title: Curli, fibrous surface proteins of Escherichia coli, interact with major histocompatibility complex class I molecules.
abstract: 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 class II (MHC-II) molecules. Curliated E. coli was found to interact with an MHC-I-expressing lymphoma cell line as shown by scanning electron microscopy, whereas the binding to a mutant variant of this cell line expressing small amounts of MHC-I molecules was significantly lower. Moreover, curli-expressing E. coli bound purified radiolabeled MHC-I but not MHC-II molecules, whereas an isogenic curli-deficient mutant strain showed no affinity for either MHC-I or MHC-II. Purified insoluble curli could also bind 125I-labeled MHC-I molecules, and in Western blot experiments the 15-kDa curlin subunit protein bound intact MHC-I molecules as well as beta2-microglobulin, the light chain of MHC-I molecules. A direct interaction between monomeric MHC-I molecules and a bacterial surface protein has previously not been reported. The binding of curli to MHC-I molecules, which are present on virtually all cells in higher vertebrates, will provide curliated E. coli with ample opportunities to interact with a great variety of hosts and host cells. This should facilitate the adaptation of E. coli to different ecological niches, and in human infections the interaction between curli and MHC-I molecules could contribute to adherence and colonization.
authors.affiliation: Section for Molecular Pathogenesis, Department of Cell and Molecular Biology, Lund University, Sweden. arne.olsen@medkem.lu.se
authors.forename: A
authors.initials: A
authors.lastname: Olsén
authors.forename: M J
authors.initials: MJ
authors.lastname: Wick
authors.forename: M
authors.initials: M
authors.lastname: Mörgelin
authors.forename: L
authors.initials: L
authors.lastname: Björck
mesh_terms: D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000378:metabolism*; D004926:Escherichia coli / Q000502:physiology*; D029968:Escherichia coli Proteins; D015395:Histocompatibility Antigens Class I / Q000378:metabolism*; D006801:Humans
chemical_list: D001426:Bacterial Proteins; D029968:Escherichia coli Proteins; D015395:Histocompatibility Antigens Class I; C489688:csgA protein, E coli; C077481:Crl protein, Bacteria