Saxiphilin, a saxitoxin-binding protein with two thyroglobulin type 1 domains, is an inhibitor of papain-like cysteine proteinases

Citation
B. Lenarcic et al., Saxiphilin, a saxitoxin-binding protein with two thyroglobulin type 1 domains, is an inhibitor of papain-like cysteine proteinases, J BIOL CHEM, 275(20), 2000, pp. 15572-15577
Citations number
45
Categorie Soggetti
Biochemistry & Biophysics
Journal title
JOURNAL OF BIOLOGICAL CHEMISTRY
ISSN journal
00219258 → ACNP
Volume
275
Issue
20
Year of publication
2000
Pages
15572 - 15577
Database
ISI
SICI code
0021-9258(20000519)275:20<15572:SASPWT>2.0.ZU;2-A
Abstract
The type 1 domain of thyroglobulin is a protein module (Thyr-1) that occurs in a variety of secreted and membrane proteins. Several examples of Thyr-1 modules have been previously identified as inhibitors of the papain family of cysteine proteinases, Saxiphilin is a neurotoxin-binding protein from b ullfrog and a homolog of transferrin with a pair of such Thyr-1 modules loc ated in the N-lobe. Saxiphilin is now characterized as a potent inhibitor o f three cysteine proteinases as follows: papain, human cathepsin B, and cat hepsin L, The stoichiometry of enzyme inhibition reveals that both Thyr-1 d omains of saxiphilin inhibit papain (apparent K-i = 1.72 naa), but only one of these domains inhibits cathepsin B (K-i = 1.67 nM) and cathepsin L (K-i = 0.02 nM). Physical association of saxiphilin and papain blocked from tur nover at the active-site cysteine residue can be detected by cross-linking with glutaraldehyde. The rate of association of saxiphilin and cathepsin B is strongly pH-dependent with an optimum at pH 5.2, reflecting control by a t least two H+-titratable groups. These results further demonstrate that va rious Thyr-1 domains are selective inhibitors of cysteine proteinases with utility in the study of protein interactions and degradation.