Functional Identification of Triterpene Methyltransferases from Botryococcus braunii Race B

• DOI: 10.1074/jbc.m111.316059
• Publication Date: 2012-01-13T01:27:49Z
• Authors: Tom D. Niehaus; Scott Kinison; Shigeru Okada; Yun-soo Yeo; Stephen A. Bell; Ping Cui; Timothy P. Devarenne; Joe Chappell
• Keywords: Botryococcus braunii; Squalene

Botryococcus braunii race B is a colony-forming, green algae that accumulates triterpene oils in excess of 30% its dry weight. The composition the dominated by dimethylated to tetramethylated forms botryococcene and squalene. Although unusual mechanisms for biosynthesis squalene were recently described, enzyme(s) responsible decorating these scaffolds with methyl substituents unknown. A transcriptome B. was screened computationally assuming methyltransferases (TMTs) might resemble S-adenosyl methionine-dependent enzymes described methylating side chain sterols. Six sterol methyltransferase-like genes isolated functionally characterized. Three when co-expressed yeast complementary synthase or expression cassettes resulted accumulation mono- both scaffolds. Surprisingly, TMT-1 TMT-2 exhibited preference as acceptor substrate, whereas TMT-3 showed striking substrate. These vivo preferences confirmed vitro assays utilizing microsomal preparations from overexpressing respective genes, which encode membrane-associated enzymes. Structural examination generated products NMR identified terminal carbons, C-3 C-22/C-20, atomic sites additions botryococcene, respectively. are identical those previously reported triterpenes extracted algae. availability closely related exhibiting distinct substrate selectivity successive catalytic activities provides important tools investigating molecular specificities unique