Sterol C24-methyltransferase: Physio- and stereo-chemical features of the sterol C3 group required for catalytic competence

详细信息	查看全文 | 推荐本文 |

• 作者：Alicia L. Howard¹ ; Jialin Liu¹ ; Gamal A. Elmegeed² ; Emily K. Collins³ ; ⁴ ; Kalgi S. Ganatra⁴ ; Chizaram A. Nwogwugwu⁴ ; W. David Nes ; ^{wdavid.nes@ttu.edu}
• 关键词：Sterol C24-methyltransferase ; Lanosterol ; Fluorinated sterol ; Sterol catalysis ; Hydrogen bonding ; Paracoccidioides brasiliensis
• 刊名：Archives of Biochemistry and Biophysics
• 出版年：2012
• 期刊代码：116_00039861
• 类别：ch
• 出版时间：May, 2012
• 卷：521
• 期：1-2
• 页码：43-50
• 文件大小：674 K

摘要

Sterol C24-methyltransferases (24-SMTs) catalyze the electrophilic alkylation of 螖²⁴-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 V_max/K_m and product distributions determined by GC-MS) resulting from changes at the C3-position in which the 3尾-OH was replaced by 3伪-OH, 3尾-acetyl, 3-oxo, 3-OMe, 3尾-F, 3尾-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 3伪-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.