Plasminogen, absorbed by Escherichia coli expressing curli or by Salmonella enteritidis expressing thin aggregative fimbriae, can be activated by simultaneously captured tissue-type plasminogen activator (t-PA)

Curli are fimbrial structures expressed by Escherichia coli that specifically interact with matrix proteins such as fibronectin and laminin. Similar structures are also expressed by Salmonella enteritidis and have been denoted thin aggregative fimbriae. Bacteria expressing curli and thin aggregative fimbriae were found to bind radiolabelled plasminogen as well as the tissue-type plasminogen activator (t-PA). By contrast, E. coli carrying a gene locus with an insertionally inactivated chromosomal curlin subunit were unable to bind the two human proteins. The purified subunit polypeptides of curli and thin aggregative fimbriae bound plasminogen and t-PA with high affinity (1 × 10⁸ to 2 × 10⁸ M^-1). The binding of plasminogen and t-PA to curli-expressing E. coli was only partially inhibited by fibronectin and laminin. Plasminogen absorbed from human plasma by curli-expressing E. coli was readily converted to plasmin by t-PA; both plasmin and t-PA were functionally active when bound to the bacteria. A simultaneous binding of fibrinolytic proteins and matrix proteins to fimbriae of E. coli and S. enteritidis could provide these pathogens with both adhesive and invasive properties.