Subtypes of the plasmid-encoded serine protease EspP in Shiga toxin-producing Escherichia coli: distribution, secretion, and proteolytic activity

Brockmeyer J, Bielaszewska M, Fruth A, Bonn ML, Mellmann A, Humpf HU, Karch H

Abstract

We investigated the prevalence, distribution, and structure of espP in Shiga toxin-producing Escherichia coli (STEC) and assessed the secretion and proteolytic activity of the encoded autotransporter protein EspP (extracellular serine protease, plasmid encoded). espP was identified in 56 of 107 different STEC serotypes. Sequencing of a 3,747-bp region of the 3,900-bp espP gene distinguished four alleles (espP alpha, espP beta, espP gamma, and espP delta, with 99.9%, 99.2%, 95.3%, and 95.1% homology, respectively, to espP of E. coli O157:H7 strain EDL933. The espP beta, espP gamma, and espP delta genes contained unique insertions and/or clustered point mutations that enabled allele-specific PCRs; these demonstrated the presence of espP alpha, espP beta, espP-gamma, and espP delta in STEC isolates belonging to 17, 16, 15, and 8 serotypes, respectively. Among four subtypes of EspP encoded by these alleles, EspP alpha (produced by enterohemorrhagic E. coli [EHEC] O157:H7 and the major non-O157 EHEC serotypes) and EspP gamma cleaved pepsin A, human coagulation factor V, and an oligopeptide alanine-alanine-proline-leucine-para-nitroaniline, whereas EspP beta and EspP delta either were not secreted or were proteolytically inactive. The lack of proteolysis correlated with point mutations near the active serine protease site. We conclude that espP is widely distributed among STEC strains and displays genetic heterogeneity, which can be used for subtyping and which affects EspP activity. The presence of proteolytically active EspP in EHEC serogroups O157, O26, 0111, and 0145, which are bona fide human pathogens, suggests that EspP might play a role as an EHEC virulence factor.