The outer membrane protein DsrA is the major fibronectin-binding determinant of Haemophilus ducreyi

Departments of Medicine, Microbiology and Immunology, School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC, 27599; Departments of Microbiology and Immunology, Medicine, Pathology and Laboratory Medicine, Indiana University, Indianapolis, IN, 46202

^* To whom correspondence should be addressed. Email: chriselk{at}med.unc.edu.

	Abstract

The ability to bind extracellular matrix proteins is a critical virulence determinant for skin pathogens. Haemophilus ducreyi, the etiological agent of the genital ulcer disease chancroid, binds extracellular matrix components, including fibronectin (FN). We investigated H. ducreyi FN binding and report several important findings about this interaction. First, FN binding by H. ducreyi was greatly increased in bacteria grown on heme and almost completely inhibited by hemoglobin. Second, wild-type strain 35000HP bound significantly more FN than a dsrA mutant in two different FN binding assays. Third, expression of dsrA in the dsrA mutant restored FN binding, and conferred the ability to bind FN to a non-FN binding H. influenzae strain. Fourth, an anti-DsrA monoclonal antibody partially blocked FN binding by H. ducreyi. The hemoglobin receptor, the collagen-binding protein, the H. ducreyi lectin, the fine tangle pili, and the outer membrane OmpA2, were not involved in H. ducreyi FN binding since single mutants bound FN as well as the parent strain. However, MOMP may have a minor role in FN binding by H. ducreyi since a double dsrA/momp mutant bound less FN than the single dsrA mutant. Finally, despite major sequence differences, DsrA from both class I and class II H. ducreyi strains mediated FN and vitronectin binding. We conclude that DsrA is the major factor involved in FN binding by both classes of H. ducreyi strains.