Nature Structural & Molecular Biology最新文献

{"title":"Resolving chaperone-assisted protein folding on the ribosome at the peptide level","authors":"Thomas E. Wales, Aleksandra Pajak, Alžběta Roeselová, Santosh Shivakumaraswamy, Steven Howell, Svend Kjær, F. Ulrich Hartl, John R. Engen, David Balchin","doi":"10.1038/s41594-024-01355-x","DOIUrl":"10.1038/s41594-024-01355-x","url":null,"abstract":"Protein folding in vivo begins during synthesis on the ribosome and is modulated by molecular chaperones that engage the nascent polypeptide. How these features of protein biogenesis influence the maturation pathway of nascent proteins is incompletely understood. Here, we use hydrogen–deuterium exchange mass spectrometry to define, at peptide resolution, the cotranslational chaperone-assisted folding pathway of Escherichia coli dihydrofolate reductase. The nascent polypeptide folds along an unanticipated pathway through structured intermediates not populated during refolding from denaturant. Association with the ribosome allows these intermediates to form, as otherwise destabilizing carboxy-terminal sequences remain confined in the ribosome exit tunnel. Trigger factor binds partially folded states without disrupting their structure, and the nascent chain is poised to complete folding immediately upon emergence of the C terminus from the exit tunnel. By mapping interactions between the nascent chain and ribosomal proteins, we trace the path of the emerging polypeptide during synthesis. Our work reveals new mechanisms by which cellular factors shape the conformational search for the native state. The authors follow the folding dynamics of a nascent protein trapped during its synthesis, showing how the ribosome and a molecular chaperone shape the pathway of protein folding.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 12","pages":"1888-1897"},"PeriodicalIF":12.5,"publicationDate":"2024-07-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41594-024-01355-x.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141577168","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"AlphaFold3 takes a step toward decoding molecular behavior and biological computation","authors":"Rohit Roy, Hashim M. Al-Hashimi","doi":"10.1038/s41594-024-01350-2","DOIUrl":"10.1038/s41594-024-01350-2","url":null,"abstract":"AlphaFold 3 represents a breakthrough in predicting the 3D structures of complexes directly from their sequences, offering insights into biomolecular interactions. Extending predictions to molecular behavior and function requires a shift from viewing biomolecules as static 3D structures to dynamic conformational ensembles.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 7","pages":"997-1000"},"PeriodicalIF":12.5,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141556979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"VCP/p97-associated proteins are binders and debranching enzymes of K48–K63-branched ubiquitin chains","authors":"Sven M. Lange, Matthew R. McFarland, Frederic Lamoliatte, Thomas Carroll, Logesvaran Krshnan, Anna Pérez-Ràfols, Dominika Kwasna, Linnan Shen, Iona Wallace, Isobel Cole, Lee A. Armstrong, Axel Knebel, Clare Johnson, Virginia De Cesare, Yogesh Kulathu","doi":"10.1038/s41594-024-01354-y","DOIUrl":"10.1038/s41594-024-01354-y","url":null,"abstract":"Branched ubiquitin (Ub) chains constitute a sizable fraction of Ub polymers in human cells. Despite their abundance, our understanding of branched Ub function in cell signaling has been stunted by the absence of accessible methods and tools. Here we identify cellular branched-chain-specific binding proteins and devise approaches to probe K48–K63-branched Ub function. We establish a method to monitor cleavage of linkages within complex Ub chains and unveil ATXN3 and MINDY as debranching enzymes. We engineer a K48–K63 branch-specific nanobody and reveal the molecular basis of its specificity in crystal structures of nanobody-branched Ub chain complexes. Using this nanobody, we detect increased K48–K63-Ub branching following valosin-containing protein (VCP)/p97 inhibition and after DNA damage. Together with our discovery that multiple VCP/p97-associated proteins bind to or debranch K48–K63-linked Ub, these results suggest a function for K48–K63-branched chains in VCP/p97-related processes. Here the authors assemble a toolkit to probe K48–K63-branched ubiquitin chain function. By identifying specific binders and deubiquitinases and engineering a specific nanobody, they reveal the importance of these chains in p97-dependent processes.