Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 93,254 bioRxiv papers from 397,991 authors.
Most downloaded bioRxiv papers, all time
in category biochemistry
3,091 results found. For more information, click each entry to expand.
2,160 downloads biochemistry
Protein phosphorylation is a ubiquitous post-translational modification (PTM) that regulates all aspects of life. To date, investigation of human cell signalling has focussed on canonical phosphorylation of serine (Ser), threonine (Thr) and tyrosine (Tyr) residues. However, mounting evidence suggests that phosphorylation of histidine also plays a central role in regulating cell biology. Phosphoproteomics workflows rely on acidic conditions for phosphopeptide enrichment, which are incompatible with the analysis of acid-labile phosphorylation such as histidine. Consequently, the extent of non-canonical phosphorylation is likely to be under-estimated. We report an Unbiased Phosphopeptide enrichment strategy based on Strong Anion Exchange (SAX) chromatography (UPAX), which permits enrichment of acid-labile phosphopeptides for characterisation by mass spectrometry. Using this approach, we identify extensive and positional phosphorylation patterns on histidine, arginine, lysine, aspartate and glutamate in human cell extracts, including 310 phosphohistidine and >1000 phospholysine sites of protein modification. Remarkably, the extent of phosphorylation on individual non-canonical residues vastly exceeds that of basal phosphotyrosine. Our study reveals the previously unappreciated diversity of protein phosphorylation in human cells, and opens up avenues for exploring roles of acid-labile phosphorylation in any proteome using mass spectrometry.
2,143 downloads biochemistry
Christiane Iserman, Christine Roden, Mark Boerneke, Rachel Sealfon, Grace McLaughlin, Irwin Jungreis, Christopher Y. Park, Avinash Boppana, Ethan Fritch, Yixuan J. Hou, Chandra Theesfeld, Olga G. Troyanskaya, Ralph S. Baric, Timothy P. Sheahan, Kevin Weeks, Amy S. Gladfelter
A mechanistic understanding of the SARS-CoV-2 viral replication cycle is essential to develop new therapies for the COVID-19 global health crisis. In this study, we show that the SARS-CoV-2 nucleocapsid protein (N-protein) undergoes liquid-liquid phase separation (LLPS) with the viral genome, and propose a model of viral packaging through LLPS. N-protein condenses with specific RNA sequences in the first 1000 nts (5'-End) under physiological conditions and is enhanced at human upper airway temperatures. N-protein condensates exclude non-packaged RNA sequences. We comprehensively map sites bound by N-protein in the 5'-End and find preferences for single-stranded RNA flanked by stable structured elements. Liquid-like N-protein condensates form in mammalian cells in a concentration-dependent manner and can be altered by small molecules. Condensation of N-protein is sequence and structure specific, sensitive to human body temperature, and manipulatable with small molecules thus presenting screenable processes for identifying antiviral compounds effective against SARS-CoV-2. ### Competing Interest Statement K.M.W. is an advisor to and holds equity in Ribometrix, to which mutational profiling (MaP) technologies have been licensed. All other authors declare that they have no competing interests.
2,140 downloads biochemistry
The ongoing Corona Virus Disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2), has emphasized the urgent need for antiviral therapeutics. The viral RNA-dependent-RNA-polymerase (RdRp) is a promising target with polymerase inhibitors successfully used for the treatment of several viral diseases. Here we show that Favipiravir exerts an antiviral effect as a nucleotide analogue through a combination of chain termination, slowed RNA synthesis and lethal mutagenesis. The SARS-CoV RdRp complex is at least 10-fold more active than any other viral RdRp known. It possesses both unusually high nucleotide incorporation rates and high-error rates allowing facile insertion of Favipiravir into viral RNA, provoking C-to-U and G-to-A transitions in the already low cytosine content SARS-CoV-2 genome. The coronavirus RdRp complex represents an Achilles heel for SARS-CoV, supporting nucleoside analogues as promising candidates for the treatment of COVID-19. ### Competing Interest Statement The authors have declared no competing interest.
