7S immunoglobulins of a monotreme, the Echidna Tachyglossus aculeatus: two distinct isotypes which bind A protein of Staphylococcus aureus

Abstract

7S immunoglobulins of a monotreme mammal, the echidna Tachyglossus aculeatus, bind to Staphylococcus aureus A protein coupled to an insoluble matrix. This binding supports the homology between the previously described echidna IgG and IgG molecules of higher mammals and provides a rapid, simple method for the isolation of this protein from echidna serum. In addition, another echidna 7S immunoglobulin became bound to protein A-Sepharose. The major protein A-binding immunoglobulin has a slow electrophoretic mobility and possesses a heavy chain comparable in mass to typical mammalian γ chains (52,000 daltons). We suggest the designation IgG2 for this immunoglobulin. The minor protein A-binding immunoglobulin is electrophoretically faster than IgG2 and can be resolved from the former by gradient elution from DEAE-Biogel. We propose the nomenclature IgG1 for this molecule although we cannot discount the possibility that it might represent another main class such as IgA. The γ1 heavy chain is distinguishable from the γ2 chain on polyacrylamide gel electrophoresis in sodium dodecylsulphate containing buffers. The γ1 chain possesses a nominal mass of 61,000 daltons. The intact molecule has an apparent mass of 177,000 Daltons and comprises two pairs of light and heavy chains.