ELECTROPHORETIC ANALYSIS OF THE CROSS-CLASS INTERACTION BETWEEN NOVELINHIBITORY SERPIN, SQUAMOUS-CELL CARCINOMA ANTIGEN-1 AND CYSTEINE PROTEINASES

We investigated the ''cross-class'' interaction between cysteine prote inases and a novel inhibitory serpin, recombinant squamous cell carcin oma (rSCC) antigen-1, which inhibits a serine proteinase, chymotrypsin , rSCC antigen-1 inhibited the cysteine proteinases, papain, papaya pr oteinase IV and cathepsin L. Interestingly, although rSCC antigen-1 fo rmed sodium dodecyl sulfate (SDS)and heat-stable complexes with chymot rypsin, rSCC antigen-1 gave the 40 kDa fragment and small molecular ma ss peptide by incubation with papain without forming an SDS- and heat- stable complex. The cleavage was observed between the Gly(353)-Ser(354 ) bond, indicating that rSCC antigen-1 interacts with cysteine protein ases not at the predicted reactive site P1-P1' portion (Ser(354)-Ser(3 55)), but at the Gly(353)-Ser(354) of the P2-P1 portion. These finding s promote understanding of the ''suicide inhibition'' mechanism of SCC antigen-1 against cysteine proteinases.