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 12","pages":"1872-1887"},"PeriodicalIF":12.5,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41594-024-01354-y.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141556737","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Obscure DNA sequences unveil a new cancer target","authors":"Agnel Sfeir","doi":"10.1038/s41594-024-01347-x","DOIUrl":"10.1038/s41594-024-01347-x","url":null,"abstract":"Curiosity-driven and fundamental discovery science must be justified in its importance to human health and translational potential for practical applications and cures. However, many groundbreaking discoveries occur through the freedom to ask fundamental questions — the how and why — without knowing where they lead. Presented here is an example of a clinical target that emerged from a seemingly simple question in chromosome biology.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 9","pages":"1311-1312"},"PeriodicalIF":12.5,"publicationDate":"2024-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141556978","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Structural basis of MALAT1 RNA maturation and mascRNA biogenesis","authors":"Ilias Skeparnias, Charles Bou-Nader, Dimitrios G. Anastasakis, Lixin Fan, Yun-Xing Wang, Markus Hafner, Jinwei Zhang","doi":"10.1038/s41594-024-01340-4","DOIUrl":"10.1038/s41594-024-01340-4","url":null,"abstract":"The metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) long noncoding RNA (lncRNA) has key roles in regulating transcription, splicing, tumorigenesis, etc. Its maturation and stabilization require precise processing by RNase P, which simultaneously initiates the biogenesis of a 3′ cytoplasmic MALAT1-associated small cytoplasmic RNA (mascRNA). mascRNA was proposed to fold into a transfer RNA (tRNA)-like secondary structure but lacks eight conserved linking residues required by the canonical tRNA fold. Here we report crystal structures of human mascRNA before and after processing, which reveal an ultracompact, quasi-tRNA-like structure. Despite lacking all linker residues, mascRNA faithfully recreates the characteristic ‘elbow’ feature of tRNAs to recruit RNase P and ElaC homolog protein 2 (ELAC2) for processing, which exhibit distinct substrate specificities. Rotation and repositioning of the D-stem and anticodon regions preclude mascRNA from aminoacylation, avoiding interference with translation. Therefore, a class of metazoan lncRNA loci uses a previously unrecognized, unusually streamlined quasi-tRNA architecture to recruit select tRNA-processing enzymes while excluding others to drive bespoke RNA biogenesis, processing and maturation. The authors uncover a Père David’s deer-like design for long noncoding RNAs such as metastasis-associated lung adenocarcinoma transcript 1 (MALAT1), which partially mimics the transfer RNA (tRNA) structure to recruit select tRNA processing enzymes for maturation and to create novel regulatory RNAs such as the MALAT1-associated small cytoplasmic RNA.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 11","pages":"1655-1668"},"PeriodicalIF":12.5,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141489614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Cryo-EM structures of γ-TuRC reveal molecular insights into microtubule nucleation","authors":"Léa Mammri, Paul T. Conduit","doi":"10.1038/s41594-024-01345-z","DOIUrl":"10.1038/s41594-024-01345-z","url":null,"abstract":"Microtubules within cells often have 13 protofilaments but are nucleated by multi-protein y-TuRCs complexes that display 14 γ-tubulin molecules. High-resolution cryo-EM structures of γ-TuRCs after nucleation show that these γ-TuRCs ‘close’ during nucleation to display only 13 γ-tubulin molecules for protofilament assembly.