Peptides derived from human C-reactive protein inhibit the enzymatic activities of human leukocyte elastase and cathepsin G: use of overlapping peptide sequences to identify a unique inhibitor.

Ten overlapping 15-mer peptides, spanning the entire inner disulfide loop of human C-reactive protein (residues 36-97), were used to isolate a potent inhibitor of the enzymes human leukocyte elastase and human leukocyte cathepsin G, which are associated with chronic inflammatory tissue damage. In contrast to the inability of intact C-reactive protein to inhibit both enzymes, the synthetic peptide E62ILIFWSKDIGYSFT76 inhibited leukocyte elastase (Ki = 0.18 microM) and cathepsin G (Ki = 0.25 microM) at concentrations far lower than the acute-phase concentration of C-reactive protein. Several peptide-enzyme binding motifs were elucidated by structure-function studies, with the Glu62 residue being crucial in establishing long-range subsite interactions. Peptides derived from C-reactive protein, which may be generated in vivo by neutrophil-mediated proteolysis as part of a complex regulatory homeostatic mechanism, may play an important role in regulating the activity of matrix-degrading enzymes, specifically at sites of inflammation. The present results thus may shed additional insight on the physiological functions of the major acute-phase reactant C-reactive protein, and perhaps be used as a basis for the design of novel therapeutic substances.