Abstract
Dispersin is a 10.2 kDa-immunogenic protein secreted by enteroaggregative Escherichia coli (EAEC). In the prototypical EAEC strain 042, dispersin is non-covalently bound to the outer membrane, assisting dispersion across the intestinal mucosa by overcoming electrostatic attraction between the AAF/II fimbriae and the bacterial surface. Also, dispersin facilitates penetration of the intestinal mucus layer. Initially characterized in EAEC, dispersin has been detected in other E. coli pathotypes, including those isolated from extraintestinal sites. In this study we investigated the binding capacity of purified dispersin to extracellular matrix (ECM), since dispersin is exposed on the bacterial surface and is involved in intestinal colonization. Binding to plasminogen was also investigated due to the presence of conserved carboxy-terminal lysine residues in dispersin sequences, which are involved in plasminogen binding in several bacterial proteins. Moreover, some E. coli components can interact with this host protease, as well as with tissue plasminogen activator, leading to plasmin production. Recombinant dispersin was produced and used in binding assays with ECM molecules and coagulation cascade compounds. Purified dispersin bound specifically to laminin and plasminogen. Interaction with plasminogen occurred in a dose-dependent and saturable manner. In the presence of plasminogen activator, bound plasminogen was converted into plasmin, its active form, leading to fibrinogen and vitronectin cleavage. A collection of E. coli strains isolated from human bacteremia was screened for the presence of aap, the dispersin-encoding gene. Eight aap-positive strains were detected and dispersin production could be observed in four of them. Our data describe new attributes for dispersin and points out to possible roles in mechanisms of tissue adhesion and dissemination, considering the binding capacity to laminin, and the generation of dispersin-bound plasmin(ogen), which may facilitate E. coli spread from the colonization site to other tissues and organs. The cleavage of fibrinogen in the bloodstream, may also contribute to the pathogenesis of sepsis caused by dispersin-producing E. coli.
Highlights
Dispersin is a 10.2-kDa positively charged surface protein, which was initially characterized in enteroaggregative Escherichia coli (EAEC) prototypical strain 042 (Sheikh et al, 2002)
We showed that dispersin can bind to laminin and plasminogen, and dispersin-bound plasminogen is converted into active plasmin in the presence of uPa, which in turn cleaves vitronectin and fibrinogen
As AafA and dispersin are exposed on the bacterial surface, our data suggest that laminin binding could be a combined feature of both proteins, at least in strains expressing aggregative adherence fimbriae II (AAF/II) and dispersin
Summary
Dispersin is a 10.2-kDa positively charged surface protein, which was initially characterized in enteroaggregative Escherichia coli (EAEC) prototypical strain 042 (Sheikh et al, 2002). This protein is encoded by the aap (antiaggregation protein) gene and is secreted across the bacterial cell membrane by the enteroaggregative ABC transporter (Aat) system, remaining non-covalently attached to the bacterial surface (Nishi et al, 2003). In EAEC 042 dispersin neutralizes the bacterial cell surface by repelling and projecting the positively charged aggregative adherence fimbriae II (AAF/II), leading to anti-aggregation and dispersal of bacteria on the intestinal mucosa (Velarde et al, 2007). The presence of aap was detected in EAEC strains capable to cause urinary tract infection (Olesen et al, 2012; Boll et al, 2013; Herzog et al, 2014) and in Shiga toxin-producing EAEC of serotypes O104:H4 and 0111:H21 (Scheutz et al, 2011; Dallman et al, 2012)
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