Epitope structure of fibronectin that recognized by bacterial adhesins

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Fibronectin (Fn) is a major extracellular matrix protein and appears to mediate adherence of various microorganisms to host tissues at the first stage of infections. Granulicatella adiacens, a dominant nutritionally variant streptococci (NVS) harboring in the healthy human oral cavities, is often isolated from patients with infective endocarditis as the causative agent. We have previously reported a link between the Fn-binding ability of this specie and the infectivity in an animal model of endocarditis. We report herein that Fn possesses a novel binding site for various species of bacteria including this organism, and the region may be more relevant to microbial pathogenesis than the N-terminal region which has been extensively investigated from this point of view. Monoclonal antibodies (mAbs) were generated against human Fn, and one clone with an ability to inhibit the Fn-binding of G. adiacens was selected. Western blotting analyses using polypeptide fragments of Fn obtained by sequ … More ential limited digestions with thermolysin and lysyl endopeptidase showed that the epitope for the inhibiting mAb resided in the central part of the whole Fn polypeptide (105 kDa cell-binding fragment) which lacked both the N- and C-terminal parts, the former contains the known binding regions for many bacterial species. Staphylococcus aureus and Streptococcus pyogenes were also capable of binding to the central 105 kDa cell-binding fragment immobilized onto assay plates, in addition to the known binding to the N-terminal part while G. adiacens and an Echerichia coli were only to the central part. The adherence of S. aureus and S. pyogenes to N-terminal Fn fragment was inhibited by excess amounts of free Fn in the assay medium. In contrast, adherence of the four species to the central 105 kDa fragment was not inhibited by soluble Fn, but by the mAb. Considering the high concentrations of soluble Fn in the mammalian body fluids, the central part of Fn may have more important roles than the N-terminal region in the bacterial adherence in vivo. Less