Open AccessAlternative σI/anti-σI factors represent a unique form of bacterial σ/anti-σ complex
Author(s) -
Zhen Wei,
Chao Chen,
Yajun Liu,
Sheng Dong,
Jie Li,
Kuan Qi,
Shiyue Liu,
Xiaoke Ding,
Lizett Ortiz de Ora,
Iván Muñoz-Gutiérrez,
Yifei Li,
Hongwei Yao,
Raphael Lamed,
Edward A. Bayer,
Qiu Cui,
Yingang Feng
Publication year - 2019
Publication title -
nucleic acids research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 9.008
H-Index - 537
eISSN - 1362-4954
pISSN - 0305-1048
DOI - 10.1093/nar/gkz355
Subject(s) - biology , cellulosome , clostridium thermocellum , clostridia , homology (biology) , genetics , computational biology , protein structure , biochemistry , bacteria , gene , enzyme , cellulase
The σ70 family alternative σI factors and their cognate anti-σI factors are widespread in Clostridia and Bacilli and play a role in heat stress response, virulence, and polysaccharide sensing. Multiple σI/anti-σI factors exist in some lignocellulolytic clostridial species, specifically for regulation of components of a multienzyme complex, termed the cellulosome. The σI and anti-σI factors are unique, because the C-terminal domain of σI (SigIC) and the N-terminal inhibitory domain of anti-σI (RsgIN) lack homology to known proteins. Here, we report structure and interaction studies of a pair of σI and anti-σI factors, SigI1 and RsgI1, from the cellulosome-producing bacterium, Clostridium thermocellum. In contrast to other known anti-σ factors that have N-terminal helical structures, RsgIN has a β-barrel structure. Unlike other anti-σ factors that bind both σ2 and σ4 domains of the σ 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 σI/anti-σI pairs. We suggest that the σI/anti-σI factors represent a distinctive mode of σ/anti-σ complex formation, which provides the structural basis for understanding the molecular mechanism of the intricate σI/anti-σI system.