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Alternative ?I/anti-?I factors represent a unique form of bacterial ?/anti-? complex.


ABSTRACT: The ?70 family alternative ?I factors and their cognate anti-?I factors are widespread in Clostridia and Bacilli and play a role in heat stress response, virulence, and polysaccharide sensing. Multiple ?I/anti-?I factors exist in some lignocellulolytic clostridial species, specifically for regulation of components of a multienzyme complex, termed the cellulosome. The ?I and anti-?I factors are unique, because the C-terminal domain of ?I (SigIC) and the N-terminal inhibitory domain of anti-?I (RsgIN) lack homology to known proteins. Here, we report structure and interaction studies of a pair of ?I and anti-?I factors, SigI1 and RsgI1, from the cellulosome-producing bacterium, Clostridium thermocellum. In contrast to other known anti-? factors that have N-terminal helical structures, RsgIN has a ?-barrel structure. Unlike other anti-? factors that bind both ?2 and ?4 domains of the ? 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 ?I/anti-?I pairs. We suggest that the ?I/anti-?I factors represent a distinctive mode of ?/anti-? complex formation, which provides the structural basis for understanding the molecular mechanism of the intricate ?I/anti-?I system.

SUBMITTER: Wei Z 

PROVIDER: S-EPMC6582324 | BioStudies | 2019-01-01

REPOSITORIES: biostudies

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