Identification of a mycoplasmal protein which binds immunoglobulins nonimmunologically

Immunoblotted protein samples from several strains of Mycoplasma hominis and from one strain of Mycoplasma arginini each contain a polypeptide of a molecular mass of 95,000 to 105,000 Da which binds immunoglobulin nonimmunologically. Immunoblots from these organisms were probed with alkaline phosphatase-conjugated goat anti-rabbit immunoglobulin, conjugated goat immunoglobulin G (IgG) Fab fragments, and conjugated goat IgG Fc fragments. The polypeptide bound the goat anti-rabbit molecules and the Fab fragments but not the Fc fragments. These reactions could be blocked with nonimmune unconjugated goat IgG and unconjugated human IgM. Controls probed with alkaline phosphatase alone did not stain. Binding of the conjugated preparations to whole mycoplasmal cells was dependent on concentrations of both conjugate and cells for the goat anti-rabbit preparation and for Fab. The mycoplasmal polypeptide may be a light-chain-specific reactant.