An Unusual Skeletal Rearrangement in the Biosynthesis of the Sesquiterpene Trichobrasilenol from Trichoderma

Abstract

The skeletons of some classes of terpenoids are unusual in that they contain a larger number of Me groups (or their biosynthetic equivalents such as olefinic methylene groups, hydroxymethyl groups, aldehydes, or carboxylic acids and their derivatives) than provided by their oligoprenyl diphosphate precursor. This is sometimes the result of an oxidative ring‐opening reaction at a terpene‐cyclase‐derived molecule containing the regular number of Me group equivalents, as observed for picrotoxan sesquiterpenes. In this study a sesquiterpene cyclase from Trichoderma spp. is described that can convert farnesyl diphosphate (FPP) directly via a remarkable skeletal rearrangement into trichobrasilenol, a new brasilane sesquiterpene with one additional Me group equivalent compared to FPP. A mechanistic hypothesis for the formation of the brasilane skeleton is supported by extensive isotopic labelling studies.

Biosynthesis of oxygenated brasilane terpene glycosides involves a promiscuous N-acetylglucosamine transferase

“…The product of BraA in A. oryzae NSAR1 could neither be unambiguously detected by HPLC-MS nor GCMS in our experimental setup. As all isolated brasilanes show the same absolute configuration as reported by Murai et al 9 and because BraA is highly similar to TaTC6 (Fig. S3, ESI †), it can be assumed that the terpene alcohol trichobrasilenol 4 is the most likely product of BraA.…”

“…The respective fragmentation pattern corresponds well with those previously reported for trichobrasilenol. 9 Based on these results, the full biosynthetic pathway towards 2 and 3 can be deduced (Fig. 1A), starting by the activity of BraA, which converts farnesyl pyrophosphate into the sesquiterpene alcohol 4.…”

“…[3][4][5][6][7][8] Recently, two groups have independently reported the characterisation of the terpene cyclase responsible for brasilane biosynthesis in Trichoderma spp. 9,10 These reports facilitated the search for the underlying biosynthetic gene clusters in the Hypoxylaceae which led us to investigate the participating tailoring enzymes.…”

“…Recently, two independent studies found and characterized the terpene cyclases (TaTC6, Tvi09626) responsible for brasilane backbone assembly in Trichoderma spp. 9,10 Using BLASTp homology searches with Tvi09626 as a template, we found a candidate biosynthetic gene cluster (BGC, bra) in the A. truncatum genome containing five genes termed braA-E (Scheme 1). BraA was identified as a terpene cyclase showing 70.9% similarity to Tvi09626, while BraB was annotated as a putative O-glycosyltransferase (O-GT) with homology to the O-GT PaGT involved in fusicoccin biosynthesis in Diaporthe (Phomopsis) amygdali.…”

Molecular methods unravel the biosynthetic potential of Trichoderma species

“…47,52 Terpenes are considered the most abundant and chemically diverse class of natural products, with an estimated number of more than 80 000 different compounds. [53][54][55] These highly diverse natural products are derived from the cyclization of polyprenyl diphosphates such as geranyl diphosphate (GPP), farnesyl diphosphate (FPP), geranylgeranyl diphosphate (GGPP) and geranylfarnesyl diphosphate (GFPP) through the action of terpene cyclases (TC). [53][54][55][56] Several terpenoids have been characterized and reported from different Trichoderma spp., however only few of their responsible biosynthetic gene clusters have been experimentally characterized.…”