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Rxivist combines preprints from bioRxiv with data from Twitter to help you find the papers being discussed in your field. Currently indexing 70,086 bioRxiv papers from 306,114 authors.

Most downloaded bioRxiv papers, since beginning of last month

in category biochemistry

2,032 results found. For more information, click each entry to expand.

1: A Compact Quadrupole-Orbitrap Mass Spectrometer with FAIMS Interface Improves Proteome Coverage in Short LC Gradients
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Posted to bioRxiv 30 Nov 2019

A Compact Quadrupole-Orbitrap Mass Spectrometer with FAIMS Interface Improves Proteome Coverage in Short LC Gradients
1,349 downloads biochemistry

Dorte B. Bekker-Jensen, Ana Martínez del Val, Sophia Steigerwald, Patrick Rüther, Kyle Fort, Tabiwang N Arrey, Alexander Harder, Alexander Makarov, Jesper V. Olsen

State-of-the-art proteomics-grade mass spectrometers can measure peptide precursors and their fragments with ppm mass accuracy at sequencing speeds of tens of peptides per second with attomolar sensitivity. Here we describe a compact and robust quadrupole-orbitrap mass spectrometer equipped with a front-end High Field Asymmetric Waveform Ion Mobility Spectrometry (FAIMS) Interface. The performance of the Orbitrap Exploris 480 mass spectrometer is evaluated in data-dependent acquisition (DDA) and data-independent acquisition (DIA) modes in combination with FAIMS. We demonstrate that different compensation voltages (CVs) for FAIMS are optimal for DDA and DIA, respectively. Combining DIA with FAIMS using single CVs, the instrument surpasses 2500 unique peptides identified per minute. This enables quantification of >5000 proteins with short online LC gradients delivered by the Evosep One LC system allowing acquisition of 60 samples per day. The raw sensitivity of the instrument is evaluated by analyzing 5 ng of a HeLa digest from which >1000 proteins were reproducibly identified with 5 minute LC gradients using DIA-FAIMS. To demonstrate the versatility of the instrument we recorded an organ-wide map of proteome expression across 12 rat tissues quantified by tandem mass tags and label-free quantification using DIA with FAIMS to a depth of >10,000 proteins.

2: A complex IRES at the 5'-UTR of a viral mRNA assembles a functional 48S complex via an uAUG intermediate.
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Posted to bioRxiv 04 Dec 2019

A complex IRES at the 5'-UTR of a viral mRNA assembles a functional 48S complex via an uAUG intermediate.
478 downloads biochemistry

Ritam Neupane, Vera P Pisareva, Carlos F. Rodríguez, Andrey V Pisarev, Israel S. Fernández

RNA viruses are pervasive entities in the biosphere with significant impact in human health and economically important livestock. As strict cellular parasites, RNA viruses abuse host resources, redirecting them towards viral replication needs. Taking control of the cellular apparatus for protein production is a requirement for virus progression and diverse strategies of cellular mimicry and/or ribosome hijacking evolved to ensure this control. Especially in complex eukaryotes, translation is a sophisticated process, with multiple mechanisms acting on ribosomes and mRNAs. The initiation stage of translation is specially regulated, involving multiple steps and the engagement of numerous initiation factors some of them of high complexity. The use of structured RNA sequences, called Internal Ribosomal Entry Sites (IRES), in viral RNAs is a widespread strategy for the exploitation of eukaryotic initiation. Using a combination of electron cryo-microscopy (cryo-EM) and reconstituted translation initiation assays with native components, we characterized how a novel IRES at the 5'-UTR of a viral RNA assembles a functional translation initiation complex via an uAUG intermediate, redirecting the cellular machinery for protein production towards viral messengers. The IRES features a novel extended, multi-domain architecture, circling the 40S head, leveraging ribosomal sites not previously described to be exploited by any IRES. The structures and accompanying functional data, illustrate the importance of 5'-UTR regions in translation regulation and underline the relevance of the untapped diversity of viral IRESs. Given the large number of new viruses metagenomic studies have uncovered, the quantity and diversity of mechanisms for translation hijacking encrypted in viral sequences may be seriously underestimated. Exploring this diversity could reveal novel avenues in the fight against these molecular pathogens.

