This family consists of the Shigella flexneri specific protein OspC. The function of this family is unknown but it is thought that Osp proteins may be involved in post invasion events related to virulence. Since bacterial pathogens adapt to multiple environments during the course of infecting a host, it has been proposed that Shigella evolved a mechanism to take advantage of a unique intracellular cue, which is mediated through MxiE, to express proteins when the organism reaches the eukaryotic cytosol [1].

1: MxiE regulates intracellular expression of factors secreted by the Shigella flexneri 2a type III secretion system. Kane CD, Schuch R, Day WA Jr, Maurelli AT; J Bacteriol 2002;184:4409-4419. PMID:12142411