chaperone therapy tested and enzyme replacement therapy approved. Despite production of large amounts of recombinant GAA annually, the structure of GAA has not been reported until now. Here, we describe the first structure of GAA, at 1.7[A] resolution. Three structures of GAA complexes reveal the molecular basis for the hundreds of mutations that lead to Pompe disease and for pharmacological chaperoning in the protein. The GAA structure reveals a surprising second sugar-binding site 34[A] from the active site, suggesting a possible mechanism for processing of large glycogen substrates. Overall, the structure will assist in the design of next-generation treatments for Pompe disease.

biochemistry↗

bioRxiv2017

Inferring amino acid interactions underlying protein function

Protein function arises from a poorly defined pattern of cooperative energetic interactions between amino acid residues. Strategies for deducing this pattern have been proposed, but lack of benchmark data has limited experimental verification. Here, we extend deep-mutation technologies to enable measurement of many thousands of pairwise amino acid couplings in members of a protein family. The data show that despite great evolutionary divergence, homologous proteins conserve a sparse, spatially distributed network of cooperative interactions between amino acids that underlies function. This pattern is quantitatively captured in the coevolution of amino acid positions, especially as indicated by the statistical coupling analysis (SCA), providing experimental confirmation of the key tenets of this method. This work establishes a clear link between physical constraints on protein function and sequence analysis, enabling a general practical approach for understanding the structural basis for protein function.

biochemistry↗

bioRxiv2017

A hyperthermophilic phage decoration protein suggests common evolutionary origin with Herpesvirus Triplex proteins and an anti-CRISPR protein

Virus capsid proteins reproducibly self-assemble into regularly-shaped, stable shells that protect the viral genome from external environmental assaults, while maintaining the high internal pressure of the tightly packaged viral genome. To elucidate how capsids maintain stability under harsh conditions, we investigated the capsid components of a hyperthermophilic virus, phage P74-26. We determined the structure of a capsid protein gp87 and show that it has the same fold as trimeric decoration proteins that enhance the structural stability of capsids in many other phage, despite lacking significant sequence homology. We also find that gp87 is significantly more stable than its mesophilic homologs, reflecting the high temperature environment in which phage P74-26 thrives. Our analysis of the gp87 structure reveals that the core domain of the decoration protein is conserved in trimeric capsid components across numerous dsDNA viruses, including human pathogens such as Herpesviruses. Moreover, this core {beta}-barrel domain is found in the anti-CRISPR protein AcrIIC1, which suggests a mechanism for the evolution of this broad spectrum Cas9 inhibitor. Our work illustrates the principles for increased stability of a thermophilic decoration protein, and extends the evolutionary reach of the core trimeric decoration protein fold.

biochemistry↗

bioRxiv2017

Glutathione levels influence chronological life span of Saccharomyces cerevisiae in a glucose-dependent manner

Diet plays a key role in determining the longevity of the organisms since it has been demonstrated that glucose restriction increases lifespan whereas a high-glucose diet decreases it. However, the molecular basis of how diet leads to the aging process is currently unknown. We propose that the quantity of glucose that fuels respiration influences ROS generation and glutathione levels, and both chemical species impact in the aging process. Herein, we provide evidence that mutation of the gene GSH1 diminishes glutathione levels. Moreover, glutathione levels were higher with 0.5% than in 10% glucose in the gsh1{Delta} and WT strains. Interestingly, the chronological life span (CLS) was lowered in the gsh1{Delta} strain cultured with 10% glucose but not under dietary restriction. The gsh1{Delta} strain also showed an inhibition of the mitochondrial respiration in 0.5 and 10% of glucose but only increased the H2O2 levels under dietary restriction. These results correlate well with the GSH/GSSG ratio, which showed a decrease in gsh1{Delta} strain cultured with 0.5% glucose. Altogether these data indicate that glutathione has a major role in the function of electron transport chain (ETC) and is essential to maintain life span of Saccharomyces cerevisiae in 10% glucose.

biochemistry↗

bioRxiv2017

The effect of macromolecular crowding on single-round transcription by E. coli RNA polymerase

