This family of proteins is found in bacteria and includes YfiR from E. coli. YfiR has been shown to regulate YfiN, a diguanylate cyclase and a bifunctional protein that produces c-di-GMP in response to reductive stress and then dynamically relocates to the division site to arrest cell division in response to envelope stress in Escherichia coli. YfiR may serve as a periplasmic redox sensor that regulates YfiN activity in response to reducing conditions [1, 2]. HmsC in Yersinia Pestis is the orthologue of YfiR from E. coli [3]. HmsC is a periplasmic protein that interacts directly with the periplasmic domain (PD) of HmsD and causes proteolytic degradation of HmsD, which in turn negatively regulates Y. pestis biofilm formation [4].

1: Crystal structures of YfiR from Pseudomonas aeruginosa in two redox states. Yang X, Yang XA, Xu M, Zhou L, Fan Z, Jiang T; Biochem Biophys Res Commun. 2015;461:14-20. PMID:25849887

2: A Diguanylate Cyclase Acts as a Cell Division Inhibitor in a Two-Step Response to Reductive and Envelope Stresses. Kim HK, Harshey RM; MBio. 2016; [Epub ahead of print] PMID:27507823

3: The Yersinia pestis HmsCDE regulatory system is essential for blockage of the oriental rat flea (Xenopsylla cheopis), a classic plague vector. Bobrov AG, Kirillina O, Vadyvaloo V, Koestler BJ, Hinz AK, Mack D, Waters CM, Perry RD; Environ Microbiol. 2015;17:947-959. PMID:25586342

4: HmsC, a periplasmic protein, controls biofilm formation via repression of HmsD, a diguanylate cyclase in Yersinia pestis. Ren GX, Yan HQ, Zhu H, Guo XP, Sun YC; Environ Microbiol. 2014;16:1202-1216. PMID:24192006