3: Structure of the processive human Pol δ holoenzyme
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Posted to bioRxiv 11 Dec 2019

Structure of the processive human Pol δ holoenzyme
380 downloads biochemistry

Claudia Lancey, Muhammad Tehseen, Vlad-Stefan Raducanu, Fahad Rashid, Nekane Merino, Timothy J Ragan, Christos Savva, Manal S. Zaher, Afnan Shirbini, Francisco J. Blanco, Samir M. Hamdan, Alfredo De Biasio

In eukaryotes, DNA polymerase δ (Pol δ) bound to the proliferating cell nuclear antigen (PCNA) replicates the lagging strand and cooperates with flap endonuclease 1 (FEN1) to process the Okazaki fragments for their ligation. We present the high-resolution cryo-EM structure of the human processive Pol δ-DNA-PCNA complex in the absence and presence of FEN1. Pol δ is anchored to one of the three PCNA monomers through the C-terminal domain of the catalytic subunit. The catalytic core sits on top of PCNA in an open configuration while the regulatory subunits project laterally. This arrangement allows PCNA to thread and stabilize the DNA exiting the catalytic cleft and recruit FEN1 to one unoccupied monomer in a toolbelt fashion. Alternative holoenzyme conformations reveal important functional interactions that maintain PCNA orientation during synthesis. This work sheds light on the structural basis of Pol δ activity in replicating the human genome.

4: Machine Learning Predicts New Anti-CRISPR Proteins
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Posted to bioRxiv 29 Nov 2019

Machine Learning Predicts New Anti-CRISPR Proteins
331 downloads biochemistry

Simon Eitzinger, Amina Asif, Kyle E. Watters, Anthony T Iavarone, Gavin J. Knott, Jennifer A. Doudna, Fayyaz ul Amir Afsar Minhas

The increasing use of CRISPR-Cas9 in medicine, agriculture and synthetic biology has accelerated the drive to discover new CRISPR-Cas inhibitors as potential mechanisms of control for gene editing applications. Many such anti-CRISPRs have been found in mobile genetic elements that disable the CRISPR-Cas adaptive immune system. However, comparing all currently known anti-CRISPRs does not reveal a shared set of properties that can be used for facile bioinformatic identification of new anti-CRISPR families. Here, we describe AcRanker, a machine learning based method for identifying new potential anti-CRISPRs directly from proteomes using protein sequence information only. Using a training set of known anti-CRISPRs, we built a model based on XGBoost ranking and extensively benchmarked it through non-redundant cross-validation and external validation. We then applied AcRanker to predict candidate anti-CRISPRs from self-targeting bacterial genomes and discovered two previously unknown anti-CRISPRs: AcrllA16 (ML1) and AcrIIA17 (ML8). We show that AcrIIA16 strongly inhibits Streptococcus iniae Cas9 (SinCas9) and weakly inhibits Streptococcus pyogenes Cas9 (SpyCas9). We also show that AcrIIA17 inhibits both SpyCas9 and SauCas9 with low potency. The addition of AcRanker to the anti-CRISPR discovery toolkit allows researchers to directly rank potential anti-CRISPR candidate genes for increased speed in testing and validation of new anti-CRISPRs. A web server implementation for AcRanker is available online at http://acranker.pythonanywhere.com/.

