CHARACTERIZATION OF ESPC, A 110-KILODALTON PROTEIN SECRETED BY ENTEROPATHOGENIC ESCHERICHIA-COLI WHICH IS HOMOLOGOUS TO MEMBERS OF THE IMMUNOGLOBULIN-A PROTEASE-LIKE FAMILY OF SECRETED PROTEINS

Enteropathogenic Escherichia coli (EPEC) secretes at least five protei ns, Two of these proteins, EspA and EspB (previously called EaeB), act ivate signal transduction pathways in host epithelial cells. While the role of the other three proteins (39, 40, and 110 kDa) remains undete rmined, secretion of all five proteins is under the control of pcrA, a known positive regulator of several EPEC, virulence factors, On the b asis of amino-terminal protein sequence data, se cloned and sequenced the gene which encodes the 110-kDa secreted protein and examined its p ossible role in EPEC signaling and interaction with epithelial cells, In accordance with the terminology used for cspA, and espB, H-e called this gene espC, for EPEC-secreted protein C, We found significant hom ology between the predicted EspC protein sequence and a family of immu noglobulin A (IgA) protease-like proteins which are widespread among p athogenic bacteria, Members of this protein family are found in avian pathogenic Escherichia coli (Tsh), Haemophilus influenzae (Hap), and S higella flexneri (SepA). Although these proteins and EspC do not encod e IgA protease activity, they have considerable homology with IgA prot ease from Neisseria gonorrhoeae and H. influenzae and appear to use a export system for secretion, We found that genes homologous to espC al so exist in other pathogenic bacteria which cause attaching and effaci ng lesions, including Hafnia alvei biotype 19982, Citrobacter freundii biotype 4280, and rabbit diarrheagenic E. coil (RDEC-1). Although the se strains secrete various proteins similar in molecular size to the p roteins secreted by EPEC, se did not detect secretion of a 110-kDa pro tein by these strains, To examine the possible role of EspC in EPEC in teractions with epithelial cells, we constructed a deletion mutant in espC by allelic exchange and characterized the mutant by standard tiss ue culture assays, We found that EspC is hot necessary for mediating E PEC-induced signal transduction in HeLa epithelial cells and does not play a role in adherence or invasion of tissue culture cells.