title: Evidence for the "dock, lock, and latch" ligand binding mechanism of the staphylococcal microbial surface component recognizing adhesive matrix molecules (MSCRAMM) SdrG.
abstract: Staphylococcus epidermidis is an opportunistic pathogen and a major cause of foreign body infections. The S. epidermidis fibrinogen (Fg)-binding adhesin SdrG is necessary and sufficient for the attachment of this pathogen to Fg-coated materials. Based largely on structural analyses of the ligand binding domain of SdrG as an apo-protein and in complex with a Fg-like peptide, we proposed that SdrG follows a "dock, lock, and latch" mechanism to bind to Fg. This binding mechanism involves the docking of the ligand in a pocket formed between two SdrG subdomains followed by the movement of a C-terminal extension of one subdomain to cover the ligand and to insert and complement a beta-sheet in a neighboring subdomain. These proposed events result in a greatly stabilized closed conformation of the MSCRAMM-ligand complex. In this report, we describe a biochemical analysis of the proposed conformational changes that SdrG undergoes upon binding to its ligand. We have introduced disulfide bonds into SdrG to stabilize the open and closed forms of the apo-form of the MSCRAMM. We show that the stabilized closed form does not bind to the ligand and that binding can be restored in the presence of reducing agents such as dithiothreitol. We have also used Förster resonance energy transfer to dynamically show the conformational changes of SdrG upon binding to its ligand. Finally, we have used isothermic calorimetry to determine that hydrophobic interactions between the ligand and the protein are responsible for re-directing the C-terminal extension of the second subdomain required for triggering the beta-strand complementation event.
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030. Electronic address: gbowden@ibt.tamhsc.edu.
authors.forename: M Gabriela
authors.initials: MG
authors.lastname: Bowden
authors.affiliation: Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, Massachusetts 01003; Department of Molecular and Cellular Medicine, School of Medicine, Texas A&M University System Health Science Center, College Station, Texas 77843.
authors.forename: Alejandro P
authors.initials: AP
authors.lastname: Heuck
authors.affiliation: Center for Biophysical Sciences and Engineering, University of Alabama, Birmingham, Alabama 35294; Center of Advanced Study in Crystallography and Biophysics, University of Madras, Chennai 600025, India.
authors.forename: Karthe
authors.initials: K
authors.lastname: Ponnuraj
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030.
authors.forename: Elena
authors.initials: E
authors.lastname: Kolosova
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030.
authors.forename: Damon
authors.initials: D
authors.lastname: Choe
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030.
authors.forename: Sivashankarappa
authors.initials: S
authors.lastname: Gurusiddappa
authors.affiliation: Center for Biophysical Sciences and Engineering, University of Alabama, Birmingham, Alabama 35294.
authors.forename: Sthanam V L
authors.initials: SVL
authors.lastname: Narayana
authors.affiliation: Department of Molecular and Cellular Medicine, School of Medicine, Texas A&M University System Health Science Center, College Station, Texas 77843.
authors.forename: Arthur E
authors.initials: AE
authors.lastname: Johnson
authors.affiliation: Center for Extracellular Matrix Biology, Institute of Biosciences and Technology, Texas A&M University System Health Science Center, Houston, Texas 77030.
authors.forename: Magnus
authors.initials: M
authors.lastname: Höök
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D005340:Fibrinogen / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D008024:Ligands; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D013050:Spectrometry, Fluorescence; D013212:Staphylococcus epidermidis / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; C112556:Fbe protein, bacteria; D008024:Ligands; D010455:Peptides; D005340:Fibrinogen