5: Conserved function of ether lipids and sphingolipids in the early secretory pathway
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Posted to bioRxiv 19 Dec 2019

Conserved function of ether lipids and sphingolipids in the early secretory pathway
287 downloads biochemistry

Noemi Jiménez-Rojo, Manuel D. Leonetti, Valeria Zoni, Adai Colom, Suihan Feng, Namrata R. Iyengar, Stefan Matile, Aurélien Roux, Stefano Vanni, Jonathan S. Weissman, Howard Riezman

Sphingolipids have been shown to play important roles in physiology and cell biology, but a systematic examination of their functions is lacking. We performed a genome-wide CRISPRi screen in sphingolipid-depleted cells and identified hypersensitive mutants in genes of membrane trafficking and lipid biosynthesis, including ether lipid synthesis. Systematic lipidomic analysis showed a coordinate regulation of ether lipids with sphingolipids, where depletion of one of these lipid types resulted in increases in the other, suggesting an adaptation and functional compensation. Biophysical experiments on model membranes show common properties of these structurally diverse lipids that also share a known function as GPI anchors in different kingdoms of life. Molecular dynamics simulations show a selective enrichment of ether phosphatidylcholine around p24 proteins, which are receptors for the export of GPI-anchored proteins and have been shown to bind a specific sphingomyelin species. Our results support a model of convergent evolution of proteins and lipids, based on their physico-chemical properties, to regulate GPI-anchored protein transport and maintain homeostasis in the early secretory pathway.

6: A PI3K-WIPI2 positive feedback loop allosterically activates LC3 lipidation in autophagy
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Posted to bioRxiv 18 Dec 2019

A PI3K-WIPI2 positive feedback loop allosterically activates LC3 lipidation in autophagy
268 downloads biochemistry

Dorotea Fracchiolla, Chunmei Chang, James H. Hurley, Sascha Martens

Autophagy degrades cytoplasmic cargo by its delivery to lysosomes within double membrane autophagosomes. Synthesis of phosphoinositide PI(3)P by the autophagic PI 3-kinase complex I (PI3KC3-C1) and conjugation of ATG8/LC3 proteins to phagophore membranes by the ATG12–ATG5-ATG16L1 (E3) complex are two critical steps in autophagosome biogenesis, connected by WIPI2. Here we present a complete reconstitution of these events, recapitulating a considerable part of the human autophagy machinery. On giant unilamellar vesicles (GUVs), LC3 lipidation is strictly dependent on the recruitment of WIPI2, which in turn depends on PI(3)P. Ectopically targeting E3 to membranes in the absence of WIPI2 is insufficient to support LC3 lipidation, demonstrating that WIPI2 allosterically activates the E3 complex. PI3KC3-C1 and WIPI2 mutually promote the recruitment of each other in a positive feedback loop. When both PI 3-kinase and LC3 lipidation reactions were carried out simultaneously, positive feedback between PI3KC3-C1 and WIPI2 led to rapid LC3 lipidation with kinetics similar to those seen in cellular autophagosome formation. Summary Autophagy requires the synthesis of PI(3)P and the conjugation of LC3 to the phagophore membrane. We reconstituted these two reactions and their coupling by WIPI2, and showed that positive feedback between PI3KC3-C1 and WIPI2 leads to rapid LC3 lipidation by the ATG16L1 complex.

7: Improvement of cryo-EM maps by density modification
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Posted to bioRxiv 16 Nov 2019

Improvement of cryo-EM maps by density modification
268 downloads biochemistry

Thomas C. Terwilliger, Steven J Ludtke, Randy J. Read, Paul D. Adams, Pavel V. Afonine

A density modification procedure for improving maps produced by single-particle electron cryo-microscopy is presented. The theoretical basis of the method is identical to that of maximum-likelihood density modification, previously used to improve maps from macromolecular X-ray crystallography. Two key differences from applications in crystallography are that the errors in Fourier coefficients are largely in the phases in crystallography but in both phases and amplitudes in electron cryo-microscopy, and that half-maps with independent errors are available in electron cryo-microscopy. These differences lead to a distinct approach for combination of information from starting maps with information obtained in the density modification process. The applicability of density modification theory to electron cryo-microscopy was evaluated using half-maps for apoferritin at a resolution of 3.1 Å and a matched 1.8 Å reference map. Error estimates for the map obtained by density modification were found to closely agree with true errors as estimated by comparison with the reference map. The density modification procedure was applied to a set of 54 datasets where half-maps, a full map and a model all had been deposited. The procedure improved map-model correlation and increased the visibility of details in the maps. The procedure requires two unmasked half-maps and a sequence file or other source of information on the volume of the macromolecule that has been imaged.

