118492-82-3Relevant articles and documents
Sterol C24-methyltransferase: Physio- and stereo-chemical features of the sterol C3 group required for catalytic competence
Howard, Alicia L.,Liu, Jialin,Elmegeed, Gamal A.,Collins, Emily K.,Ganatra, Kalgi S.,Nwogwugwu, Chizaram A.,Nes, W. David
experimental part, p. 43 - 50 (2012/08/07)
Sterol C24-methyltransferases (24-SMTs) catalyze the electrophilic alkylation of Δ24-sterols to a variety of sterol side chain constructions, and the C3- moiety is the primary determinant for substrate binding by these enzymes. To determine what specific structural features of the C3-polar group ensure sterol catalysis, a series of structurally related C3-analogs of lanosterol that differed in stereochemistry, bulk and electronic properties were examined against the fungal 24-SMT from Paracoccidioides brasiliensis (Pb) which recognize lanosterol as the natural substrate. Analysis of the magnitude of sterol C24-methylation activity (based on the kinetic constants of Vmax/Km and product distributions determined by GC-MS) resulting from changes at the C3-position in which the 3β-OH was replaced by 3α-OH, 3β-acetyl, 3-oxo, 3-OMe, 3β-F, 3β-NH2 (protonated species) or 3H group revealed that lanosterol and five substrate analogs were catalyzed and yielded identical side chain products whereas neither the 3H- or 3α-OH lanosterol derivatives were productively bound. Taken together, our results demonstrate a chemical complementarity involving hydrogen bonding formation of specific active site contacts to the nucleophilic C3-group of sterol is required for proper orientation of the substrate C-methyl intermediate in the activated complex.
