'''2-F-GLUCOSYLATED MYROSINASE FROM SINAPIS ALBA'''
===2-F-GLUCOSYLATED MYROSINASE FROM SINAPIS ALBA===
==Overview==
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Myrosinase, an S-glycosidase, hydrolyzes plant anionic 1-thio-beta-d-glucosides (glucosinolates) considered part of the plant defense system. Although O-glycosidases are ubiquitous, myrosinase is the only known S-glycosidase. Its active site is very similar to that of retaining O-glycosidases, but one of the catalytic residues in O-glycosidases, a carboxylate residue functioning as the general base, is replaced by a glutamine residue. Myrosinase is strongly activated by ascorbic acid. Several binary and ternary complexes of myrosinase with different transition state analogues and ascorbic acid have been analyzed at high resolution by x-ray crystallography along with a 2-deoxy-2-fluoro-glucosyl enzyme intermediate. One of the inhibitors, d-gluconhydroximo-1,5-lactam, binds simultaneously with a sulfate ion to form a mimic of the enzyme-substrate complex. Ascorbate binds to a site distinct from the glucose binding site but overlapping with the aglycon binding site, suggesting that activation occurs at the second step of catalysis, i.e. hydrolysis of the glycosyl enzyme. A water molecule is placed perfectly for activation by ascorbate and for nucleophilic attack on the covalently trapped 2-fluoro-glucosyl-moiety. Activation of the hydrolysis of the glucosyl enzyme intermediate is further evidenced by the observation that ascorbate enhances the rate of reactivation of the 2-fluoro-glycosyl enzyme, leading to the conclusion that ascorbic acid substitutes for the catalytic base in myrosinase.
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{{ABSTRACT_PUBMED_10978344}}
==About this Structure==
==About this Structure==
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[[Category: Myrosinase]]
[[Category: Myrosinase]]
[[Category: Tim barrel]]
[[Category: Tim barrel]]
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 14:44:43 2008''
''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Tue Jul 1 00:15:27 2008''
Revision as of 00:15, 1 July 2008
This article has been automatically seeded. Changes to this page should pertain to the PDB entry only and not to the protein or biomolecule in general.
This structure supersedes the now removed PDB entry 2myr. Full crystallographic information is available from OCA.
ReferenceReference
High resolution X-ray crystallography shows that ascorbate is a cofactor for myrosinase and substitutes for the function of the catalytic base., Burmeister WP, Cottaz S, Rollin P, Vasella A, Henrissat B, J Biol Chem. 2000 Dec 15;275(50):39385-93. PMID:10978344
