The type-III Fc receptor from Streptococcus dysgalactiae is also an alpha 2-macroglobulin receptor.
We have cloned and sequenced the gene for a type-III Fc receptor from a Streptococcus dysgalactiae strain isolated from bovine mastitis and report here the complete sequence of the gene. The 1992-nucleotides-long open reading frame codes for a protein of 664 amino acids with a predicted molecular mass of 72 kDa (including the signal peptide). The C-terminal part of the protein is very similar to other streptococcal type-III receptors but contains five homologous IgG-binding domains compared to two or three in earlier reported Fc receptors of this type. Upstream of the IgG-binding domains, there is a unique sequence containing short repeated motifs. Subcloning different parts of the gene and expressing them as maltose-binding fusion proteins revealed that the upstream part is mediating binding to the plasma proteinase inhibitor alpha 2-macroglobulin after its complex formation with proteases. In contrast to earlier described type-III Fc receptors, this molecule does not bind human serum albumin.
Jonsson
H
H
Department of Microbiology, Swedish University of Agricultural Sciences, Uppsala.
Müller
H P
HP
D000595:Amino Acid Sequence; D001483:Base Sequence; D001665:Binding Sites; D001667:Binding, Competitive; D003001:Cloning, Molecular; D005798:Genes, Bacterial; D026503:Low Density Lipoprotein Receptor-Related Protein-1; D008969:Molecular Sequence Data; D017452:Receptors, IgG / Q000737:chemistry* / Q000235:genetics; D011971:Receptors, Immunologic / Q000737:chemistry* / Q000235:genetics; D015183:Restriction Mapping; D013291:Streptococcus / Q000235:genetics / Q000276:immunology*
D026503:Low Density Lipoprotein Receptor-Related Protein-1; D017452:Receptors, IgG; D011971:Receptors, Immunologic