Characterization of the allosteric anion-binding site of O-acetylserine sulfhydrylase

Citation
Ch. Tai et al., Characterization of the allosteric anion-binding site of O-acetylserine sulfhydrylase, BIOCHEM, 40(25), 2001, pp. 7446-7452
Citations number
14
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Biochemistry & Biophysics
Journal title
BIOCHEMISTRY
ISSN journal
0006-2960 → ACNP
Volume
40
Issue
25
Year of publication
2001
Pages
7446 - 7452
Database
ISI
SICI code
0006-2960(20010626)40:25<7446:COTAAS>2.0.ZU;2-U
Abstract
A new crystal structure of the A-isozyme of O-acetylserine sulfhydrylase-A (OASS) with chloride bound to an allosteric site located at the dimer inter face has recently been determined [Burkhard, P., Tai, C.-H., Jansonius, J. N., and Cook, P. F. (2000) J. Mel. Biol. 303, 279-286]. Data have been obta ined from steady state and presteady-state kinetic studies and from UV-visi ble spectral studies to characterize the allosteric anion-binding site. Dat a obtained with chloride and sulfate as inhibitors indicate the following: (i) chloride and sulfate prevent the formation of the external aldimines wi th L-cysteine or L-serine; (ii) chloride and sulfate increase the external aldimine dissociation constants for O-acetyl-L-serine, L-methionine, and 5- oxo-L-norleucine; (iii) chloride and sulfate bind to the allosteric site in the internal aldimine and alpha -aminoacrylate external aldimine forms of OASS; (iv) sulfate also binds to the active site. Sulfide behaves in a mann er identical to chloride and sulfate in preventing the formation of the L-s erine external. aldimine. The binding of chloride to the allosteric site is pH independent over the pH range 7-9, suggesting no ionizable enzyme side chains ionize over this pH range. Inhibition by sulfide is potent (K-d is 2 5 muM at pH 8) suggesting that SH- is the physiologic inhibitory species.