title: The ShdA adhesin binds to the cationic cradle of the fibronectin 13FnIII repeat module: evidence for molecular mimicry of heparin binding.
abstract: Introduction of Salmonella enterica serotype Typhimurium into food products results from its ability to persist in the intestine of healthy livestock by mechanisms that are poorly understood. The non-fimbrial adhesin ShdA is a fibronectin binding protein required for persistent intestinal carriage of S. Typhimurium. We further investigated the molecular mechanism of ShdA-mediated intestinal persistence by determining the binding-site of this receptor in fibronectin. Analysis of ShdA binding to fibronectin proteolytic fragments and to recombinant fibronectin fusion proteins identified the (13)FnIII repeat module of the Hep-2 domain as the primary binding site for this adhesin. The (13)FnIII repeat module of fibronectin contains a cationic cradle formed by six basic residues (R6, R7, R9, R23, K25 and R54) that is a high affinity heparin-binding site conserved among fibronectin sequences from frogs to man. Binding of ShdA to the (13)FnIII repeat module of fibronectin and to a second extracellular matrix protein, Collagen I, could be inhibited by heparin. Furthermore, binding of ShdA to the Hep-2 domain was sensitive to the ionic buffer strength, suggesting that binding involved ionic interactions. We therefore determined whether amino acid substitutions of basic residues in the cationic cradle of the Hep-2 domain that inhibit heparin binding also abrogate binding of ShdA. Combined substitution of R6S and R7S strongly reduced ShdA binding to (13)FnIII. These data suggest that ShdA binds the Hep-2 domain of fibronectin by a mechanism that may mimic binding of the host polysaccharide heparin.
authors.affiliation: Department of Medical Microbiology and Immunology, College of Medicine, Texas A and M University System Health Science Center, 407 Reynolds Medical Building, College Station, TX77843-1114, USA. rkingsleyu@medicine.tamu.edu
authors.forename: Robert A
authors.initials: RA
authors.lastname: Kingsley
authors.forename: A Marijke
authors.initials: AM
authors.lastname: Keestra
authors.forename: Marcel R
authors.initials: MR
authors.lastname: de Zoete
authors.forename: Andreas J
authors.initials: AJ
authors.lastname: Bäumler
mesh_terms: D000818:Animals; D000990:Antithrombin III / Q000378:metabolism; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites; D002412:Cations; D003094:Collagen / Q000378:metabolism; D005353:Fibronectins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006493:Heparin / Q000378:metabolism*; D006801:Humans; D008958:Models, Molecular; D018716:Molecular Mimicry; D016297:Mutagenesis, Site-Directed; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000378:metabolism; D012486:Salmonella typhimurium / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D001425:Bacterial Outer Membrane Proteins; D002412:Cations; D005353:Fibronectins; D010446:Peptide Fragments; D011994:Recombinant Proteins; C409034:ShdA protein, Salmonella enterica; D000990:Antithrombin III; D006493:Heparin; D003094:Collagen