8: Cryo-EM Structures and Regulation of Arabinofuranosyltransferase AftD from Mycobacteria
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Posted to bioRxiv 23 Dec 2019

Cryo-EM Structures and Regulation of Arabinofuranosyltransferase AftD from Mycobacteria
254 downloads biochemistry

Yong Zi Tan, Lei Zhang, José Rodrigues, Ruixiang Blake Zheng, Sabrina I. Giacometti, Ana L. Rosário, Brian Kloss, Venkata P Dandey, Hui Wei, Richard Brunton, Ashleigh Raczkowski, Diogo Athayde, Maria João Catalão, Madalena Pimentel, Oliver B Clarke, Todd L. Lowary, Margarida Archer, Michael Niederweis, Clinton S. Potter, Bridget Carragher, Filippo Mancia

Mycobacterium tuberculosis causes tuberculosis, a disease that kills over one million people each year. Its cell envelope is a common antibiotic target and has a unique structure due, in part, to two lipidated polysaccharides - arabinogalactan and lipoarabinomannan. Arabinofuranosyltransferase D (AftD) is an essential enzyme involved in assembling these glycolipids. We present the 2.9 Å resolution structure of M. abscessus AftD determined by single particle cryo-electron microscopy. AftD has a conserved GT-C glycosyltransferase fold and three carbohydrate binding modules. Glycan array analysis shows that AftD binds complex arabinose glycans. Additionally, AftD is non-covalently complexed with an acyl carrier protein (ACP). 3.4 and 3.5 Å structures of a mutant with impaired ACP binding reveal a conformational change that suggests the ACP may regulate AftD function. Using a conditional knock-out constructed in M. smegmatis, mutagenesis experiments confirm the essentiality of the putative active site and the ACP binding for AftD function.

9: Breaking a Strong Amide Bond: Structure and Properties of Dimethylformamidase
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Posted to bioRxiv 18 Dec 2019

Breaking a Strong Amide Bond: Structure and Properties of Dimethylformamidase
253 downloads biochemistry

Chetan Kumar Arya, Swati Yadav, Jonathan Fine, Ana Casanal, Gaurav Chopra, Gurunath Ramanathan, Kutti R Vinothkumar, Ramaswamy Subramanian

Dimethylformamidase (DMFase) breaks down the human-made synthetic solvent N,N -dimethyl formamide(DMF) used extensively in industry([1][1]). DMF is not known to exist in nature and was first synthesized in 1893. In spite of the recent origin of DMF certain bacterial species like Paracoccus, Pseudomonas , and Alcaligenes have evolved pathways to breakdown DMF and use them as carbon and nitrogen source for growth([2][2], [3][3]). The structure of DMFase from Paracoccus and the biochemical studies reported here provide a molecular basis for its stability, substrate specificity and catalysis. The structure reveals a multimeric complex of the α2β2 type or (α2β2)2 type. One of the three domains of the large subunit and the small subunit are hitherto undescribed folds and as yet of unknown evolutionary origin. The active site is made of a distinctive mononuclear iron that is coordinated by two tyrosine residues and a glutamic acid residue. The hydrolytic cleavage of the amide bond is catalyzed at the Fe3+ site with a proximal glutamate probably acting as the base. The change in the quaternary structure is salt dependent with high salt resulting in the larger oligomeric state. Kinetic characterization reveals an enzyme that shows cooperativity between subunits and the structure provides clues on the interconnection between the active sites. Significance Statement N,N -dimethyl formamide(DMF) is a commonly used industrial solvent that was first synthesized in 1893. The properties that make DMF a highly desired solvent also makes it a difficult compound to breakdown. Yet, certain bacteria have evolved to survive in environments polluted by DMF and have enzymes that breakdown DMF and use it as their carbon and nitrogen source. The molecular structure of the enzyme that breaks down the stable amide bond in these bacteria, reveals two new protein folds and a unique mononuclear iron active site. The work reported here provides the structural and biochemical framework to query the evolutionary origins of the protein, as well as in engineering this enzyme for use in bioremediation of a human made toxic solvent. [1]: #ref-1 [2]: #ref-2 [3]: #ref-3

