CURLI, FIBROUS SURFACE-PROTEINS OF ESCHERICHIA-COLI, INTERACT WITH MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I MOLECULES

Curli are thin, coiled fibers expressed on the surface of Escherichia coli that bind several matrix and plasma proteins such as fibronectin, laminin, plasminogen, tissue plasminogen activator, and H-kininogen, In this work, we examined the interactions between curli-expressing E. coli and human major histocompatibility complex class I (MHC-I) and c lass II (MHC-II) molecules. Curliated E. coli was found to interact wi th an MHC-I-expressing lymphoma cell line as shown by scanning electro n microscopy, whereas the binding to a mutant variant of this cell lin e expressing small amounts of MHC-I molecules was significantly lower. Moreover, curli-expressing E. coli bound purified radiolabeled MHC-I bat not MHC-II molecules, whereas an isogenic curli-deficient mutant s train showed no affinity for either MHC-I or MHC-II. Purified insolubl e curli could also bind I-125-labeled MHC-I molecules, and in Western blot experiments the 15-kDa curlin subunit protein bound intact MHC-I molecules as well as beta(2)-microglobulin, the light chain of MHC-I m olecules. ?a direct interaction between monomeric MHC-I molecules and a bacterial surface protein has previously not been reported. The bind ing of curli to MHC-I molecules, which are present on virtually all ce lls in higher vertebrates, will provide curliated E. coli with ample o pportunities to interact with a great variety of hosts and host cells, This should facilitate the adaptation of E. coli to different ecologi cal niches, and in human infections the interaction between curli and MHC-I molecules could contribute to adherence and colonization.