Alternative σi/anti-σI factors represent a unique form of bacterial σ/anti-σ complex

Zhen Wei, Chao Chen, Ya Jun Liu, Sheng Dong, Jie Li, Kuan Qi, Shiyue Liu, Xiaoke Ding, Lizett Ortiz De Ora, Iván Munoz-Gutíerrez, Yifei Li, Hongwei Yao, Raphael Lamed, Edward A. Bayer, Qiu Cui, Yingang Feng

Research output: Contribution to journalArticlepeer-review


The σ 70 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 amongmultiple 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.

Original languageEnglish
Pages (from-to)5988-5997
Number of pages10
JournalNucleic Acids Research
Issue number11
StatePublished - 20 Jun 2019


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