2,139 downloads biochemistry
Eschericia coli remains the workhorse producing recombinant proteins given its ease of handling, access and genetic manipulation using standard laboratory techniques. However, disulfide-rich proteins can be difficult to produce in E. coli, in large part due to the reducing environment of the bacterial cytoplasm. Refolding from insoluble inclusion bodies can be a viable strategy for generating substantial quantities of disulfide-rich protein. For the best chance of successfully refolding a protein, it is vital to carry out a variety of small-scale test refolds under a swathe of conditions including altering the concentration of urea, salts, reduced and oxidized glutathione, temperature, length of refold time and protein dilution factor. Once a protein has undergone refolding it is vital to determine that the final product is natively folded given the chance of soluble misfolded protein. For determination of correct folding, a variety of techniques can be employed, and ideally, numerous should be used together. For proteins that possess enzymatic function the gold standard to assess correct folding is an activity assay. Non-enzymatic proteins can be assessed using a combination of circular dichroism and nuclear magnetic resonance spectroscopy. These techniques should be utilized alongside mass spectrometry, Western blotting and SDS-PAGE.
2,134 downloads biochemistry
Stress granules are condensates of non-translating mRNAs and proteins involved in the stress response and neurodegenerative diseases. Stress granules form in part through intermolecular RNA-RNA interactions, although the process of RNA condensation is poorly understood. In vitro , we demonstrate that RNA is effectively recruited to the surfaces of RNA or RNP condensates. We demonstrate that the DEAD-box protein eIF4A reduces RNA condensation in vitro and limits stress granule formation in cells. This defines a purpose for eIF4A to limit intermolecular RNA-RNA interactions in cells, thereby allowing for proper RNP function. These results establish an important role for DEAD-box proteins as ATP-dependent RNA chaperones that can limit the intermolecular condensation and entanglement of RNA, analogous to the function of proteins like HSP70 in combatting protein aggregates. eTOC Blurb Stress granules are formed in part by the process of RNA condensation, which is mediated by and promotes trans RNA-RNA interactions. The essential DEAD-box protein and translation initiation factor eIF4A limits stress granule formation by reducing RNA condensation through its function as an ATP-dependent RNA binding protein, behaving analogously to how protein chaperones like HSP70 combat protein aggregates. Highlights
2,118 downloads biochemistry
To further integrate mass spectrometry (MS)-based proteomics into biomedical research and especially into clinical settings, high throughput and robustness are essential requirements. They are largely met in high-flow rate chromatographic systems for small molecules but these are not sufficiently sensitive for proteomics applications. Here we describe a new concept that delivers on these requirements while maintaining the sensitivity of current nano-flow LC systems. Low-pressure pumps elute the sample from a disposable trap column, simultaneously forming a chromatographic gradient that is stored in a long storage loop. An auxiliary gradient creates an offset, ensuring the re-focusing of the peptides before the separation on the analytical column by a single high-pressure pump. This simplified design enables robust operation over thousands of sample injections. Furthermore, the steps between injections are performed in parallel, reducing overhead time to a few minutes and allowing analysis of more than 200 samples per day. From fractionated HeLa cell lysates, deep proteomes covering more than 130,000 sequence unique peptides and close to 10,000 proteins were rapidly acquired. Using this data as a library, we demonstrate quantitation of 5200 proteins in only 21 min. Thus, the new system - termed Evosep One - analyzes samples in an extremely robust and high throughput manner, without sacrificing in depth proteomics coverage.
2,113 downloads biochemistry
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of coronavirus disease 2019 (COVID-19). The rapid, sensitive and specific diagnosis of SARS-CoV-2 by fast and unambiguous testing is widely recognized to be critical in responding the current outbreak. Since the current testing capacity by conventional PCR based methods is insufficient because of shortages of supplies such as RNA extraction kits and PCR reagents, alternative and/or complementary testing assays should be developed. Here, we exploit the potential of targeted mass spectrometry based proteomic technologies to solve the current issue of insufficient SARS-CoV-2 diagnostic testing capacity. We have assessed the limit of detection by parallel reaction monitoring (PRM) on an Orbitrap Eclipse mass spectrometer for target tryptic peptides of several SARS-CoV-2 proteins from a sample of virus infected Vero cells. For Nucleocapsid protein the limit of detection was found to be in the mid-attomole range (0.9 x 10-12 g), which would theoretically correspond to approximately 10,000 SARS-CoV-2 particles, under the assumption that all viral proteins are assembled in macromolecular virus particles. Whether or not this sensitivity is sufficient to play a role in SARS-CoV-2 detection in patient material such as swabs or body fluids largely depends on the amount of viral proteins present in such samples and is subject of further research. If yes, mass spectrometry based methods could serve as a complementary protein based diagnostic tool and further steps should be focused on sample preparation protocols and on improvements in sample throughput. ### Competing Interest Statement The authors have declared no competing interest.
