Cleavage of Protein A-Binding IgAl with IgAl Protease from Streptococcus Sanguis

Abstract

Protein A-binding fractions of two IgAl myeloma proteins failed to produce Fc fragments on digestion with IgAl protease from Streptococcus sanguis. A polymeric protein A-binding IgAl fraction yielded a protein A-non-binding monomer, which was further cleaved into Fab fragments but it did not yield Fc fragments. The protein A-binding fraction of a monomeric IgAl yielded an IgA molecule lacking one Fab fragment. Subsequently, the remaining part of its cleaved α chain was degraded. Further digestion yielded Fab but not Fc fragments. Similarly, F(abc)₂ and Fabc fragments, which lack the C_H3 domain (8), yielded Fab fragments but not C_H2 domains. Thus, the enzyme in addition to cleaving IgA in the hinge region, under certain conditions, also degrades its Fc fragments.