10: O-GlcNAcylation of small heat shock proteins enhances their anti-amyloid chaperone activity
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Posted to bioRxiv 10 Dec 2019

O-GlcNAcylation of small heat shock proteins enhances their anti-amyloid chaperone activity
248 downloads biochemistry

Aaron T Balana, Paul M Levine, Somnath Mukherjee, Nichole J Pedowitz, Stuart P Moon, Terry T Takahashi, Christian F. W. Becker, Matthew R. Pratt

A major role for the intracellular posttranslational modification O-GlcNAc appears to be the inhibition of protein aggregation. Most of the previous studies in this area have focused on O-GlcNAcylation of the amyloid-forming proteins themselves. Here, we use synthetic protein chemistry to discover that O-GlcNAc also activates the anti-amyloid activity of certain small heat shock proteins (sHSPs), a potentially more important modification event that can act broadly and substoichiometrically. More specifically, we find that O-GlcNAcylation increases the ability of sHSPs to block the amyloid formation of both α-synuclein and Aβ. Mechanistically, we show that O-GlcNAc near the sHSP IXI-domain prevents its ability to intramolecularly compete with substrate binding. Our results have important implications for neurodegenerative diseases associated with amyloid formation and potentially other areas of sHSP biology.

11: α1A-adrenoceptor inverse agonists and agonists modulate receptor signalling through a conformational selection mechanism
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Posted to bioRxiv 07 Dec 2019

α1A-adrenoceptor inverse agonists and agonists modulate receptor signalling through a conformational selection mechanism
246 downloads biochemistry

Feng-Jie Wu, Lisa M Williams, Alaa Abdul-Ridha, Avanka Gunatilaka, Tasneem M Vaid, Martina Kocan, Alice R. Whitehead, Michael D.W. Griffin, Ross A.D. Bathgate, Daniel J. Scott, Paul R. Gooley

G-Protein Coupled Receptors (GPCRs) transmit signals across the cell membrane via an allosteric network from the ligand-binding site to the G-protein binding site via a series of conserved microswitches. Crystal structures of GPCRs provide snapshots of inactive and active states, but poorly describe the conformational dynamics of the allosteric network that underlies GPCR activation. Here we analyse the correlation between ligand binding and receptor conformation of the α1A-adrenoceptor, known for stimulating smooth muscle contraction in response to binding noradrenaline. NMR of 13CεH3-methionine labelled α1A-adrenoreceptor mutants, each exhibiting differing signalling capacities, revealed how different classes of ligands modulate receptor conformational equilibria. 13CεH3-methionine residues near the microswitches revealed distinct states that correlated with ligand efficacies, supporting a conformational selection mechanism. We propose that allosteric coupling between the microswitches controls receptor conformation and underlies the mechanism of ligand modulation of GPCR signalling in cells.

12: Cryo-EM Structure of the Fork Protection Complex Bound to CMG at a Replication Fork
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Posted to bioRxiv 19 Dec 2019

Cryo-EM Structure of the Fork Protection Complex Bound to CMG at a Replication Fork
244 downloads biochemistry

Domagoj Baretić, Michael Jenkyn-Bedford, Valentina Aria, Giuseppe Cannone, Mark Skehel, Joseph T.P. Yeeles

The eukaryotic replisome, organized around the Cdc45-MCM-GINS (CMG) helicase, orchestrates chromosome replication. Multiple factors associate directly with CMG including Ctf4 and the heterotrimeric fork protection complex (Csm3/Tof1 and Mrc1), that have important roles including aiding normal replication rates and stabilizing stalled forks. How these proteins interface with CMG to execute these functions is poorly understood. Here we present 3-3.5 Å resolution cryo-EM structures comprising CMG, Ctf4, Csm3/Tof1 and Mrc1 at a replication fork. The structures provide high-resolution views of CMG:DNA interactions, revealing the mechanism of strand separation. Furthermore, they illustrate the topology of Mrc1 in the replisome and show Csm3/Tof1 'grips' duplex DNA ahead of CMG via a network of interactions that are important for efficient replication fork pausing. Our work reveals how four highly conserved replisome components collaborate with CMG to facilitate replisome progression and maintain genome stability.

