Identification of Interaction Site of Propeptide toward Mature Carboxypeptidase Y (mCPY) Based on the Similarity between Propeptide and CPY Inhibitor (I^C)

Abstract

Both the propeptide in the precursor carboxypeptidase Y (proCPY) and the mature CPY (mCPY)-specific endogenous inhibitor (I^C) inhibit CPY activity. The N-terminal inhibitory reactive site of I^C (the N-terminal seven amino acids of I^C) binds to the substrate-binding site of mCPY and is essential for mCPY inhibition, but the mechanism of mCPY inhibition by the propeptide is poorly understood. In this study, sequence alignment between I^C and proCPY indicated that a sequence similar to the N-terminal region of I^C was present in proCPY. In particular, a region including the C-terminus of the propeptide was similar to the N-terminal seven amino acids of I^C. In the presence of peptides identical to the N-terminus of I^C and the C-terminus of the propeptide, CPY activity was competitively inhibited. The C-terminal region of the propeptide might bind to the substrate-binding site of mCPY.