Cellular Traffic Jam and Disease Due to Mutations in SRP54

In this issue of Structure, Juaire et al. use X-ray crystallography, biophysical tools, and cell-based assays to investigate disease-associated variants the SRP54 GTPase demonstrate that defects in SRP-mediated protein secretion can explain phenotypes severe neutropenia with Shwachman-Diamond-syndrome-like symptoms. The advent modern DNA sequencing technology has revolutionized biology medicine, it become feasible, affordable, commonplace correlate biological diagnostic alterations genomic genome-wide association studies (GWASs). But correlation does not imply causation. To gain mechanistic insight establish causal links, GWAS-type experiments need be followed up by quantitative structure-activity relationship (QSAR) analyses molecules question, which frequently are still painstakingly difficult laborious perform. coworkers present a beautiful example such QSAR-type analysis. They effect mutations GTPase, had previously been correlated rare type human genetic disease, an autosomal dominant Shwachman-Diamond syndrome (SDS)-like symptoms (Carapito al., 2017Carapito R. Konantz M. Paillard C. Miao Z. Pichot A. Leduc M.S. Yang Y. Bergstrom K.L. Mahoney D.H. Shardy D.L. al.Mutations signal recognition particle cause syndromic Shwachman-Diamond-like features.J. Clin. Invest. 2017; 127: 4090-4103Crossref PubMed Scopus (66) Google Scholar; Bellanné-Chantelot 2018Bellanné-Chantelot Schmaltz-Panneau B. Marty Fenneteau O. Callebaut I. Clauin S. Docet Damaj G.L. Leblanc T. Pellier gene congenital as well syndrome.Blood. 2018; 132: 1318-1331Crossref (44) Scholar). A is characterized severely reduced number neutrophil granulozytes (or neutrophils), very frequent white blood cell charged phagocytose pathogens part innate immune response. SDS-like additionally include insufficient development from pancreas, neurodevelopmental skeletal disorders. Importantly, many could explained deficiencies co-translational targeting endoplasmic reticulum, affecting both differentiation maturation affected types their precursors final function highly conserved catalytic (SRP). SRP ribonucleoprotein composed structured RNA (7SL RNA) six proteins (SRP9, SRP14, SRP19, SRP54, SRP68, SRP72). It responsible for mRNA-ribosome-nascent chain complexes Sec61 membrane translocation pores at where interacts another, structurally similar SR?. This complex SR? called (TC). Upon GTP hydrolysis, nascent secretory then enters pore translocation, whereas dissociates becomes available another round (Grudnik 2009Grudnik P. Bange G. Sinning Protein particle.Biol. Chem. 2009; 390: 775-782Crossref (114) Akopian 2013Akopian D. Shen K. Zhang X. Shan S.O. Signal particle: essential protein-targeting machine.Annu. Rev. Biochem. 2013; 82: 693-721Crossref (236) consists three domains: N (N-terminal), G (GTP binding), M (methionine rich). M-domain assembles defined orientation participates sequence recognition, N- G-domains (also named NG-domain) remains tethered flexible fashion. all originally identified Carapito subsequently also map G-domain SRP54. Having studied structure mechanism more than two decades, implication disease prompted lab join forces members Bahram corroborate causative nature (T115A, T117del, G226E) obtain observed phenotypes. aim, they combined crystallography complementary biophysical, biochemical, cell-biological analyses. first step, obtained crystal formed between NG-domains presence analog, GMPPNP (Figure 1, PDB: 6Y32). Furthermore, crystals isolated NG-domain (PDB: 6Y2Z) NG T115A 6Y30) T117del 6Y31), G226E variant did crystallize. important addition catalog structures. demonstrates binding formation illustrates relative location investigated G-domain. T115 P loop, characteristic element GTP-binding domains fixes bound analog. lacks one threonines T115-T116-T117 consequences P-loop backbone conformation. contrast, G226 far site, loop contacting N-domain, interface 1). agreement these observations, lost ability bind microscale thermophoresis (MST) experiments, showed increased affinity GTP. MST, monitors diffusion locally induced temperature gradient, particularly sensitive small molecule binding. Nevertheless, failed TC formation. For variants, interaction was tested vitro size exclusion chromatography static light scattering, cells expression homologous yeast context two-hybrid experiment. noticed structures display elevated crystallographic B-factors throughout portions G-domain, hinting widespread destabilization molecules. observation confirmed thermal melting solution using differential scanning fluorimetry (nano-DSF), unfolded lower wild-type NG-domain. however, different T115/T117del respectively. concluded hydrogen-deuterium exchange mass-spectrometry D2O-solvent-exposed protons on surface exchanged rapidly those its core. Such observations important, indicate regionally affect functions eventually correlating strength Finally, living cells. experiment, used deletion strain defect growth supplemented corresponding homologs variants. Only restore normal demonstrating functionally rescue phenotype. second experiment conducted HEK293 cells, or respective were overexpressed, monitoring marker protein. Here, appear have dominant-negative over endogenous copies protein, jamming reporter leading cytosolic mis-targeting and/or degradation mRNPs. summary, provide compelling support impair neutropenias reasonable speculate certain simply haplo-insufficiency, general mRNA translation initiation factor eIF4E cancer (Truitt 2015Truitt M.L. Conn C.S. Shi Pang Tokuyasu Coady A.M. Seo Barna Ruggero Differential Requirements Dose Normal Development Cancer.Cell. 2015; 162: 59-71Abstract Full Text PDF (186) case, processes require high dose cannot provided single remaining functional copy gene. Other may compensated gene, family Ras-like GTPases causing (Liu 2017Liu W.N. Yan Chan thirty-year quest role R-Ras cancer: oncogene multitasking GTPase.Cancer Lett. 403: 59-65Crossref (22) primarily formation, but otherwise assemble normally into via M-domain, depletion components accumulation stalled mistargeted mRNPs cleared cytosol (Pinarbasi 2018Pinarbasi E.S. Karamyshev A.L. Tikhonova E.B. Wu I.H. Hudson H. Thomas P.J. Pathogenic Sequence Mutations Progranulin Disrupt Interactions Required Stability.Cell Rep. 23: 2844-2851Abstract (18) Lakshminarayan 2020Lakshminarayan Phillips B.P. Binnian I.L. Gomez-Navarro N. Escudero-Urquijo Warren A.J. Miller E.A. Pre-emptive Quality Control Misfolded Membrane Ribosome-Driven Effects.Curr. Biol. 2020; 30: 854-864.e5Abstract (16) Clearly, would diverse possibly stronger SDS-type tools described together suitable animal models (zebrafish, mouse, developed) should facilitate analysis classification future These expected patients generated experimentally analogy disease-causing other GTPases, will only further our understanding lead fundamental detailed picture SRP-dependent process. careful point out each mutation distinct multiple effects modulated background. continued progress large-scale data ever fine-tuned according underlying genotype ultimately make possible design personalized therapies based upon particular sets (Ashley, 2016Ashley Towards precision medicine.Nat. Genet. 2016; 17: 507-522Crossref (300) I wish acknowledge individuals who contributed pathway, investigating physiological relevance remain uncited here due space limitations. Structural Functional Impact Causing Severe Congenital NeutropeniaJuaire al.StructureOctober 13, 2020In BriefJuaire linked neutropenia, critically destabilized regions increase overall flexibility. negatively impact receptor, thereby pathway. Full-Text