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 7","pages":"1004-1006"},"PeriodicalIF":12.5,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141489617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"cBAF generates subnucleosomes that expand OCT4 binding and function beyond DNA motifs at enhancers","authors":"Marina C. Nocente, Anida Mesihovic Karamitsos, Emilie Drouineau, Manon Soleil, Waad Albawardi, Cécile Dulary, Florence Ribierre, Hélène Picaud, Olivier Alibert, Joël Acker, Marie Kervella, Jean-Christophe Aude, Nick Gilbert, Françoise Ochsenbein, Sophie Chantalat, Matthieu Gérard","doi":"10.1038/s41594-024-01344-0","DOIUrl":"10.1038/s41594-024-01344-0","url":null,"abstract":"The canonical BRG/BRM-associated factor (cBAF) complex is essential for chromatin opening at enhancers in mammalian cells. However, the nature of the open chromatin remains unclear. Here, we show that, in addition to producing histone-free DNA, cBAF generates stable hemisome-like subnucleosomal particles containing the four core histones associated with 50–80 bp of DNA. Our genome-wide analysis indicates that cBAF makes these particles by targeting and splitting fragile nucleosomes. In mouse embryonic stem cells, these subnucleosomes become an in vivo binding substrate for the master transcription factor OCT4 independently of the presence of OCT4 DNA motifs. At enhancers, the OCT4–subnucleosome interaction increases OCT4 occupancy and amplifies the genomic interval bound by OCT4 by up to one order of magnitude compared to the region occupied on histone-free DNA. We propose that cBAF-dependent subnucleosomes orchestrate a molecular mechanism that projects OCT4 function in chromatin opening beyond its DNA motifs. Here, the authors show that the canonical BRG/BRM-associated factor (SWI/SNF) chromatin remodeler generates subnucleosomes containing 50–80 bp of DNA associated with the four core histones. These hemisome-like particles interact with OCT4 to expand its binding domain at enhancers.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 11","pages":"1756-1768"},"PeriodicalIF":12.5,"publicationDate":"2024-07-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141489595","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Single-base tiled screen unveils design principles of PspCas13b for potent and off-target-free RNA silencing","authors":"Wenxin Hu, Amit Kumar, Syed Faraz Ahmed, Shijiao Qi, David K. G. Ma, Honglin Chen, Gurjeet J. Singh, Joshua M. L. Casan, Michelle Haber, Ilia Voskoboinik, Matthew R. McKay, Joseph A. Trapani, Paul G. Ekert, Mohamed Fareh","doi":"10.1038/s41594-024-01336-0","DOIUrl":"10.1038/s41594-024-01336-0","url":null,"abstract":"The development of precise RNA-editing tools is essential for the advancement of RNA therapeutics. CRISPR (clustered regularly interspaced short palindromic repeats) PspCas13b is a programmable RNA nuclease predicted to offer superior specificity because of its 30-nucleotide spacer sequence. However, its design principles and its on-target, off-target and collateral activities remain poorly characterized. Here, we present single-base tiled screening and computational analyses that identify key design principles for potent and highly selective RNA recognition and cleavage in human cells. We show that the de novo design of spacers containing guanosine bases at precise positions can greatly enhance the catalytic activity of inefficient CRISPR RNAs (crRNAs). These validated design principles (integrated into an online tool, https://cas13target.azurewebsites.net/ ) can predict highly effective crRNAs with ~90% accuracy. Furthermore, the comprehensive spacer–target mutagenesis revealed that PspCas13b can tolerate only up to four mismatches and requires ~26-nucleotide base pairing with the target to activate its nuclease domains, highlighting its superior specificity compared to other RNA or DNA interference tools. On the basis of this targeting resolution, we predict an extremely low probability of PspCas13b having off-target effects on other cellular transcripts. Proteomic analysis validated this prediction and showed that, unlike other Cas13 orthologs, PspCas13b exhibits potent on-target activity and lacks collateral effects. This study uses single-base tiled screens, bioinformatics, comprehensive mutagenesis and proteomics to provide a high-resolution view of RNA silencing with PspCas13b. It reveals design principles for potent silencing without collateral effects.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 11","pages":"1702-1716"},"PeriodicalIF":12.