1E4M

MYROSINASE FROM SINAPIS ALBA

Summary for 1E4M

• Entry DOI: 10.2210/pdb1e4m/pdb
• Related: 2MYR
• Descriptor: MYROSINASE MA1, 2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose, beta-D-xylopyranose-(1-2)-beta-D-mannopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-[alpha-L-fucopyranose-(1-3)]2-acetamido-2-deoxy-beta-D-glucopyranose, ... (9 entities in total)
• Functional Keywords: hydrolase, family 1 glycosyl hydrolase, glucosinolate, tim barrel
• Biological source: SINAPIS ALBA (WHITE MUSTARD)
• Total number of polymer chains: 1
• Total formula weight: 62178.20

Authors

Burmeister, W.P. (deposition date: 2000-07-10, release date: 2001-05-25, Last modification date: 2024-10-23)

Primary citation

Burmeister, W.P.,Cottaz, S.,Rollin, P.,Vasella, A.,Henrissat, B.
High Resolution X-Ray Crystallography Shows that Ascorbate is a Cofactor for Myrosinase and Substitutes for the Function of the Catalytic Base
J.Biol.Chem., 275:39385-, 2000

PubMed Abstract: 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.

PubMed: 10978344
DOI: 10.1074/JBC.M006796200

Experimental method

X-RAY DIFFRACTION (1.2 Å)