Purification and characterization of M3 protein expressed on the surface of group A streptococcal type 3 strain C203

Characterization of group a streptococcal M23 protein and comparison of the M3 and M23 protein's ligand-binding domains

The present study concerns the properties for binding of human plasma and extracellular matrix proteins and the relationship between M3 and M23 molecules. Here, it is demonstrated that M23 protein shows a multiple binding to fibrinogen (FG), fibronectin (FN), human serum albumin (HSA), immunoglobulin G (IgG), kininogen, and collagen type I (CI) in Western blot analysis. Some sets of truncated-recombinant M3 or M23 protein fragments were assayed for their capacity to bind FN, FG, IgG, HSA, and CI. The HSA binding activity resided in the C-repeat region of M3 protein, whereas fibrinogen-binding activity resided in the A-repeat region. The FG, FN, and IgG binding sites were mapped to the N-terminal portion of M23 protein, whereas HSA binding was localized in the B-repeat domain, which has homology with C-repeat domain in M3 molecule. Therefore, it is concluded that the FN, FG, and IgG binding regions in the M3 and M23 proteins are quite dissimilar at the amino acid sequence level, whereas HSA binding is localized to the conserved C-repeat domain in the M3 and M23 proteins.

Characterization of group A streptococcal strains Sv and Su: determination of emm gene typing and presence of small vir regulon

The emm gene typing of GAS (group A streptococcus) strains Sv and Su and the molecular structure of the vir regulon were decided. An emm(-like) gene from the chromosomal DNA of GAS strain Sv was amplified with forward and reverse primers, which were selected from the best conserved portion in leader sequences of different strains and the C-terminal conserved portion, respectively, for determination of the M protein gene type. Strain Sv was defined as serotype M23, because deduced N-terminal amino acid positions of the products are identical to those of the M type 23 (emml) gene derived from GAS strain M23-MEMPHIS (M serotype 23, GenBank accession number U11953). When the vir regulon of strain Sv was examined by polymerase chain reaction mapping and compared with that of GAS strain Su, they had a similar size in length. In addition, when sequencing analysis of the DNA fragment of 4791 base pairs (bp) encoding three open reading frames (orf, mga, and emm) and the upstream region of scpA from genomic DNAs of both strains was performed, the sequence of the DNA from strain Sv was, except for 1 bp (T for C at position 4124), identical to that of the DNA from strain Su. These data show that both strains possess the genes in the order of mga (virR or mry) -emm -scpA designated as the small vir regulon. The effect of the formation of alternative pathway C3 convertase of complement on the GAS strains Sv and Su was also examined. When GAS strains Sv and Su were incubated in NHS containing radiolabeled C3 in the presence of Mg-EGTA, binding of C3 to Su bacteria was dose-dependent, whereas less binding of C3 to Sv bacteria was seen. Taken together, the data suggest that M protein could be expressed on the surface of the Sv bacteria, but not on the Su bacteria.

Human IgG binding ability of streptococcal M3 protein: its related complement activation-dependent M3 protein polymerization

We previously showed that M3 protein bound both fibrinogen and human serum albumin. Here, I report that M3 protein also has affinity for human immunoglobulin G. In contrast, M3 protein did not show affinity for polyclonal immunoglobulin G from other mammalian species (rabbit and goat). On the human immunoglobulin G molecule, the Fab domain was mainly responsible for the interaction with M3 protein, although the Fc region had a low degree of interaction with the M3 protein. Also, since the 35 kDa C-terminal fragment of M3 protein bound human immunoglobulin G, the binding site for human immunoglobulin G on M3 protein is present in this portion of the protein. The M3 protein-human immunoglobulin G complexes initiated complement activation via both classical and alternative pathways in normal human serum. When C3 was precipitated in the fluid phase with anti-C3 antibody and analyzed by SDS-PAGE under reducing conditions, M3 protein coprecipitated with the complexes and was polymerized. However, there was no polymerization of M3 protein when incubated with normal human serum treated with magnesium-ethyleneglycol-bis-(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid in the presence of M3 protein. Thus, this polymerization is mostly mediated via the classical activation pathway. It is probably helpful for the understanding of the antiphagocytic activity of M protein.