Biological reactions in the cellular environment differ physicochemically from those performed in dilute buffer solutions due to, in part, slower diffusion of various components in the cellular milieu, increase in their chemical activities, and modulation of their binding affinities and conformational stabilities. In vivo transcription is therefore expected to be strongly influenced by the crowdedness of the cell. Previous studies of transcription under macromolecular crowding conditions have focused mainly on multiple cycles of RNAP-Promoter associations, assuming that the association is the rate-determining step of the entire transcription process. However, recent reports demonstrated that late initiation and promoter escape could be the rate-determining steps for some promoter DNA sequences. The investigation of crowding effects on these steps under single-round conditions is therefore crucial for better understanding of transcription initiation in vivo. Here, we have implemented an in vitro transcription quenched-kinetics single-molecule assay to investigate the dependence of transcription reaction rates on the sizes and concentrations of crowders. Our results demonstrate an expected slowdown of transcription kinetics due to increased viscosity, and an unexpected enhancement in transcription kinetics by large crowding agents (at a given viscosity). More importantly, the enhancements dependence on crowder size significantly deviates from hard-sphere model (scaled-particle theory) predictions, commonly used for description of crowding effects. Our findings shed new light on how enzymatic reactions are affected by crowding conditions in the cellular milieu.

biochemistry↗

bioRxiv2017

Dimerization of the Pragmin pseudo-kinase regulates protein tyrosine phosphorylation

The pseudo-kinase and signaling protein Pragmin has been linked to cancer by regulating protein tyrosine phosphorylation via unknown mechanisms. Here we present the crystal structure of the Pragmin 906-1368 amino acids C-terminus, which encompasses its kinase domain. We show that Pragmin contains a classical protein kinase fold devoid of catalytic activity. A particular inhibitory triad, conserved in a Pragmin/SgK269/PEAK1/C19orf35 superfamily, tightly holds the catalytic lysine (K997) to prevent ATP binding. By proteomics, we discovered that this pseudo-kinase uses the tyrosine kinase CSK to induce protein tyrosine phosphorylation in human cells. Interestingly, the protein kinase domain is bordered by N- and C-terminal extensions forming an original dimerization domain that regulates Pragmin self-association and stimulates CSK activity. A1329E mutation in the C-terminal extension destabilizes Pragmin dimerization and reduces CSK activation. Thus, our results reveal a new dimerization mechanism by which a pseudo-kinase can induce protein tyrosine phosphorylation.

biochemistry↗

bioRxiv2017

Structure of transmembrane helix 8 and possible membrane defects in CFTR

The cystic fibrosis transmembrane conductance regulator (CFTR) is an ion channel that regulates the flow of anions across epithelia. Mutations in CFTR cause cystic fibrosis. CFTR belongs to the ATP-Binding Cassette (ABC) transporter superfamily, and gating is controlled by phosphorylation and ATP binding and hydrolysis. Recent ATP-free and ATP-bound structures of zebrafish CFTR revealed an unwound segment of transmembrane helix (TM) 8, which appears to be a unique feature of CFTR not present in other ABC transporter structures. Here, by means of 1 s long molecular dynamics simulations, we investigate the interactions formed by this TM8 segment with nearby helices, in both ATP-free and ATP-bound states. We highlight the structural role of TM8 in maintaining the functional architecture of the pore and we describe a distinct membrane defect that is found near TM8 only in the ATP-free state. The results of the MD simulations are discussed in the context of the gating mechanism of CFTR.

biochemistry↗

bioRxiv2017

Structure and function of accessory Sec proteins involved in the adhesin export pathway of Streptococcus gordonii

Many pathogenic bacteria, including Streptococcus gordonii, possess a pathway for the export of a single serine-rich-repeat protein that mediates the adhesion of bacteria to host cells and the extracellular matrix. These adhesins are O-glycosylated by several cytosolic glycosyltransferases and require three accessory Sec proteins (Asp1-3) for export, but how the adhesins are processed for secretion is not well defined. Here, we show that O-glycosylation of S. gordonii adhesin GspB occurs in a sequential manner by three enzymes (GtfA/B, Nss, Gly) that attach N-acetylglucosamine and glucose to Ser/Thr residues. The modified substrate is subsequently transferred from the last glycosyltransferase to the Asp1/2/3 complex. Crystal structures show that both Asp1 and Asp3 are related to carbohydrate binding proteins. Asp1 also has an affinity for phospholipids, which is attenuated by Asp2. These results suggest a mechanism for the modification of adhesin in the cytosol and its subsequent targeting to the export machinery.

