1e71: Difference between revisions
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==Overview== | ==Overview== | ||
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 ... | 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. | ||
==About this Structure== | ==About this Structure== | ||
1E71 is a | 1E71 is a [http://en.wikipedia.org/wiki/Protein_complex Protein complex] structure of sequences from [http://en.wikipedia.org/wiki/Sinapis_alba Sinapis alba] with NAG, ZN, SO4, ASC and GOL as [http://en.wikipedia.org/wiki/ligands ligands]. Active as [http://en.wikipedia.org/wiki/Transferred_entry:_3.2.1.147 Transferred entry: 3.2.1.147], with EC number [http://www.brenda-enzymes.info/php/result_flat.php4?ecno=3.2.3.1 3.2.3.1] Structure known Active Sites: ACT, ASC and ZNB. Full crystallographic information is available from [http://ispc.weizmann.ac.il/oca-bin/ocashort?id=1E71 OCA]. | ||
==Reference== | ==Reference== | ||
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[[Category: tim barrel]] | [[Category: tim barrel]] | ||
''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on | ''Page seeded by [http://ispc.weizmann.ac.il/oca OCA ] on Mon Nov 5 12:58:12 2007'' | ||
Revision as of 13:52, 5 November 2007
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MYROSINASE FROM SINAPIS ALBA WITH BOUND ASCORBATE
OverviewOverview
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.
About this StructureAbout this Structure
1E71 is a Protein complex structure of sequences from Sinapis alba with NAG, ZN, SO4, ASC and GOL as ligands. Active as Transferred entry: 3.2.1.147, with EC number 3.2.3.1 Structure known Active Sites: ACT, ASC and ZNB. 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
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