2,108 downloads biochemistry
MicroRNAs (miRNAs) act within Argonaute proteins to guide repression of mRNA targets. Although various approaches have provided insight into target recognition, the sparsity of miRNA–target affinity measurements has limited understanding and prediction of targeting efficacy. Here, we adapted RNA bind-n-seq to enable measurement of relative binding affinities between Argonaute–miRNA complexes and all ≤12-nucleotide sequences. This approach revealed noncanonical target sites unique to each miRNA, miRNA-specific differences in canonical target-site affinities, and a 100-fold impact of dinucleotides flanking each site. These data enabled construction of a biochemical model of miRNA-mediated repression, which was extended to all miRNA sequences using a convolutional neural network. This model substantially improved prediction of cellular repression, thereby providing a biochemical basis for quantitatively integrating miRNAs into gene-regulatory networks.
2,107 downloads biochemistry
The pandemic of SARS-CoV-2 has caused a high number of deaths in the world. To combat it, it is necessary to develop a better understanding of how the virus infects host cells. Infection normally starts with the attachment of the virus to cell-surface glycans like heparan sulfate (HS) and sialic acid-containing oligosaccharides. In this study, we examined and compared the binding of the subunits and spike (S) proteins of SARS-CoV-2 and SARS-CoV, MERS-CoV to these glycans. Our results revealed that the S proteins and subunits can bind to HS in a sulfation-dependent manner, the length of HS is not a critical factor for the binding, and no binding with sialic acid residues was detected. Overall, this work suggests that HS binding may be a general mechanism for the attachment of these coronaviruses to host cells, and supports the potential importance of HS in infection and in the development of antiviral agents against these viruses. ### Competing Interest Statement The authors have declared no competing interest.
2,105 downloads biochemistry
We present an algorithm for automatic map sharpening that is based on optimization of detail and connectivity of the sharpened map. The detail in the map is reflected in the surface area of an iso-contour surface that contains a fixed fraction of the volume of the map, where a map with high level of detail has a high surface area. The connectivity of the sharpened map is reflected in the number of connected regions defined by the same iso-contour surfaces, where a map with high connectivity has a small number of connected regions. By combining these two measures in a metric we term adjusted surface area, we can evaluate map quality in an automated fashion. We use this metric to choose optimal map sharpening parameters without reference to a model or other interpretations of the map. Map sharpening by optimization of adjusted surface area can be carried out for a map as a whole or it can be carried out locally, yielding a locally-sharpened map. To evaluate the performance of various approaches, we use a simple metric based on map-model correlation that can reproduce visual choices of optimally-sharpened maps. The map-model correlation is calculated using a model with B-factors (atomic displacement factors, ADP) set to zero. We use this model-based metric to evaluate map sharpening, use it to evaluate map sharpening approaches and find that optimization of adjusted surface area can be an effective tool for map sharpening.
2,050 downloads biochemistry
Severe acute respiratory syndrome-related coronavirus 2 (SARS-CoV-2) has resulted in a pandemic and continues to spread around the globe at an unprecedented rate. To date, no effective therapeutic is available to fight its associated disease, COVID-19. Our discovery of a novel insertion of glycosaminoglycan (GAG)-binding motif at S1/S2 proteolytic cleavage site (681-686 (PRRARS)) and two other GAG-binding-like motifs within SARS-CoV-2 spike glycoprotein (SGP) led us to hypothesize that host cell surface GAGs might be involved in host cell entry of SARS-CoV-2. Using a surface plasmon resonance direct binding assay, we found that both monomeric and trimeric SARS-CoV-2 spike more tightly bind to immobilized heparin (KD = 40 pM and 73 pM, respectively) than the SARS-CoV and MERS-CoV SGPs (500 nM and 1 nM, respectively). In competitive binding studies, the IC50 of heparin, tri-sulfated non-anticoagulant heparan sulfate, and non-anticoagulant low molecular weight heparin against SARS-CoV-2 SGP binding to immobilized heparin were 0.056 μM, 0.12 μM, and 26.4 μM, respectively. Finally, unbiased computational ligand docking indicates that heparan sulfate interacts with the GAG-binding motif at the S1/S2 site on each monomer interface in the trimeric SARS-CoV-2 SGP, and at another site (453-459 (YRLFRKS)) when the receptor-binding domain is in an open conformation. Our study augments our knowledge in SARS-CoV-2 pathogenesis and advances carbohydrate-based COVID-19 therapeutic development. ### Competing Interest Statement The authors have declared no competing interest.
