Nonhistone protein purified from porcine kidney acts as a suicide substrate inhibitor on furin-like enzyme

AIM: To search and purify;a naturally occurring protein inhibitor of the fu rin-like enzyme from the porcine kidney. METHODS: Recombinant kexin, a furi n-like enzyme, from the yeast secretion expression was used as a target enz yme. The inhibitor component was extracted and purified from the acetone po wder of porcine kidney. The inhibitory activity was monitored using a fluor ogenic peptide substrate Boc-Arg-Val-Arg-Arg-MCA at spectrofluorimeter. RES ULTS: The purified inhibitor component is a basic protein with an isoelectr ic point over 9.5. Its partial N-terminal sequence of 22 residues was deter mined, showing a high homology with nonhistone chromosomal protein HMG-17 i n which there are four sites composed of dibasic residues, susceptible to b e cleaved by the furin-like enzyme. This nonhistone protein could strongly compete with the fluorogenic substrate. However, this nonhistone protein wo uld be degraded as a substrate by kexin if it was incubated with the enzyme for long time before adding the fluorogenic substrate, and subsequently lo st its temporary inhibitory activity. CONCLUSION: The nonhistone protein is olated from the porcine kidney functioned as a suicide substrate inhibitor for the furin-like enzyme.