Staphylococcal protein A and human IgG subclasses and allotypes.
Staphylococcal protein A binds molecules belonging to the IgG1, IgG2, and IgG4 subclasses. IgG3 proteins generally do not bind, except for those coded by the two gamma 3 alleles, which are G3m(u-): G3m(b0,b3,b5,s,v). G3m(u) is located in the CH2 domain. The difference between G3m(u-) and G3m(u+) IgG3 proteins correlates with the sequence at position 339 in the CH2 domain--Ala and Thr respectively. There is another structural difference in the CH3 domain which correlates with protein A binding and non-binding: all IgG proteins that bind protein A have His at position 435, whereas those that do not, have Arg at that position.
D000483:Alleles; D000595:Amino Acid Sequence; D001666:Binding Sites, Antibody; D006801:Humans; D007126:Immunoglobulin Allotypes / Q000235:genetics / Q000276:immunology*; D007074:Immunoglobulin G / Q000235:genetics / Q000276:immunology*; D013205:Staphylococcal Protein A / Q000276:immunology*
D007126:Immunoglobulin Allotypes; D007074:Immunoglobulin G; D013205:Staphylococcal Protein A