6ivu
Solution structure of the Sigma-anti-sigma factor complex RsgI1N-SigI1C from Clostridium thermocellum
Structural highlights
FunctionRSGI1_ACET2 Anti-sigma factor for SigI1. Negatively regulates SigI1 activity through direct interaction (PubMed:20937888). Binding of the polysaccharide substrate to the extracellular C-terminal sensing domain of RsgI1 may induce a conformational change in its N-terminal cytoplasmic region, leading to the release and activation of SigI1 (Probable).[1] [2] Publication Abstract from PubMedThe sigma70 family alternative sigmaI factors and their cognate anti-sigmaI factors are widespread in Clostridia and Bacilli and play a role in heat stress response, virulence, and polysaccharide sensing. Multiple sigmaI/anti-sigmaI factors exist in some lignocellulolytic clostridial species, specifically for regulation of components of a multienzyme complex, termed the cellulosome. The sigmaI and anti-sigmaI factors are unique, because the C-terminal domain of sigmaI (SigIC) and the N-terminal inhibitory domain of anti-sigmaI (RsgIN) lack homology to known proteins. Here, we report structure and interaction studies of a pair of sigmaI and anti-sigmaI factors, SigI1 and RsgI1, from the cellulosome-producing bacterium, Clostridium thermocellum. In contrast to other known anti-sigma factors that have N-terminal helical structures, RsgIN has a beta-barrel structure. Unlike other anti-sigma factors that bind both sigma2 and sigma4 domains of the sigma factors, RsgIN binds SigIC specifically. Structural analysis showed that SigIC contains a positively charged surface region that recognizes the promoter -35 region, and the synergistic interactions among multiple interfacial residues result in the specificity displayed by different sigmaI/anti-sigmaI pairs. We suggest that the sigmaI/anti-sigmaI factors represent a distinctive mode of sigma/anti-sigma complex formation, which provides the structural basis for understanding the molecular mechanism of the intricate sigmaI/anti-sigmaI system. Alternative sigmaI/anti-sigmaI factors represent a unique form of bacterial sigma/anti-sigma complex.,Wei Z, Chen C, Liu YJ, Dong S, Li J, Qi K, Liu S, Ding X, Ortiz de Ora L, Munoz-Gutierrez I, Li Y, Yao H, Lamed R, Bayer EA, Cui Q, Feng Y Nucleic Acids Res. 2019 May 20. pii: 5490815. doi: 10.1093/nar/gkz355. PMID:31106374[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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