Distinct cleavage specificity of human cathepsin E at neutral pH with special preference for Arg-Arg bonds

In order to clarify the potential role of cathepsin E at neutral pH, the cleavage specificity of human cathepsin E was examined at pH 7.4 toward reduced-carboxymethylated(RCm-)ribonuclease A and various bioactive and related peptides. The specificity of the enzyme at pH 7.4 was found to be considerably different from that at acidic pH; preferential cleavages were observed with Arg-X and Glu-X bonds, which are not the major cleavage sites at acidic pH. Moreover, the Arg-Arg bond was found to be the most preferential site of cleavage. This unique specificity observed at pH 7.4 suggests the possibility that cathepsin E might be involved in processing and/or degradation of certain proteins and/or peptides at or near neutral pH in vivo.