title: Two major classes in the M protein family in group A streptococci.
abstract: The M protein family of molecules in the group A streptococcus comprises a number of cell surface proteins that interact with the immune system of the host. One of the proteins in this family is the IgA receptor Arp4, which has C repeats similar to those that characterize the known M proteins. The streptococcal strain expressing Arp4 also expresses a second immunoglobulin-binding protein, Mrp4, which is shown here to be encoded by a gene located immediately upstream of the gene for Arp4. In addition to binding IgG, Mrp4 also binds fibrinogen, a property ascribed to M proteins. DNA sequence analysis demonstrated that the Mrp4 protein indeed is a member of the M protein family, but it was unexpectedly found to have a type of repeat that is identical to the A repeat described for FcRA76, a partially sequenced streptococcal Fc receptor. Purified FcRA76 was shown to bind fibrinogen and IgG, like Mrp4. These data show that the known molecules in the M protein family can be divided into two classes, A and C, according to the type of repeat region found. Hybridization studies with a panel of clinical isolates indicate that many streptococcal strains express class A and class C proteins, whereas some strains express only class C proteins. Class A molecules show amino-terminal sequence variation, like class C molecules, which suggests that proteins of both classes are targets for the immune response.
authors.affiliation: Department of Medical Microbiology, University of Lund, Sweden.
authors.forename: P W
authors.initials: PW
authors.lastname: O'Toole
authors.forename: P
authors.initials: P
authors.lastname: O'Toole
authors.forename: L
authors.initials: L
authors.lastname: Stenberg
authors.forename: M
authors.initials: M
authors.lastname: Rissler
authors.forename: G
authors.initials: G
authors.lastname: Lindahl
mesh_terms: D000595:Amino Acid Sequence; D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins / Q000737:chemistry / Q000145:classification*; D001483:Base Sequence; D002352:Carrier Proteins; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000235:genetics; D005798:Genes, Bacterial; D008969:Molecular Sequence Data; D009838:Oligodeoxyribonucleotides / Q000737:chemistry; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D002352:Carrier Proteins; D004269:DNA, Bacterial; D009838:Oligodeoxyribonucleotides; C014689:streptococcal M protein