This family consists of a number of bacterial sequences which are highly similar to the Tir chaperone protein in E. Coli. In many Gram-negative bacteria, a key indicator of pathogenic potential is the possession of a specialised type III secretion system, which is utilised to deliver virulence effector proteins directly into the host cell cytosol. Many of the proteins secreted from such systems require small cytosolic chaperones to maintain the secreted substrates in a secretion-competent state. CesT serves a chaperone function for the enteropathogenic Escherichia coli (EPEC) translocated intimin receptor (Tir) protein, which confers upon EPEC the ability to alter host cell morphology following intimate bacterial attachment [1]. This family also contains several DspF and related sequences from several plant pathogenic bacteria. The "disease-specific" (dsp) region next to the hrp gene cluster of Erwinia amylovora is required for pathogenicity but not for elicitation of the hypersensitive reaction. DspF and AvrF are small (16 kDa and 14 kDa) and acidic with predicted amphipathic alpha helices in their C termini; they resemble chaperones for virulence factors secreted by type III secretion systems of animal pathogens [2].

1: Functional analysis of the enteropathogenic Escherichia coli type III secretion system chaperone CesT identifies domains that mediate substrate interactions. Delahay RM, Shaw RK, Elliott SJ, Kaper JB, Knutton S, Frankel G; Mol Microbiol 2002;43:61-73. PMID:11849537

2: Homology and functional similarity of an hrp-linked pathogenicity locus, dspEF, of Erwinia amylovora and the avirulence locus avrE of Pseudomonas syringae pathovar tomato. Bogdanove AJ, Kim JF, Wei Z, Kolchinsky P, Charkowski AO, Conlin AK, Collmer A, Beer SV; Proc Natl Acad Sci U S A 1998;95:1325-1330. PMID:9448330