title: The Sbi protein is a multifunctional immune evasion factor of Staphylococcus aureus.
abstract: The second immunoglobulin-binding protein (Sbi) of Staphylococcus aureus has two N-terminal domains that bind the Fc region of IgG in a fashion similar to that of protein A and two domains that can bind to the complement protein C3 and promote its futile consumption in the fluid phase. It has been proposed that Sbi helps bacteria to avoid innate immune defenses. By comparing a mutant defective in Sbi with mutants defective in protein A, clumping factor A, iron-regulated surface determinant H, and capsular polysaccharide, it was shown that Sbi is indeed an immune evasion factor that promotes bacterial survival in whole human blood and the avoidance of neutrophil-mediated opsonophagocytosis. Sbi is present in the culture supernatant and is also associated with the cell envelope. S. aureus strains that expressed truncates of Sbi lacking N-terminal domains D1 and D2 (D1D2) or D3 and D4 (D3D4) or a C-terminal truncate that was no longer retained in the cell envelope were analyzed. Both the secreted and envelope-associated forms of Sbi contributed to immune evasion. The IgG-binding domains contributed only when Sbi was attached to the cell, while only the secreted C3-binding domains were biologically active.
authors.affiliation: Microbiology Department, Moyne Institute of Preventive Medicine, Trinity College, Dublin 2, Ireland.
authors.forename: Emma Jane
authors.initials: EJ
authors.lastname: Smith
authors.forename: Livia
authors.initials: L
authors.lastname: Visai
authors.forename: Steven W
authors.initials: SW
authors.lastname: Kerrigan
authors.forename: Pietro
authors.initials: P
authors.lastname: Speziale
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Foster
mesh_terms: D000942:Antigens, Bacterial / Q000235:genetics / Q000276:immunology; D001422:Bacterial Adhesion; D016667:Bacterial Capsules / Q000235:genetics / Q000276:immunology; D001426:Bacterial Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D002478:Cells, Cultured; D003030:Coagulase / Q000235:genetics / Q000276:immunology; D003176:Complement C3 / Q000096:biosynthesis / Q000276:immunology / Q000378:metabolism; D006801:Humans; D007074:Immunoglobulin G / Q000378:metabolism; D009504:Neutrophils / Q000276:immunology*; D010587:Phagocytosis; D011485:Protein Binding / Q000276:immunology; D017434:Protein Structure, Tertiary; D011956:Receptors, Cell Surface / Q000235:genetics / Q000276:immunology; D013203:Staphylococcal Infections / Q000276:immunology; D013205:Staphylococcal Protein A / Q000235:genetics / Q000276:immunology; D013211:Staphylococcus aureus / Q000235:genetics / Q000276:immunology* / Q000378:metabolism / Q000472:pathogenicity*
chemical_list: D000942:Antigens, Bacterial; D001426:Bacterial Proteins; D002352:Carrier Proteins; C515944:ClfA protein, Staphylococcus aureus; D003030:Coagulase; D003176:Complement C3; D007074:Immunoglobulin G; C512792:IsdH protein, Staphylococcus aureus; D011956:Receptors, Cell Surface; C112405:Sbi protein, Staphylococcus aureus; D013205:Staphylococcal Protein A