title: The Streptococcus gordonii Adhesin CshA Protein Binds Host Fibronectin via a Catch-Clamp Mechanism.
abstract: Adherence of bacteria to biotic or abiotic surfaces is a prerequisite for host colonization and represents an important step in microbial pathogenicity. This attachment is facilitated by bacterial adhesins at the cell surface. Because of their size and often elaborate multidomain architectures, these polypeptides represent challenging targets for detailed structural and functional characterization. The multifunctional fibrillar adhesin CshA, which mediates binding to both host molecules and other microorganisms, is an important determinant of colonization by Streptococcus gordonii, an oral commensal and opportunistic pathogen of animals and humans. CshA binds the high-molecular-weight glycoprotein fibronectin (Fn) via an N-terminal non-repetitive region, and this protein-protein interaction has been proposed to promote S. gordonii colonization at multiple sites within the host. However, the molecular details of how these two proteins interact have yet to be established. Here we present a structural description of the Fn binding N-terminal region of CshA, derived from a combination of X-ray crystallography, small angle X-ray scattering, and complementary biophysical methods. In vitro binding studies support a previously unreported two-state "catch-clamp" mechanism of Fn binding by CshA, in which the disordered N-terminal domain of CshA acts to "catch" Fn, via formation of a rapidly assembled but also readily dissociable pre-complex, enabling its neighboring ligand binding domain to tightly clamp the two polypeptides together. This study presents a new paradigm for target binding by a bacterial adhesin, the identification of which will inform future efforts toward the development of anti-adhesive agents that target S. gordonii and related streptococci.
authors.affiliation: From the School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, United Kingdom.
authors.forename: Catherine R
authors.initials: CR
authors.lastname: Back
authors.affiliation: the Department of Oral Immunology and Infectious Diseases, University of Louisville, Louisville, Kentucky 40202; the Department of Dentistry, University of Information Technology and Management, 35-225 Rzeszow, Poland.
authors.forename: Maryta N
authors.initials: MN
authors.lastname: Sztukowska
authors.affiliation: the School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom; the BrisSynBio Synthetic Biology Research Centre, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom.
authors.forename: Marisa
authors.initials: M
authors.lastname: Till
authors.affiliation: the Department of Oral Immunology and Infectious Diseases, University of Louisville, Louisville, Kentucky 40202.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Lamont
authors.affiliation: From the School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, United Kingdom.
authors.forename: Howard F
authors.initials: HF
authors.lastname: Jenkinson
authors.affiliation: From the School of Oral and Dental Sciences, University of Bristol, Lower Maudlin Street, Bristol BS1 2LY, United Kingdom. Electronic address: Angela.Nobbs@bristol.ac.uk.
authors.forename: Angela H
authors.initials: AH
authors.lastname: Nobbs
authors.affiliation: the School of Biochemistry, University of Bristol, University Walk, Bristol BS8 1TD, United Kingdom; the BrisSynBio Synthetic Biology Research Centre, University of Bristol, Life Sciences Building, Tyndall Avenue, Bristol, BS8 1TQ, United Kingdom. Electronic address: paul.race@bristol.ac.uk.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Race
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018360:Crystallography, X-Ray; D005353:Fibronectins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D000072417:Protein Domains; D054773:Streptococcus gordonii / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D001426:Bacterial Proteins; C079041:CshA protein, Streptococcus gordonii; D005353:Fibronectins; D008565:Membrane Proteins
keywords: X-ray crystallography; adhesin; bacterial pathogenesis; intrinsically disordered protein; microbiology; small-angle X-ray scattering (SAXS)