Characterization of an exported protease from Shiga toxin‐producing Escherichia coli

Abstract

SummaryThe gene for a novel, high molecular weight protein secreted by Shiga toxin-producing Escherichia coli (STEC) has been cloned, sequenced and characterized with respect to its activity. This gene, designated pssA, is localized on the large plasmid that also harbours the STEC haemolysin operon. Sequencing of a region comprising 10 630 nt revealed that the sequences flanking the pssA gene are composed of several remnants of different insertion elements. The PssA protein is produced as a 142 kDa precursor molecule that, after N-and C-terminal processing, is released into the culture supernatant as a mature polypeptide of approximately 104 kDa. The primary sequence of PssA is highly related to a family of autonomously transported putative virulence factors from different Gram-negative pathogens, which includes the Tsh protein of an avian-pathogenic E. coli strain, the SepA protein from Shigella flexneri and the EspC protein from enteropathogenic E. coli. A common motif present in all four proteins is reminiscent of the catalytic centre of certain serine proteases. PssA (protease secreted by STEC) indeed shows serine protease activity in a casein-based assay and is moreover cytotoxic for Vero cells. This activity of PssA and probably of other proteins of the Tsh family may be of functional importance during infection of the mucosal cell layer by the bacterial pathogen.

VTEC enteropathogenicity

“…At the same time, Djafari et al (1997) described a protease d ' ' terme protease secreted by STEC' A or PssA, which appears to be the same as that reported by Brunder et al (1997). This protease was encoded on the espP gene located on the large plasmid carried by 0157 VTEC and was a 104 kDa protein.…”

Bacterial Macroscopic Rope-like Fibers with Cytopathic and Adhesive Properties

“…EspP (also known as PssA) is considered by some authors to be a cytotoxin because it causes cytotoxic effects on Vero cells (38). We found that incubation of HeLa cell monolayers with bacteria-free ropes or EspP monomers for 24 h led to cell rounding (Fig.…”

“…People naturally or experimentally infected with EPEC or EHEC develop antibodies against EspC or EspP, respectively (38,43). We found that a pool of sera obtained from HUS patients reacted with the rope-forming EspP protein, whereas normal human sera did not show any reactivity.…”

Type V Protein Secretion Pathway: the Autotransporter Story

“…In 1997, almost simultaneously Brunder et al (49) described EspP (for "extracellular serine protease plasmid-encoded") and Djafari et al (106) described PssA (for "protease secreted by STEC") in EHEC O157:H7 and Shiga-toxin producing E. coli (STEC) O26:HϪ, respectively. These proteins are identical, are encoded on the large virulence plasmids, and represent the major extracellular proteins of both organisms.…”

“…On the other hand, both proteins are highly im- (49,106). Interestingly, different biological activities were described for EspP and PssA.…”