13: Native mass spectrometry can effectively predict PROTAC efficacy
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Posted to bioRxiv 25 Nov 2019

Native mass spectrometry can effectively predict PROTAC efficacy
237 downloads biochemistry

Rebecca Beveridge, Dirk Kessler, Klaus Rumpel, Peter Ettmayer, Anton Meinhart, Tim Clausen

Protein degraders, also known as proteolysis targeting chimeras (PROTACs), are bifunctional small molecules that bring an E3 ubiquitin ligase and a protein of interest (POI) into proximity, thus promoting ubiquitination and degradation of the targeted POI. Despite their great promise as next-generation pharmaceutical drugs, the development of new PROTACs is challenged by the complexity of the system, which involves binary and ternary interactions between components. Here, we demonstrate the strength of native mass spectrometry (nMS), a label-free technique, to provide novel insight into PROTAC-mediated protein interactions. We show that nMS can monitor the formation of ternary E3-PROTAC-POI complexes and detect various intermediate species in a single experiment. A unique benefit of the method is its ability to reveal preferentially formed E3-PROTAC-POI combinations in competition experiments with multiple substrate proteins, thereby positioning it as an ideal high-throughput screening strategy during the development of new PROTACs.

14: Crystal structure of a human plasma membrane phospholipid flippase
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Posted to bioRxiv 27 Dec 2019

Crystal structure of a human plasma membrane phospholipid flippase
235 downloads biochemistry

Hanayo Nakanishi, Katsumasa Irie, Katsumori Segawa, Kazuya Hasegawa, Yoshinori Fujiyoshi, Sigekazu Nagata, Kazuhiro Abe

ATP11C, a member of P4-ATPase flippase, exclusively translocates phosphatidylserine from the outer to the inner leaflets of the plasma membrane, and maintains the asymmetric distribution of phosphatidylserine in the living cell. However, the mechanisms by which ATP11C translocates phosphatidylserine remain elusive. Here we show the crystal structures of a human plasma membrane flippase, ATP11C-CDC50A complex, in an outward-open E2P conformation. Two phosphatidylserine molecules are in a conduit that continues from the cell surface to the occlusion site in the middle of the membrane. Mutations in either of the phosphotidylserine binding sites or along the pathway between significantly impairs specific ATPase and transport activities. We propose a model for phosphatidylserine translocation from the outer to the inner leaflet of the plasma membrane.

15: The α-synuclein hereditary mutation E46K unlocks a more stable, pathogenic fibril structure
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Posted to bioRxiv 08 Dec 2019

The α-synuclein hereditary mutation E46K unlocks a more stable, pathogenic fibril structure
234 downloads biochemistry

David R. Boyer, Binsen Li, Chuanqi Sun, Weijia Fan, Kang Zhou, Michael P. Hughes, Michael R. Sawaya, Lin Jiang, David S. Eisenberg

Aggregation of α-synuclein is a defining molecular feature of Parkinson's disease, Lewy Body Dementia, and Multiple Systems Atrophy. Hereditary mutations in α-synuclein are linked to both Parkinson's disease and Lewy Body Dementia; in particular, patients bearing the E46K disease mutation manifest a clinical picture of parkinsonism and Lewy Body Dementia, and E46K creates more pathogenic fibrils in vitro. Understanding the effect of these hereditary mutations on α-synuclein fibril structure is fundamental to α-synuclein biology. We therefore determined the cryoEM structure of α-synuclein fibrils containing the hereditary E46K mutation. The 2.5 Å structure reveals a symmetric double protofilament in which the molecules adopt a vastly re-arranged, lower energy fold compared to wild-type fibrils. We propose that the E46K misfolding pathway avoids electrostatic repulsion between K46 and K80, a residue pair which forms the E46-K80 salt-bridge in the wild-type fibril structure. We hypothesize that under our conditions the wild-type fold does not reach this deeper energy well of the E46K fold because the E46-K80 salt bridge diverts α-synuclein into a kinetic trap – a shallower, more accessible energy minimum. The E46K mutation apparently unlocks a more stable and pathogenic fibril structure.

