Squalene–hopene cyclase: insight into the role of the methyl group on the squalene backbone upon the polycyclization cascade. Enzymatic cyclization products of squalene analogs lacking a 26-methyl group and possessing a methyl group at C(7) or C(11)
作者:Shin-ichi Nakano、Shumi Ohashi、Tsutomu Hoshino
DOI:10.1039/b404287e
日期:——
To provide deep insight into the polycyclization reaction of squalene, some analogs were synthesized and incubated with the cell-free homogenates of the recombinant Escherichia coli encoding the wild-type squalene cyclase. The presence of C(6)âMe leads to an efficient polycyclization cascade. Substitution of the C(14)âH and the C(18)âH with a methyl group halted the polycylization reaction at the tricyclic ring stage having a 6/6/6-fused ring system and the tetracycle with a 6/6/6/6-fused ring, respectively, both of which were produced according to a Markovnikov closure. Replacement of the C(7)âH and the C(11)âH with a methyl group led to no cyclization. These results, in conjunction with our previous reports, indicated that the methyl positions are important for bringing to completion of the normal polycylization reaction and further demonstrated that the precise steric bulk size at the methyl positions of squalene is critical to the correct folding and the strong binding of the substrate to the squalene cyclase.
为了深入了解鲨烯的多环化反应,合成了一些类似物,并与编码野生型鲨烯环化酶的重组大肠杆菌的无细胞匀浆一起孵育。C(6)–Me的存在导致了一个高效的多环化级联反应。用甲基取代C(14)–H和C(18)–H分别使多环化反应在具有6/6/6融合环系统的三环阶段和具有6/6/6/6融合环的四环阶段停止,这两者都是按照马克尼科夫闭合反应生成的。用甲基替代C(7)–H和C(11)–H则未导致环化。结合我们之前的报告,这些结果表明甲基位置对正常多环化反应的完成至关重要,并进一步证明鲨烯中甲基位置的精确立体体积对于底物与鲨烯环化酶的正确折叠和强结合至关重要。