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Category: Clinical Microbiology
Molecular Basis of Adherence of Staphylococcus aureus to Biomaterials, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555818067/9781555811778_Chap02-1.gif /docserver/preview/fulltext/10.1128/9781555818067/9781555811778_Chap02-2.gifAbstract:
This chapter focuses on the fibronectin-binding proteins (FnBPs) and fibrinogen-binding proteins (clumping factors, Clf) of Staphylococcus aureus. The role of the proteins in promoting bacterial adherence to immobilized ligand has been defined using site-specific adhesin-defective mutants that are compared with the parental strains in in vitro and in vivo models of foreign-body infection. The fnbA and fnbB genes of the laboratory strain 8325-4 have been inactivated by allelic replacement. This fnbAfhbB double mutant and the mutant carrying a multicopy plasmid that causes overexpression of FnBPA have allowed the role of FnBPs in promoting bacterial interactions with fibronectin to be defined. The fnbAfnbB mutant of strain 8325-4 was also defective in adherence to coverslips removed from subcutaneous chambers implanted in guinea pigs. The growth conditions used to prepare the bacterial cells for the adherence and virulence experiments would have prevented expression of the second clumping factor ClfB. The ClfA- mutant was defective in adherence to immobilized fibrinogen, while the complemented mutant adhered as well as the wild-type. The increasing incidence of multiple-antibiotic-resistant strains causing nosocomial infections has increased the urgency for alternative approaches to prevention and therapy. The problem is compounded by the recent emergence of methicillin-resistant S. aureus (MRSA) with intermediate sensitivity to vancomycin. In conclusion, there are several experimental vaccines that provide clear protection against S. aureus infections in animals. The challenge is to determine if any of these will protect human patients against nosocomial disease and, in particular, biomaterial-related infection.
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Organization of surface proteins of S. aureus. The domain organization of the fibronectin-binding protein A (FnbA), the collagen-binding protein (Cna), fibrinogen-binding protein (ClfA), and protein A (Spa). The signal sequences (S) are removed during secretion across the cytoplasmic membrane. Each protein has common features at the C terminus indicated by the cross-hatched box (LPXTG motif, hydrophobic region, and positively charged residues). Regions W and R are peptidoglycan spanning regions.* indicates position of ligand-binding domains.
Organization of surface proteins of S. aureus. The domain organization of the fibronectin-binding protein A (FnbA), the collagen-binding protein (Cna), fibrinogen-binding protein (ClfA), and protein A (Spa). The signal sequences (S) are removed during secretion across the cytoplasmic membrane. Each protein has common features at the C terminus indicated by the cross-hatched box (LPXTG motif, hydrophobic region, and positively charged residues). Regions W and R are peptidoglycan spanning regions.* indicates position of ligand-binding domains.
Organization of the Clf family of surface proteins. The domain organization of the fibrinogen-binding proteins Clf A and ClfB. The proteins have a repeated region R composed mainly of Ser-Asp dipeptides. S, signal sequence; M, membrane anchor domain including LPXTG motif, hydrophobic residues, and positively charged residues at the C terminus. Within the ligand-binding A regions is the TYTFTDYVD motif (thick broken line) and the DXSXS (MIDAS) motif (thin broken line). The thick continuous line represents an EF-hand loop that is present in region A of ClfA.
Organization of the Clf family of surface proteins. The domain organization of the fibrinogen-binding proteins Clf A and ClfB. The proteins have a repeated region R composed mainly of Ser-Asp dipeptides. S, signal sequence; M, membrane anchor domain including LPXTG motif, hydrophobic residues, and positively charged residues at the C terminus. Within the ligand-binding A regions is the TYTFTDYVD motif (thick broken line) and the DXSXS (MIDAS) motif (thin broken line). The thick continuous line represents an EF-hand loop that is present in region A of ClfA.
Interaction of the ligand-binding region of fibronectin-binding proteins with fibronectin. The wavy line represents the ligand-binding D1-D2-D3 repeats of FnBPs, which do not have secondary structure. The protein interacts with the type I modules of fibronectin and takes on discernable secondary structure with the formation of neoepitopes (ligand-induced binding-site epitopes).
Interaction of the ligand-binding region of fibronectin-binding proteins with fibronectin. The wavy line represents the ligand-binding D1-D2-D3 repeats of FnBPs, which do not have secondary structure. The protein interacts with the type I modules of fibronectin and takes on discernable secondary structure with the formation of neoepitopes (ligand-induced binding-site epitopes).
Structure of fibrinogen. Schematic diagram showing the structural organization of fibrinogen. The globular D domains comprise the C-terminal residues of the α-, β-, and γ-chains. The C terminus of the γ-chain protrudes from the globular γ-module. Binding sites for ClfA and integrins are shown. The E domain contains the N-terminal residues of the α-, β-, and γ-chains cross-linked by disulfide bonds.
Structure of fibrinogen. Schematic diagram showing the structural organization of fibrinogen. The globular D domains comprise the C-terminal residues of the α-, β-, and γ-chains. The C terminus of the γ-chain protrudes from the globular γ-module. Binding sites for ClfA and integrins are shown. The E domain contains the N-terminal residues of the α-, β-, and γ-chains cross-linked by disulfide bonds.