biochemistry↗

bioRxiv2017

Atypical domain communication and domain functions of a Hsp110 chaperone

Hsp110s are well recognized nucleotide exchange factors (NEFs) of Hsp70s, in addition they are implicated in various aspects of cellular proteostasis as discrete chaperones with yet enigmatic molecular mechanism. Stark similarity in domain organization and structure between Hsp110s and Hsp70s, is easily discernible although the nature of domain communication and domain functions of Hsp110s are still puzzling. Here, we report atypical domain communication of yeast Hsp110, Sse1 using single molecule FRET, small angle X-ray scattering measurements (SAXS) and Molecular Dynamic simulations. Our data show that Sse1 lacks typical domain movements as exhibited by Hsp70s, albeit it undergoes unique structural alteration upon nucleotide and substrate binding. Hsp70-like domain-movements can be artificially salvaged in chimeric constructs of Hsp110-Hsp70 although such salvaging proves detrimental for the NEF activity of the protein. Furthermore, we show that substrate binding domain (SBD) of Hsp110, chaperones self, as well as foreign nucleotide binding domains (NBD). Interestingly, the substrate binding specificity of Hsp110 is largely determined by its NBD rather than SBD, the latter being the foremost substrate binding region for Hsp70s.

biochemistry↗

bioRxiv2017

Multi-Funnel Landscape of the Fold-Switching Protein RfaH-CTD

Proteins such as the transcription factor RfaH can change biological function by switching between distinct three-dimensional folds. RfaH regulates transcription if the C-terminal domain folds into a double helix bundle, and promotes translation when this domain assumes a {beta}-barrel form. This fold-switch has been also observed for the isolated domain, dubbed by us RfaH-CTD, and is studied here with a variant of the RET approach recently introduced by us. We use the enhanced sampling properties of this technique to map the free energy landscape of RfaH-CTD and to propose a mechanism for the conversion process.\n\n\n\nO_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=109 SRC=\"FIGDIR/small/221143_ufig1.gif\" ALT=\"Figure 1\">\nView larger version (23K):\norg.highwire.dtl.DTLVardef@17ce490org.highwire.dtl.DTLVardef@81ce9aorg.highwire.dtl.DTLVardef@230ddborg.highwire.dtl.DTLVardef@162be94_HPS_FORMAT_FIGEXP M_FIG TOC Image\n\nC_FIG

biochemistry↗

bioRxiv2017

Partitioning of semisynthetic lipidated N-Ras in lipid raft nanodomains determined by FRET to lipid domain markers

Cellular membranes are heterogeneous planar lipid bilayers displaying lateral phase separation with the nanometer-scale liquid-ordered phase (aka \"lipid rafts\" or Lo) surrounded by the liquid-disordered phase (Ld). Many membrane-associated proteins were found to stably integrate in the rafts, which is critical for their biological function. Isoforms H and N of Ras GTPase possess a unique ability to switch their lipid domain preference depending on the type of bound guanine nucleotide (GDP or GTP). This behavior, however, has never been reproduced in vitro in model bilayers with recombinant proteins, and therefore has been attributed to action of other proteins binding Ras at the membrane surface. In this paper, we report the observation of the nucleotide-dependent switch of lipid domain preferences of the semisynthetic lipidated N-Ras in raft lipid vesicles in the absence of other proteins. To detect segregation of Ras molecules in raft and disordered lipid domains, we measured Forster Resonance Energy Transfer (FRET) between the donor fluorophore, mant, attached to the protein-bound guanine nucleotides, and the acceptor, rhodamine-conjugated lipid, localized to the liquid-disordered domains. We demonstrated that N-Ras preferentially populated raft domains when bound to mant-GDP, while losing preference for rafts when it was associated with a GTP mimic, mant-GppNHp. At the same time, the isolated lipidated C-terminal peptide of N-Ras was found localized outside of the liquid-ordered rafts, most likely--in the bulk disordered lipid.

biochemistry↗

bioRxiv2017

Validating Antibodies for Quantitative Western Blot Measurements with Microwestern Array

