Functional Analysis of the DXDDTA Motif in Squalene-Hopene Cyclase by Site-directed Mutagenesis Experiments : Initiation Site of the Polycyclization Reaction and Stabilization Site of the Carbocation Intermediate of the Initially Cyclized A-Ring

概要

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In order to clarify the function of the DXDDTA motif in squalene-hopene cyclase and to identify the acidic amino acid residues crucial for the catalysis, site-directed mutagenesis experiments were carried out. The following results were found : (1) residues D374 and D376 work for the initiation of polyolefin cyclization which arises from the proton attack on the terminal double bond ; (2) residue D377 stabilizes C-10 carbocation of the initially cyclized A-ring intermediate, leading to subsequent B-ring closure, which was further verified by isolating the partially cyclized monocyclic product ; (3) residues D313 and D447 outside the DXDDTA motif were identified as new active sites ; (4) the H451 residue is likely to work in the protonated form to enhance the acidity of the carboxyl groups of D374 and/or D376.
社団法人日本農芸化学会の論文
1999-12-23