Bombyx cysteine proteinase inhibitor (BCPI) homologous to propeptide regions of cysteine proteinases is a strong, selective inhibitor of cathepsin L-like cysteine proteinases
M. Kurata et al., Bombyx cysteine proteinase inhibitor (BCPI) homologous to propeptide regions of cysteine proteinases is a strong, selective inhibitor of cathepsin L-like cysteine proteinases, J BIOCHEM, 130(6), 2001, pp. 857-863
Bombyx cysteine proteinase inhibitor (BCPI) is a novel cysteine proteinase
inhibitor. The protein sequence is homologous to the proregions of certain
cysteine proteinases. Here we report the mechanism of its inhibition of sev
eral cysteine proteinases. BCPI strongly inhibited Bombyx cysteine proteina
se (BCP) activity with a K-i = 5.9 muM, and human cathepsin L with a K-i =
36 muM. The inhibition obeyed slow-binding kinetics. The inhibition of cath
epsin H was much weaker (K-i = 82 nm), while inhibition of papain (K-i > 1
muM) and cathepsin B (K-i > 4 muM) was negligible. Following incubation wit
h BCP, BCPI was first truncated at the C-terminal end, and then gradually d
egraded over time. The truncation mainly involved two C-terminal amino acid
residues. Recombinant BCPI lacking the two C-terminal amino acid residues
still retained substantial inhibitory activity. Our results indicate that B
CPI is a stable and highly selective inhibitor of cathepsin L-like cysteine
proteinases.