title: Identification and characterization of a novel secreted immunoglobulin binding protein from group A streptococcus.
abstract: Immunoglobulin binding proteins are one of several pathogenicity factors which have been associated with invasive disease caused by group A streptococci. The surface-bound M and M-like proteins of Streptococcus pyogenes are the most characterized of these immunoglobulin binding proteins, and in most cases they bind only a single antibody class. Here we report the identification of a novel non-M-type secreted protein, designated SibA (for secreted immunoglobulin binding protein from group A streptococcus), which binds all immunoglobulin G (IgG) subclasses, the Fc and Fab fragments, and also IgA and IgM. SibA has no significant sequence homology to any M-related proteins, is not found in the vir regulon, and contains none of the characteristic M-protein regions, such as the A or C repeats. Like M proteins, however, SibA does have relatively high levels of alanine, lysine, glutamic acid, leucine, and glycine. SibA and M proteins also share an alpha-helical N-terminal secondary structure which has been previously implicated in immunoglobulin binding in M proteins. Evidence presented here indicates that this is also the case for SibA. SibA also has regions of local similarity with other coiled-coil proteins such as Listeria monocytogenes P45 autolysin, human myosin heavy chain, macrogolgin, and Schistoma mansoni paramyosin, some of which are of potential significance since cross-reactive antibodies between myosin proteins and M proteins have been implicated in the development of the autoimmune sequelae of streptococcal disease.
authors.affiliation: Division of Microbiology, GBF-National Research Center for Biotechnology, Braunschweig, Germany.
authors.forename: P K
authors.initials: PK
authors.lastname: Fagan
authors.forename: D
authors.initials: D
authors.lastname: Reinscheid
authors.forename: B
authors.initials: B
authors.lastname: Gottschalk
authors.forename: G S
authors.initials: GS
authors.lastname: Chhatwal
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics* / Q000276:immunology; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics* / Q000276:immunology; D004269:DNA, Bacterial; D006801:Humans; D007070:Immunoglobulin A / Q000276:immunology; D007074:Immunoglobulin G / Q000276:immunology; D007075:Immunoglobulin M / Q000276:immunology; D007136:Immunoglobulins / Q000378:metabolism; D008969:Molecular Sequence Data; D017422:Sequence Analysis, DNA; D013290:Streptococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D013297:Streptococcus pyogenes / Q000235:genetics* / Q000276:immunology
chemical_list: D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D007070:Immunoglobulin A; D007074:Immunoglobulin G; D007075:Immunoglobulin M; D007136:Immunoglobulins; C433208:SibA protein, Streptococcus pyogenes