title: Studies of inhibitory mechanisms of propeptide-like cysteine protease inhibitors.
abstract: Mouse cytotoxic T-lymphocyte antigen-2α (CTLA-2α), Drosophila CTLA-2-like protein (crammer), and Bombyx cysteine protease inhibitor (BCPI) belong to a novel family of cysteine protease inhibitors (I29). Their inhibitory mechanisms were studied comparatively. CTLA-2α contains a cysteine residue (C75), which is essential for its inhibitory potency. The CTLA-2α monomer was converted to a disulfide-bonded dimer in vitro and in vivo. The dimer was fully inhibitory, but the monomer, which possessed a free thiol residue, was not. A disulfide-bonded CTLA-2α/cathepsin L complex was isolated, and a cathepsin L subunit with a molecular weight of 24,000 was identified as the interactive enzyme protein. Crammer also contains a cysteine residue (C72). Both dimeric and monomeric forms of crammer were inhibitory. A crammer mutant with Cys72 to alanine (C72A) was fully inhibitory, while the replacement of Gly73 with alanine (G73A) caused a significant loss in inhibitory potency, which suggests a different inhibition mechanism from CTLA-2α. BCPI does not contain cysteine residue. C-terminal region (L77-R80) of BCPI was essential for its inhibitory potency. CTLA-2α was inhibitory in the acidic pH condition but stabilized cathepsin L under neutral pH conditions. The different inhibition mechanisms and functional considerations of these inhibitors are discussed.
authors.affiliation: Laboratory of Biochemistry, Joint Faculty of Veterinary Science, Yamaguchi University, Yamaguchi 753-8515, Japan.
authors.forename: Bui T T
authors.initials: BT
authors.lastname: Nga
authors.affiliation: Laboratory of Biochemistry, Joint Faculty of Veterinary Science, Yamaguchi University, Yamaguchi 753-8515, Japan.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Takeshita
authors.affiliation: Faculty of Health Science, Yamaguchi University School of Medicine, Yamaguchi 755-8554, Japan.
authors.forename: Misa
authors.initials: M
authors.lastname: Yamamoto
authors.affiliation: Laboratory of Biochemistry, Joint Faculty of Veterinary Science, Yamaguchi University, Yamaguchi 753-8515, Japan.
authors.forename: Yoshimi
authors.initials: Y
authors.lastname: Yamamoto