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 coil that speci fically interact with matrix proteins such as fibronectin and laminin. Similar structures are also expressed by Salmonella enteritidis and h ave been denoted thin aggregative fimbriae. Bacteria expressing curli and thin aggregative fimbriae were found to bind radiolabelled plasmin ogen as well as the tissue-type plasminogen activator (t-PA). By contr ast, E. coil carrying a gene locus with an insertionally inactivated c hromosomal curlin subunit were unable to bind the two human proteins. The purified subunit polypeptides of curli and thin aggregative fimbri ae bound plasminogen and t-PA with high affinity (1 x 10(8) to 2 x 10( 8) M(-1)). The binding of plasminogen and t-PA to curli-expressing E. coil was only partially inhibited by fibronectin and laminin. Plasmino gen absorbed from human plasma by curli-expressing E. coil 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 fibrinol ytic proteins and matrix proteins to fimbriae of E. coil and S. enteri tidis could provide these pathogens with both adhesive and invasive pr operties.