SepA, the 110 kDa protein secreted by Shigella flexneri: two-domain structure and proteolytic activity

Abstract

Shigellosis is characterized by a strong inflammatory response which is induced by bacteria invading the colonic mucosa. Characterization of a sepA mutant indicated that SepA, the major protein secreted by Shigeh flexneri growing in laboratory media, might be involved in invasion and destruction of the host intestinal epithelium. The sequence of the first 500 residues of mature SepA (110 kDa) is homologous to that of the N-terminal region of l g A l proteases. To investigate the potential proteolytic activity of SepA, the activity of the purified protein on a wide range of synthetic peptides was tested. SepA hydrolysed several of these substrates and the activity was inhibited by PMSF. Several peptides which were hydrolysed by SepA have been described as specific substrates for cathepsin G, a serine protease produced by polymorphonuclear leukocytes that was proposed to play a role in inflammation. However, unlike cathepsin G, SepA degraded neither fibronectin nor angiotensin I and had no effect on aggregation of human platelets. In addition, analysis of SepA hydrolysis by proteinase K suggested that the protein is composed of two domains of about 450 residues separated by a hinge region of 100 residues. The 47 kDa N-terminal domain was stable and endowed with proteolytic activity.

Comparison of Two Major Forms of the Shigella Virulence Plasmid pINV: Positive Selection Is a Major Force Driving the Divergence

“…It is also possible that the many serotypes are adapted to different variants of the general niche occupied, and that the selection relates to competition between different Shigella clones which differ in details of their adaptation to the niche. The observation that senA (29), a toxin gene apparently under selection pressure for change, and sepA, known to play a role in virulence in S. flexneri serotype 2a (3,4), are absent in some Shigella strains supports the hypothesis that Shigella strains differ in the details of their adaptation to their mode of pathogenesis. A similar explanation may account for the observation that genes under selection pressure differ between E. coli and S. enterica.…”

A Novel Pathogenicity Island Integrated Adjacent to the thrW tRNA Gene of Avian Pathogenic Escherichia coli Encodes a Vacuolating Autotransporter Toxin

“…It has been shown that the serine protease motif is important for phenotypic functions such as cytotoxic and proteolytic activities (20). Some authors predict that casein hydrolytic activity is dependent on the conserved serine protease active-site motif (2,3). The difference in this motif may be the reason that Vat was negative in tests for proteolytic activity on casein-based substrate (data not shown).…”

Type V Protein Secretion Pathway: the Autotransporter Story

“…In 1995, Benjelloun-Touimi et al described a Tsh homologue designated SepA (for Shigella extracellular protein), which is the major extracellular protein of S. flexneri (22). Investigation of the proteolytic activity of SepA utilizing a wide range of synthetic peptides found that SepA hydrolyzed several of these substrates and that the activity was inhibited by the serine protease inhibitor phenylmethylsulfonyl fluoride (PMSF) (23). Several SepA-hydrolyzed peptides were described as specific substrates for cathepsin G, a serine protease produced by polymorphonuclear leukocytes that was proposed to play a role in inflammation.…”