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41594-024-01336-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141475334","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Early intermediates in bacterial RNA polymerase promoter melting visualized by time-resolved cryo-electron microscopy","authors":"Ruth M. Saecker, Andreas U. Mueller, Brandon Malone, James Chen, William C. Budell, Venkata P. Dandey, Kashyap Maruthi, Joshua H. Mendez, Nina Molina, Edward T. Eng, Laura Y. Yen, Clinton S. Potter, Bridget Carragher, Seth A. Darst","doi":"10.1038/s41594-024-01349-9","DOIUrl":"10.1038/s41594-024-01349-9","url":null,"abstract":"During formation of the transcription-competent open complex (RPo) by bacterial RNA polymerases (RNAPs), transient intermediates pile up before overcoming a rate-limiting step. Structural descriptions of these interconversions in real time are unavailable. To address this gap, here we use time-resolved cryogenic electron microscopy (cryo-EM) to capture four intermediates populated 120 ms or 500 ms after mixing Escherichia coli σ70–RNAP and the λPR promoter. Cryo-EM snapshots revealed that the upstream edge of the transcription bubble unpairs rapidly, followed by stepwise insertion of two conserved nontemplate strand (nt-strand) bases into RNAP pockets. As the nt-strand ‘read-out’ extends, the RNAP clamp closes, expelling an inhibitory σ70 domain from the active-site cleft. The template strand is fully unpaired by 120 ms but remains dynamic, indicating that yet unknown conformational changes complete RPo formation in subsequent steps. Given that these events likely describe DNA opening at many bacterial promoters, this study provides insights into how DNA sequence regulates steps of RPo formation. Time-resolved cryo-EM captured transient intermediates during E. coli RNAP promoter melting, revealing conformational changes affecting stepwise transcription bubble opening. Results inform how DNA sequence controls bacterial transcription initiation.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 11","pages":"1778-1788"},"PeriodicalIF":12.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141475119","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Asymmetric apical domain states of mitochondrial Hsp60 coordinate substrate engagement and chaperonin assembly","authors":"Julian R. Braxton, Hao Shao, Eric Tse, Jason E. Gestwicki, Daniel R. Southworth","doi":"10.1038/s41594-024-01352-0","DOIUrl":"10.1038/s41594-024-01352-0","url":null,"abstract":"The mitochondrial chaperonin, mitochondrial heat shock protein 60 (mtHsp60), promotes the folding of newly imported and transiently misfolded proteins in the mitochondrial matrix, assisted by its co-chaperone mtHsp10. Despite its essential role in mitochondrial proteostasis, structural insights into how this chaperonin progresses through its ATP-dependent client folding cycle are not clear. Here, we determined cryo-EM structures of a hyperstable disease-associated human mtHsp60 mutant, V72I. Client density is identified in three distinct states, revealing interactions with the mtHsp60 apical domains and C termini that coordinate client positioning in the folding chamber. We further identify an asymmetric arrangement of the apical domains in the ATP state, in which an alternating up/down configuration positions interaction surfaces for simultaneous recruitment of mtHsp10 and client retention. Client is then fully encapsulated in mtHsp60–10, revealing prominent contacts at two discrete sites that potentially support maturation. These results identify distinct roles for the apical domains in coordinating client capture and progression through the chaperone cycle, supporting a conserved mechanism of group I chaperonin function. Cryo-EM structures of the human mitochondrial chaperone Hsp60 reveal alternating apical domain conformations that enable simultaneous client and co-chaperone interactions. These results provide a structural mechanism for efficient client capture and chaperone cycling.","PeriodicalId":49141,"journal":{"name":"Nature Structural & Molecular Biology","volume":"31 12","pages":"1848-1858"},"PeriodicalIF":12.5,"publicationDate":"2024-07-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.nature.com/articles/s41594-024-01352-0.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141475327","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":1,"RegionCategory":"生物学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}