title: Species-dependent post-translational modification and position 2 allelism: effects on streptococcal superantigen SSA structure and V beta specificity.
abstract: Epidemiologic and molecular population genetic analyses support a role for superantigens (SAg) in the pathogenesis of severe staphylococcal and streptococcal infections. To investigate how variations in SAg structure influence immunomodulatory activity, we examined the biochemical and functional properties of two allelic variants of streptococcal SAg SSA that differ at position 2. Mass spectrometry revealed both recombinant (Escherichia coli) and native (Streptococcus pyogenes) SSA allelic variants to have significantly larger molecular masses than predicted by primary sequence alone and provided evidence that the proteins were modified by the addition of biochemical moieties, a phenomenon that has not been described for related SAg. Furthermore, the molecular masses of native and recombinant SSA were not the same; SSA was differentially post-translationally modified by the two bacterial genera. The substitution of E. coli-dependent processing for that of S. pyogenes altered both protease digestion and V beta specificity, suggesting that recombinant SAg from E. coli may not accurately represent the native toxin. In addition, the observation that SSA allelic variants differed in V beta specificity supports a role for position 2 in SSA-TCR interactions. That SSA position 2 contributes to V beta specificity could not have been predicted from functional or crystallographic studies of other SAg and suggests that SSA may adopt unique interactions with TCR and/or MHC class II molecules. Determining the structural basis for these differences should offer additional clues to the manner in which SAg exert their effects on the immune system during infection and may allow the designing of SAg mutants with specific quantitative and qualitative immunomodulatory properties.
authors.affiliation: Department of Microbiology, Baylor College of Medicine, Houston 77030, USA.
authors.forename: K R
authors.initials: KR
authors.lastname: Stevens
authors.forename: M
authors.initials: M
authors.lastname: Van
authors.forename: J G
authors.initials: JG
authors.lastname: Lamphear
authors.forename: R S
authors.initials: RS
authors.lastname: Orkiszewski
authors.forename: K D
authors.initials: KD
authors.lastname: Ballard
authors.forename: R G
authors.initials: RG
authors.lastname: Cook
authors.forename: R R
authors.initials: RR
authors.lastname: Rich
mesh_terms: D000478:Alkylation; D000483:Alleles; D000595:Amino Acid Sequence; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics; D000942:Antigens, Bacterial / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D001667:Binding, Competitive / Q000276:immunology; D003546:Cysteine Endopeptidases / Q000494:pharmacology; D004306:Dose-Response Relationship, Immunologic; D004591:Electrophoresis, Polyacrylamide Gel; D000939:Epitopes / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D007739:L Cells; D008213:Lymphocyte Activation; D013058:Mass Spectrometry; D051379:Mice; D008934:Mitogens / Q000494:pharmacology; D008970:Molecular Weight; D010084:Oxidation-Reduction; D011499:Protein Processing, Post-Translational / Q000276:immunology*; D011994:Recombinant Proteins / Q000276:immunology / Q000378:metabolism; D013045:Species Specificity; D013297:Streptococcus pyogenes / Q000235:genetics / Q000276:immunology*; D018089:Superantigens / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism; D013601:T-Lymphocytes / Q000276:immunology
chemical_list: D000942:Antigens, Bacterial; D000939:Epitopes; D008934:Mitogens; D011994:Recombinant Proteins; D018089:Superantigens; D003546:Cysteine Endopeptidases; C067046:gingivain