Western blotting is often considered a semi-quantitative or even qualitative assay for assessing changes in protein or protein post-translational modification levels. Fluorescence-based measurement enables acquisition of quantitative data in principal, but requires determining the linear range of detection for each antibody--a labor-intensive task. Here, we describe the use of a high-throughput western blotting technique called microwestern array to more rapidly evaluate suitable conditions for quantitative western blotting with particular antibodies. We can evaluate up to 192 antibody/dilution/replicate combinations on a single standard size gel with a seven-point, two-fold lysate dilution series (~100-fold range). Pilot experiments demonstrate a surprisingly high proportion of investigated antibodies (17/22) are suitable for quantitative use, and that lack of validity might often be a consequence of lysate composition rather than antibody quality. Linear range for all validated antibodies is at least 8-fold, and in some cases nearly two orders of magnitude. That range could be greater as the presented tests did not find a limit for many antibodies. We find that phospho-specific and total antibodies do not have discernable trend differences in linear range or limit of detection, but total antibodies generally required higher working concentrations, suggesting phospho-specific antibodies may be generally higher affinity. Importantly, we demonstrate that results from microwestern analyses scale to normal \"macro\" western for a subset of antibodies. These data indicate that with initial validation, many antibodies can be readily used quantitatively in a reproducible manner. Antibody validation data and standard operating procedures are available online (www.birtwistlelab.com/protocols and www.dtoxs.org).

biochemistry↗

bioRxiv2017

Transgenic mouse lines expressing the 3xFLAG-dCas9 protein for enChIP analysis

We developed the engineered DNA-binding molecule-mediated chromatin immunoprecipitation (enChIP) technology to isolate specific genomic regions while retaining their molecular interactions. In enChIP, the locus of interest is tagged with an engineered DNA-binding molecule, such as a modified form of the clustered regularly interspaced short palindromic repeats (CRISPR) system containing a guide RNA (gRNA) and a catalytically inactive form of Cas9 (dCas9). The locus is then affinity-purified to enable identification of associated molecules. In this study, we generated transgenic mice expressing 3xFLAG-tagged Streptococcus pyogenes dCas9 (3xFLAG-dCas9) and retrovirally transduced gRNA into primary CD4+ T cells from these mice for enChIP. Using this approach, we achieved high yields of enChIP at the targeted genomic region. Our novel transgenic mouse lines provide a valuable tool for enChIP analysis in primary mouse cells.

biochemistry↗

bioRxiv2017

Structure of the nucleotide exchange factor eIF2B reveals mechanism of memory-enhancing molecule

Regulation by the integrated stress response (ISR) converges on the phosphorylation of translation initiation factor eIF2 in response to a variety of stresses. Phosphorylation converts eIF2 from substrate to competitive inhibitor of its dedicated guanine nucleotide exchange factor, eIF2B, inhibiting translation. ISRIB, a drug-like eIF2B activator, reverses the effects of eIF2 phosphorylation and, remarkably, in rodents enhances cognition and corrects cognitive deficits after brain injury. To determine its mechanism of action, we solved an atomic-resolution structure of ISRIB bound in a deep cleft within decameric human eIF2B by electron cryo-microscopy. Structural and biochemical analyses revealed that formation of fully active, decameric eIF2B holoenzyme depended on the assembly of two identical tetrameric subcomplexes, and that ISRIB promoted this step by cross-bridging a central symmetry interface. Regulation of eIF2B assembly emerges as a rheostat for eIF2B activity that tunes translation during the ISR and that can be further modulated by ISRIB.

biochemistry↗

bioRxiv2017

Attomol-level quantification of chemically modified ribonucleosides enabled by capillary porous graphitic carbon columns in nano LC-MS

Post-transcriptional chemical modifications of (t)RNA molecules are crucial in fundamental biological processes, such as translation. Despite their biological importance and accumulating evidence linking them to various human diseases, technical challenges have limited the development of methods for reliable detection and accurate quantification of these modifications. Here, we present a sensitive capillary nanoflow liquid chromatography mass spectrometry (nLC-MS) pipeline for quantitative high-resolution analysis of ribonucleoside modifications from complex biological samples. We evaluated two porous graphitic carbon (PGC) materials as stationary phases for reversed-phase separation of ribonucleosides and found that both PGC matrices have excellent retention and separation characteristics, as well as the capability to separate structural isomers. Using PGC matrices in nLC-MS yielded excellent signal-to-noise ratios in a detection range spanning up to six orders of magnitude, allowing for the analysis of individual ribonucleosides down to attomol concentrations. Furthermore, normalizing the obtained signal intensities to a stable isotope labeled spike-in enabled direct comparison of ribonucleoside levels between different samples. In conclusion, capillary PGC columns coupled to nLC-MS constitute a powerful and sensitive tool for quantitative analysis of chemically modified ribonucleosides in complex biological samples. This setup will be invaluable for further unraveling the intriguing and multifaceted biological roles of RNA modifications.