16: Microtubule Nucleation by Single Human γTuRC in a Partly Open Asymmetric Conformation
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Posted to bioRxiv 23 Nov 2019

Microtubule Nucleation by Single Human γTuRC in a Partly Open Asymmetric Conformation
220 downloads biochemistry

Tanja Consolati, Julia Locke, Johanna Roostalu, Jayant Asthana, Wei Ming Lim, Julian Gannon, Fabrizio Martino, Alessandro Costa, Thomas Surrey

The γ-tubulin ring complex (γTuRC) is the major microtubule nucleator in cells. However, the mechanism of its regulation is not understood. Here, we purified human γTuRC and quantitatively characterized its nucleation properties in a TIRF microscopy-based real-time nucleation assay. We find that microtubule nucleation by γTuRC is kinetically inhibited compared to microtubule elongation. Determining the cryo-EM structure of γTuRC at 4 Å resolution reveals an asymmetric conformation with only part of the complex in a 'closed' conformation matching the microtubule geometry. Several factors stabilise the closed conformation. One is actin in the core of the complex and others, likely MZT1 or MZT2, line the outer perimeter of the closed part of γTuRC. The opposed side of γTuRC is in an 'open', nucleation-incompetent conformation, leading to a structural asymmetry, explaining the kinetic inhibition of nucleation by human γTuRC. Our data suggest possible regulatory mechanisms for microtubule nucleation by γTuRC closure.

17: Hierarchical assembly of the MLL1 core complex within a biomolecular condensate regulates H3K4 methylation
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Posted to bioRxiv 10 Dec 2019

Hierarchical assembly of the MLL1 core complex within a biomolecular condensate regulates H3K4 methylation
205 downloads biochemistry

Kevin E.W. Namitz, Song Tan, Michael S. Cosgrove

The enzymes that regulate histone H3 lysine 4 (H3K4) methylation are required for cellular differentiation and development and are often mutated in human disease. Mixed Lineage Leukemia protein-1 (MLL1) is a member of the SET1 family of histone H3 lysine 4 methyltransferases, which require interaction with a conserved sub-complex consisting of WDR5, RbBP5, Ash2L and DPY30 (WRAD2) for maximal activity. It is currently unclear how assembly of SET1 family complexes is involved in the spatiotemporal control of H3K4 methylation in eukaryotic genomes. In this investigation, we systematically characterized the hydrodynamic and kinetic properties of a reconstituted human MLL1 core complex and found that its assembly is highly concentration and temperature dependent. Consistent with a hierarchical assembly pathway, we found that the holo-complex assembles through interactions between the MW and RAD2 sub-complexes, which is correlated with enzymatic activity. Surprisingly, we found that the disassembled state is favored at physiological temperatures, and that this thermodynamic barrier can be overcome under conditions that induce high-local concentrations of subunits in phase separated compartments. Combining this data with the observation that MLL1 primary sequence contains large regions of intrinsic disorder, we propose a swinging-domain model in which the interaction between a tethered MW subcomplex and multiple nucleosome-RAD2 complexes is regulated by the rapid formation or dissolution of biomolecular condensates, such as occurs in transcription factories. This model provides an elegant switch-like mechanism for spatiotemporal control of H3K4 methylation within eukaryotic genomes.

