The site of cleavage in human alpha chains of IgA1 and IgA2:A2m(1) allotype paraproteins by the clostridial IgA protease

Abstract

Fc fragments of human immunoglobulin A(IgA) of IgAl subclass and IgA2 subclass of A2m(1) allotype were prepared from IgA paraproteins by digestion with a protease from Clostridium sp. (M.O.-6). The N-terminal tetrapeptide of Val-Pro-Ser-Thr- for the Fc of IgA1 subclass, and that of Val-Pro-Pro-Pro- for the Fc of IgA2:A2m(1) allotype, were identified by sequence analysis. The site of cleavage by the protease was defined to be at the Pro-Val peptide bond, which is a common peptide bond present at 221–222 in both alpha chains. IgA of IgA2 subclass of A2m(2) allotype is resistent to the protease due to the different, Arg-Val, peptide bond at the same position.