88902-03-8Relevant articles and documents
Specific production of γ-polypodatetraene or 17-isodammara-20(21),24-diene by squalene-hopene cyclase mutant
Schmitz, Susanne,Füll, Christine,Glaser, Tobias,Albert, Klaus,Poralla, Karl
, p. 883 - 885 (2001)
Amino acids lining the catalytic cavity of squalene-hopene cyclase of Alicyclobacillus acidocaldarius were mutated to investigate their catalytic functions. Mutagenesis of Leu607 to Lys in the central part of the cavity resulted in the production of the b
Functional analyses of Tyr420 and Leu607 of Alicyclobacillus acidocaldarius squalene-hopene cyclase. Neoachillapentaene, a novel triterpene with the 1,5,6-trimethylcyclohexene moiety produced through folding of the constrained boat structure
Sato, Tsutomu,Sasahara, Shigehiro,Yamakami, Toshiyuki,Hoshino, Tsutomu
, p. 1660 - 1670 (2007/10/03)
The functions of Tyr420 and Leu607 were analyzed by constructing various site-directed mutants. The mutation at position 420 into Ala and Gly gave bicyclic α-and γ-polypodatetraene in significant amounts, but with a trace amount of tricyclic malabaricatriene. The kinetic data for and the product distribution of the Y420F mutant indicate that the major function of Tyr420 is to stabilize the 6/6-fused bicyclic cation. Mutation experiments on Leu607 demonstrate that the appropriate steric bulk size at position 607 is required to strongly bind with the product-like conformation formed during the polycyclization process. Introduction of the bulkiest Trp residue into 420 or 607 led to the production of a novel monocyclic triterpene having the (5R,6R)-1,5,6-trimethylcyclohexene ring, named neoachillapentaene, indicating that the enzymatic cyclization proceeded via a constrained boat structure. Folding of the squalene molecule into a boat conformation by squalene cyclase has not been reported before.
Catalytic function of the residues of phenylalanine and tyrosine conserved in squalene-hopene cyclases.
Sato,Hoshino
, p. 2233 - 2242 (2007/10/03)
Site-directed mutagenesis experiments on all the conserved residues of Phe and Tyr in all the known squalene-hopene cyclases (SHCs) were carried out to identify the active site residues of thermophilic Alicyclobacillus acidocaldarius SHC. The following functions are proposed on the basis of kinetic data and trapping of the prematurely cyclized products: (1) The Y495 residue probably amplifies the D376 acidity, which is assumed to work as a proton donor for initiating the polycyclization cascade, but its role is moderate. (2) Y609 possibly assists the function of F365, which has previously been assigned to exclusively stabilize the C-8 carbocation intermediate through cation-pi interaction. The Y609A mutant produced a partially cyclized bicyclic triterpene. (3) Y612 works to stabilize both the C10 and C8 carbocations, this being verified by the finding that mono- and bicyclic products were formed with the Y612A mutant. (4) F129 was first identified to play a crucial role in catalysis. (5) The three residues, Y372, Y474 and Y540, are responsible for reinforcing the protein structure against thermal denaturation, Y474 being located inside QW motif 3.
