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 C7 or C11.
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 C6-Me leads to an efficient polycyclization cascade. Substitution of the C14-H and the C18-H 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 C7-H and the C11-H 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.
Nakano
Shin-Ichi
S
Department of Applied Biological Chemistry, Faculty of Agriculture, and Graduate School of Science and Technology, Niigata University, Ikarashi, Niigata 950-2181, Japan.
Ohashi
Shumi
S
Hoshino
Tsutomu
T
D003500:Cyclization; D019751:Intramolecular Transferases / Q000737:chemistry*; D015394:Molecular Structure; D011994:Recombinant Proteins / Q000737:chemistry; D013185:Squalene / Q000031:analogs & derivatives* / Q000138:chemical synthesis* / Q000737:chemistry; D013237:Stereoisomerism
D011994:Recombinant Proteins; D013185:Squalene; D019751:Intramolecular Transferases; C066630:squalene-hopene cyclase