18: Aequorea victoria’s secrets
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Posted to bioRxiv 19 Jun 2019

Aequorea victoria’s secrets
202 downloads biochemistry

Talley Lambert, Hadrien Depernet, Guillaume Gotthard, V. Raicu, Isabelle Navizet, Daphne S. Bindels, Vincent Levesque, Jennifer N. Moffatt, Anya Salih, Antoine Royant, Nathan C. Shaner

Using mRNA-Seq and de novo transcriptome assembly, we identified, cloned and characterized nine previously undiscovered fluorescent protein (FP) homologs from Aequorea victoria and a related Aequorea species, with most sequences highly divergent from avGFP. Among these FPs are the brightest GFP homolog yet characterized and a reversibly photochromic FP that responds to UV and blue light. Beyond green emitters, Aequorea species express purple- and blue-pigmented chromoproteins (CPs) with absorbances ranging from green to far-red, including two that are photoconvertible. X-ray crystallography revealed that Aequorea CPs contain a chemically novel chromophore with an unexpected crosslink to the main polypeptide chain. Because of the unique attributes of several of these newly discovered FPs, we expect that Aequorea will, once again, give rise to an entirely new generation of useful probes for bioimaging and biosensing.

19: A simple approach for accurate peptide quantification in MS-based proteomics
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Posted to bioRxiv 16 Jul 2019

A simple approach for accurate peptide quantification in MS-based proteomics
201 downloads biochemistry

Teresa Mendes Maia, An Staes, Kim Plasman, Jarne Pauwels, Katie Boucher, Andrea Argentini, Lennart Martens, Tony Montoye, Kris Gevaert, Francis Impens

Despite its growing popularity and use, bottom-up proteomics remains a complex analytical methodology. Its general workflow consists of three main steps: sample preparation, liquid chromatography coupled to tandem mass spec-trometry (LC-MS/MS) and computational data analysis. Quality assessment of the different steps and components of this workflow is instrumental to identify technical flaws and to avoid loss of precious measurement time and sample material. However, assessment of the extent of sample losses along the sample preparation protocol, in particular after proteolytic digestion, is not yet routinely implemented because of the lack of an accurate and straightforward method to quantify peptides. Here, we report on the use of a microfluidic UV/visible spectrophotometer to quantify MS-ready peptides directly in MS loading solvent, consuming only 2 microliter of sample. We determined the optimal peptide amount for LC-MS/MS analysis on a Q Exactive HF mass spectrometer using a dilution series of a commercial K562 cell digest. Careful evaluation of selected LC and MS parameters allowed us to define 3 microgram as an optimal peptide amount to be injected on this particular LC-MS/MS system. Finally, using tryptic digests from human HEK293T cells, we showed that injecting equal peptide amounts, rather than approximated ones, results into less variable LC-MS/MS and protein quantification data. The obtained quality improvement together with easy implementation of the ap-proach makes it possible to routinely quantify MS-ready peptides as a next step in daily proteomics quality control.

20: Monoubiquitination by the Fanconi Anemia core complex locks FANCI:FANCD2 on DNA in filamentous arrays
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Posted to bioRxiv 03 Dec 2019

Monoubiquitination by the Fanconi Anemia core complex locks FANCI:FANCD2 on DNA in filamentous arrays
184 downloads biochemistry

Winnie Tan, Sylvie van Twest, Andrew Leis, Rohan Bythell-Douglas, Vincent J. Murphy, Michael Sharp, Michael W Parker, Wayne M Crismani, Andrew J. Deans

FANCI:FANCD2 monoubiquitination is a critical event for replication fork stabilization by the Fanconi anemia (FA) DNA repair pathway. It has been proposed that at stalled replication forks, monoubiquitinated-FANCD2 serves to recruit DNA repair proteins that contain ubiquitin-binding motifs. Here we have reconstituted the FA pathway in vitro to study functional consequences of FANCI:FANCD2 monoubiquitination. We report that monoubiquitination does not promote any specific exogenous protein:protein interactions, but instead stabilizes FANCI:FANCD2 heterodimers on dsDNA. This locking of FANCI:FANCD2 complex on DNA requires monoubiquitination of only the FANCD2 subunit. We further show that purified monoubiquitinated FANCI:FANCD2 forms filament-like arrays on long dsDNA using electron microscopy. Our results reveal how monoubiquitinated FANCI:FANCD2 is activated upon DNA binding and present new insights to potentially modulate monoubiquitinated FANCI:FANCD2/DNA filaments in FA cells.

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