1,988 downloads biochemistry
The use of CRISPR-Cas9 as a therapeutic reagent is hampered by its off-target effects. Although rationally designed S. pyogenes Cas9 (SpCas9) variants that display higher specificities than the wild-type SpCas9 protein are available, these attenuated Cas9 variants are often poorly efficient in human cells. Here, we have used a directed evolution approach in E. coli to obtain Sniper-Cas9, which shows high specificities without sacrificing on-target activities in human cells.
1,984 downloads biochemistry
Transcription of eukaryotic protein-coding genes requires passage of RNA polymerase II (Pol II) through chromatin. Pol II passage is impaired by nucleosomes and requires elongation factors that help Pol II to efficiently overcome the nucleosomal barrier. How the Pol II machinery transcribes through a nucleosome remains unclear because structural studies have been limited to Pol II elongation complexes formed on DNA templates lacking nucleosomes. Here we report the cryo-electron microscopy (cryo-EM) structure of transcribing Pol II from the yeast Saccharomyces cerevisiae engaged with a downstream nucleosome core particle (NCP) at an overall resolution of 4.4 Angstrom. Pol II and the NCP adopt a defined orientation that could not be predicted from modelling. Pol II contacts DNA of the incoming NCP on both sides of the nucleosomal dyad with its domains "clamp head" and "lobe". Comparison of the Pol II-NCP structure to known structures of Pol II complexes reveals that the elongation factors TFIIS, DSIF, NELF, PAF1 complex, and SPT6 can all be accommodated in the presence of the oriented nucleosome. Further structural comparisons show that the chromatin remodelling enzyme Chd1, which is also required for efficient Pol II passage, could bind the oriented nucleosome with its motor domain. The DNA-binding region of Chd1 must however be released from DNA when Pol II approaches the nucleosome, and based on published data this is predicted to stimulate Chd1 activity and to facilitate Pol II passage. Our results provide a starting point for a mechanistic analysis of chromatin transcription.
1,984 downloads biochemistry
Kinases play a critical role in many cellular signaling pathways and are dysregulated in a number of diseases, such as cancer, diabetes, and neurodegeneration. Since the FDA approval of imatinib in 2001, therapeutics targeting kinases now account for roughly 50% of current cancer drug discovery efforts. The ability to explore human kinase biochemistry, biophysics, and structural biology in the laboratory is essential to making rapid progress in understanding kinase regulation, designing selective inhibitors, and studying the emergence of drug resistance. While insect and mammalian expression systems are frequently used for the expression of human kinases, bacterial expression systems are superior in terms of simplicity and cost-effectiveness but have historically struggled with human kinase expression. Following the discovery that phosphatase coexpression could produce high yields of Src and Abl kinase domains in bacterial expression systems, we have generated a library of 52 His-tagged human kinase domain constructs that express above 2 μg/mL culture in a simple automated bacterial expression system utilizing phosphatase coexpression (YopH for Tyr kinases, Lambda for Ser/Thr kinases). Here, we report a structural bioinformatics approach to identify kinase domain constructs previously expressed in bacteria likely to express well in a simple high-throughput protocol, experiments demonstrating our simple construct selection strategy selects constructs with good expression yields in a test of 84 potential kinase domain boundaries for Abl, and yields from a high-throughput expression screen of 96 human kinase constructs. Using a fluorescence-based thermostability assay and a fluorescent ATP-competitive inhibitor, we show that the highest-expressing kinases are folded and have well-formed ATP binding sites. We also demonstrate how the resulting expressing constructs can be used for the biophysical and biochemical study of clinical mutations by engineering a panel of 48 Src mutations and 46 Abl mutations via single-primer mutagenesis and screening the resulting library for expression yields. The wild-type kinase construct library is available publicly via Addgene, and should prove to be of high utility for experiments focused on drug discovery and the emergence of drug resistance.
1,976 downloads biochemistry
Diverse RNAs and RNA-binding proteins form phase-separated, membraneless granules in cells under stress conditions. However, the role of the prevalent mRNA methylation, m6A, and its binding proteins in stress granule (SG) assembly remain unclear. Here, we show that m6A-modified mRNAs are enriched in SGs, and that m6A-binding YTHDF proteins are critical for SG formation. Depletion of YTHDF1/3 inhibits SG formation and recruitment of m6A-modified mRNAs to SGs. Both the N-terminal intrinsically disordered region and the C-terminal m6A-binding YTH domain of YTHDF proteins are crucial for SG formation. Super-resolution imaging further reveals that YTHDF proteins are in a super-saturated state, forming clusters that reside in the periphery of and at the junctions between SG core clusters, and promote SG phase separation by reducing the activation energy barrier and critical size for condensate formation. Our results reveal a new function and mechanistic insights of the m6A-binding YTHDF proteins in regulating phase separation.