biochemistry↗

bioRxiv2017

Identification of key pathways and metabolic fingerprints of longevity in C. elegans

Impaired insulin/IGF-1 signaling (IIS) pathway and caloric restriction (CR) are two well-established interventions to prolong lifespan in worm C. elegans. However, a cross comparison of these longevity pathways using a multi-omics integration approach is lacking. In this study, we aimed to identify key pathways and metabolite fingerprints of longevity that are shared between IIS and CR worm models using a multi-omics integration approach. We generated transcriptomics and metabolomics data from two long-lived mutant worm strains, i.e. daf-2 (impaired IIS pathway) and eat-2 (CR model) and compared them with the N2 strain. Transcriptional profiling identified shared longevity signatures between the two strains, such as an upregulation of lipid storage and defense responses and downregulation of macromolecule synthesis and developmental processes. The shared longevity signatures revealed by metabolomics profiling included an increase in the levels of glycerol-3P, ademine, xanthine, and AMP, and a decrease in the levels of the amino acid pool, the C18:0 and C17:1 fatty acids. After we integrated transcriptomics and metabolomics data based on the annotations in KEGG, our results highlighted a downregulation of pyrimidine metabolism and upregulation of purine metabolism as a commonality between the two longevity mechanisms. Overall, our findings point towards the existence of shared metabolic pathways that are likely important for lifespan extension and provide novel insights into potential regulators and metabolic fingerprints for longevity.

biochemistry↗

bioRxiv2017

Fe2+/H2O2-mediated oxidation of homogentisic acid indicates the production of ochronotic and non-ochronotic pigments. Implications in Alkaptonuria and beyond.

Homogentisic acid (HGA) can be oxidized by a combination of Fe2+ and H2O2 into a darkly colored high molecular mass pigment. Increasing the concentration of H2O2 can lead to the formation of a high molecular mass material that exhibits less absorbance in the visible range of the electromagnetic spectrum, while maintaining a strong absorbance in the UV range of the electromagnetic spectrum. FT-IR spectroscopy did indicate the presence of a chemical feature in the pigments generated through H2O2-mediated oxidation that is absent in pigments generated through air-mediated oxidation. Our observations could have implications in the pathophysiology of alkaptonuria. In alkaptonuria, patients suffer from homogentisic aciduria from birth, but develop ochronosis (darkening) of collagenous tissues much later in life due to the formation of a melanin-like pigment. Three major questions regarding ochronosis remain to be answered: 1) how is the pigment formed, 2) why does it appear by the third decade of life and 3) why is it sporadic in appearance? Our results suggest that ochronotic or non-ochronotic pigments can be generated from HGA depending on the oxidation reaction conditions. Thus, the absence of any visible pigment, as for younger alkaptonuria patients, could not necessarily mean the absence of HGA-derived melanin-like molecules. We compare our results and their potential implications for ochronosis to the changes in pigmentation observed in vitiligo or aging (greying) hair.

biochemistry↗

bioRxiv2017

Modular assembly of the nucleolar large subunit processome

Early co-transcriptional events of eukaryotic ribosome assembly result in the formation of the small and large subunit processomes. We have determined cryo-EM reconstructions of the nucleolar large subunit processome in different conformational states at resolutions up to 3.4 [A]ngstroms. These structures reveal how steric hindrance and molecular mimicry are used to prevent premature folding states and binding of later factors. This is accomplished by the concerted activity of 21 ribosome assembly factors that stabilize and remodel pre-ribosomal RNA and ribosomal proteins. Mutually exclusive conformations of these particles suggest that the formation of the polypeptide exit tunnel is achieved through different folding pathways during subsequent stages of ribosome assembly.

biochemistry↗