Two major classes in the M protein family in group A streptococci

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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.",
author = "O'Toole, {Paul W.} and Lars Stenberg and Marianne Rissler and Gunnar Lindahl",
year = "1992",
language = "English",
volume = "89",
pages = "8661--8665",
journal = "Proceedings of the National Academy of Sciences",
issn = "1091-6490",
publisher = "National Acad Sciences",
number = "18",