1,971 downloads biochemistry
The simple bimolecular ligand-receptor binding interaction is often linearized by assuming pseudo-first-order kinetics when one species is present in excess. Here, a phase-plane analysis allows the derivation of a new condition for the validity of pseudo-first-order kinetics that is independent of the initial receptor concentration. The validity of the derived condition is analyzed from two viewpoints. In the first, time courses of the exact and approximate solutions to the ligand--receptor rate equations are compared when all rate constants are known. The second viewpoint assess the validity through the error induced when the approximate equation is used to estimate kinetic constants from data. Although these two interpretations of validity are often assumed to coincide, we show that they are distinct, and that large errors are possible in estimated kinetic constants, even when the linearized and exact rate equations provide nearly identical solutions.
1,967 downloads biochemistry
Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the Coronavirus disease 2019 (COVID-19) which is currently negatively affecting the population and disrupting the global economy. SARS-CoV-2 belongs to the +RNA virus family that utilize single-stranded positive-sense RNA molecules as genomes. SARS-CoV-2, like other coronaviruses, has an unusually large genome for a +RNA virus that encodes four structural proteins - the matrix (M), small envelope (E), spike (S) and nucleocapsid phosphoprotein (N) - and sixteen nonstructural proteins (nsp1-16) that together ensure replication of the virus in the host cell. The nucleocapsid phosphoprotein N is essential for linking the viral genome to the viral membrane. Its N-terminal RNA binding domain (N-NTD) captures the RNA genome while the C-terminal domain anchors the ribonucleoprotein complex to the viral membrane via its interaction with the M protein. Here, we characterized the structure of the N-NTD and its interaction with RNA using NMR spectroscopy. We observed a positively charged canyon on the surface of the N-NTD lined with arginine residues suggesting a putative RNA binding site. Next, we performed an NMR titration experiment using an RNA duplex. The observed changes in positions of signals in the N-NTD NMR spectra allowed us to construct a model of the N-NTD in complex with RNA.
1,955 downloads biochemistry
Daniel Dominguez, Peter Freese, Maria Alexis, Amanda Su, Myles Hochman, Tsultrim Palden, Cassandra Bazile, Nicole J Lambert, Eric L Van Nostrand, Gabriel A Pratt, Gene W Yeo, Brenton R. Graveley, Christopher B. Burge
Production of functional cellular RNAs requires multiple processing steps principally mediated by RNA binding proteins (RBPs). Here we present the affinity landscape of 78 human RNA binding proteins using an unbiased assay that determines the sequence, structure, and context preferences of RBPs from a diverse RNA pool. The importance of RBP specificities in regulation of RNA processing is shown through integrative analysis with in vivo binding and loss of function studies. While we find that many proteins bind similar short sequence elements, specificities across factors diverge when additional features such as secondary structure, bipartite motifs and nucleotide context are considered. These data present a more comprehensive view of how RBPs bind their targets, a central requirement for understanding RNA processing mechanisms and outcomes.
1,922 downloads biochemistry
Proteins smaller than about 50 kDa are currently too small to be imaged by cryo-electron microscopy (cryo-EM), leaving most protein molecules in the cell beyond the reach of this powerful structural technique. Here we use a designed protein scaffold to bind and symmetrically display 12 copies of a small 26 kDa protein. We show that the bound cargo protein is held rigidly enough to visualize it at a resolution of 3.8 Å by cryo-EM, where basic structural features of the protein are visible. The designed scaffold is modular and can be modified through modest changes in its amino acid sequence to bind and display diverse proteins for imaging, thus providing a general method to break through the lower size limitation in cryo-EM.
1,919 downloads biochemistry
Oligonucleotide-guided nucleases (OGNs) have enabled rapid advances in precision genome engineering. Though much effort has gone into characterizing and mitigating mismatch tolerance for the most widely adopted OGN, Streptococcus pyogenes Cas9 (SpCas9), potential off-target interactions may still limit applications where on-target specificity is critical. Here we present a new axis to control mismatch sensitivity along the recognition-conferring spacer sequence of SpCas9's guide RNA (gRNA). We introduce mismatch-evading lowered-thermostability guides (melt-guides) and exhibit how nucleotide-type substitutions in the spacer can reduce cleavage of sequences mismatched by as few as a single base pair. Co-transfecting melt-guides into human cell culture with an exonuclease involved in DNA repair, we observe indel formation on a standard genomic target at approximately 70% the rate of canonical gRNA and undetectable on off-target data.
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