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

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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 CH3 domain (8), yielded Fab fragments but not CH2 domains. Thus, the enzyme in addition to cleaving IgA in the hinge region, under certain conditions, also degrades its Fc fragments.