Abstract
Shiga toxin-producing Escherichia coli (STEC) causes outbreaks and sporadic cases of gastroenteritis. STEC O157:H7 is the most clinically relevant serotype in the world. The major virulence determinants of STEC O157:H7 are the Shiga toxins and the locus of enterocyte effacement. However, several accessory virulence factors, mainly outer membrane proteins (OMPs) that interact with the host cells may contribute to the virulence of this pathogen. Previously, the elongation factor thermo unstable (EF-Tu), l-asparaginase II and OmpT proteins were identified as antigens in OMP extracts of STEC. The known subcellular location of EF-Tu and l-asparaginase II are the cytoplasm and periplasm, respectively. Therefore, we investigate whether these two proteins may localize on the surface of STEC and, if so, what roles they have at this site. On the other hand, the OmpT protein, a well characterized protease, has been described as participating in the adhesion of extraintestinal pathogenic E. coli strains. Thus, we investigate whether OmpT has this role in STEC. Our results show that the EF-Tu and l-asparaginase II are secreted by O157:H7 and may also localize on the surface of this bacterium. EF-Tu was identified in outer membrane vesicles (OMVs), suggesting it as a possible export mechanism for this protein. Notably, we found that l-asparaginase II secreted by O157:H7 inhibits T-lymphocyte proliferation, but the role of EF-Tu at the surface of this bacterium remains to be elucidated. In the case of OmpT, we show its participation in the adhesion of O157:H7 to human epithelial cells. Thus, this study extends the knowledge of the pathogenic mechanisms of STEC.
Highlights
Moonlighting proteins are a group of proteins that have multiple and non-mutually exclusive functions, which can be performed in different locations within or outside the cell
NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a cytoplasmic protein involved in the glycolysis pathway, is secreted by Shiga toxin-producing Escherichia coli (STEC) O157:H7 to the culture medium, where it may act as an adhesin that binds to fibrinogen and epithelial cells [8]
We investigate possible novel functions and biological roles of the elongation factor thermo unstable (EF-Tu), l-asparaginase II and OmpT proteins that could contribute to the virulence of STEC
Summary
Moonlighting proteins are a group of proteins that have multiple and non-mutually exclusive functions, which can be performed in different locations within or outside the cell. It has been shown that some bacterial moonlighting proteins involved in metabolism or stress response have a virulence-related function, participating in adhesion, invasion, modulation and evasion of host immune responses [3,4,5,6]. NAD-dependent glyceraldehyde-3-phosphate dehydrogenase (GAPDH), a cytoplasmic protein involved in the glycolysis pathway, is secreted by STEC O157:H7 to the culture medium, where it may act as an adhesin that binds to fibrinogen and epithelial cells [8]. Enolase is another moonlighting protein with a possible role in the pathogenesis of STEC [9]
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