A microsomal fatty acid synthetase from the integument of Blattella germanica synthesizes methyl-branched fatty acids, precursors to hydrocarbon and contact sex pheromone

The pheromone biosynthetic pathway for production of the sex pheromone disparlure, 2-methyl-7R,8S-epoxy-octadecane, was determined for the gypsy moth. Each step in the pathway was followed by using deuterium-labeled compounds that could be identified by using GC͞MS. This approach provides unequivocal determination of specific reactions in the pathway. It was shown that the alkene precursor, 2-methyl-Z7-octadecene, is most likely made in oenocyte cells associated with abdominal epidermal cells. The pathway begins with valine contributing carbons for chain initiation, including the methyl-branched carbon, followed by chain elongation to 19 carbons. The double bond is introduced with an unusual ⌬12 desaturase that utilizes a methyl-branched substrate. The resulting 18-methyl-Z12-nonadecenoate is decarboxylated to the hydrocarbon, 2-methyl-Z7-octadecene. The alkene is then transported to the pheromone gland through the hemolymph, most probably by lipophorin. At the pheromone gland, the alkene is unloaded and transformed into the epoxide disparlure for release into the environment. A chiral HPLC column was used to demonstrate that the (R,S)-stereoisomer of the epoxide, (؉)-disparlure is found in pheromone glands.

“…Hydrocarbon chain elongation is thought to occur with a microsomal fatty acid synthetase (19). The alkene would be produced by chain elongation to 19 carbons yielding 18me-19:CoA.…”

Section: Fig 2 Valine Incorporation Into the Alkene 2me-7-18:hc (A)mentioning

confidence: 99%

Sex pheromone biosynthetic pathway for disparlure in the gypsy moth, Lymantria dispar

Jurenka

Subchev

Abad

et al. 2003

“…In all cases, the absolute configuration was (R) cytochrome-P450-mediated decarbonylation result in internally branched chiral MBCHs (2,56). Although the enoyl-ACP reductase domain has yet to be isolated from insects and there have been only a few reports of microsomal FAS isolation (54,57), FAS isolated from fungal species show highly conserved NADPH binding sites and genetic homology within the enoyl reductase domain (58), suggesting that this domain may also be conserved within the Insecta. Such conservation would explain the lack of stereochemical diversity in our isolated MBCHs and the enantiospecificity in their biosynthesis.…”

Section: Discussionmentioning

confidence: 97%

“…The hydrocarbon chains are formed by microsomal 3-ketoacyl-acyl carrier protein (ACP) synthase-catalyzed Claisen condensations of malonyl-CoA substrates, with the methyl branches being introduced by insertion of a methyl malonyl-CoA into the growing hydrocarbon chain (54). The stereochemistry of the methyl branch is likely controlled by a stereoselective NADPHcatalyzed reduction of the resulting α,β-unsaturated thioester by the enoyl-ACP reductase domain of the fatty acid synthase (FAS) (Fig.…”

Section: Discussionmentioning

confidence: 99%

Isolation and determination of absolute configurations of insect-produced methyl-branched hydrocarbons

Bello¹,

McElfresh

Millar

2015

Although the effects of stereochemistry have been studied extensively for volatile insect pheromones, little is known about the effects of chirality in the nonvolatile methyl-branched hydrocarbons (MBCHs) used by many insects as contact pheromones. MBCHs generally contain one or more chiral centers and so two or more stereoisomeric forms are possible for each structure. However, it is not known whether insects biosynthesize these molecules in high stereoisomeric purity, nor is it known whether insects can distinguish the different stereoisomeric forms of MBCHs. This knowledge gap is due in part to the lack of methods for isolating individual MBCHs from the complex cuticular hydrocarbon (CHC) blends of insects, as well as the difficulty in determining the absolute configurations of the isolated MBCHs. To address these deficiencies, we report a straightforward method for the isolation of individual cuticular hydrocarbons from the complex CHC blend. The method was used to isolate 36 pure MBCHs from 20 species in nine insect orders. The absolute stereochemistries of the purified MBCHs then were determined by digital polarimetry. The absolute configurations of all of the isolated MBCHs were determined to be (R) by comparison with a library of synthesized, enantiomerically pure standards, suggesting that the biosynthetic pathways used to construct MBCHs are highly conserved within the Insecta. The development of a straightforward method for isolation of specific CHCs will enable determination of their functional roles by providing pure compounds for bioassays.T he use of chemical signals is highly developed within insects, with semiochemicals mediating a wide variety of inter-and intraspecific behaviors. Volatile pheromones, such as sex and aggregation pheromones, are the most well-known types, but insects also use nonvolatile cuticular lipids as contact pheromones (1-4). The cuticular lipids consist of a complex blend of n-and methyl-branched alkanes, alkenes, and lesser amounts of more polar compounds such as esters and alcohols. The lipid layer acts primarily as a waterproofing barrier (5), but individual lipid components have evolved secondary roles as signals that mediate a variety of behaviors and physiological changes (1, 2, 6). For example, solitary insects use cuticular hydrocarbons (CHCs) to identify the species and sex of mates (7, 8) whereas, in social insects, CHCs mediate identification of nestmates (9, 10), recognition of castes, and task allocation within the colony (11). Social insect queens also use CHCs to signal fecundity and dominance status within the colony, inhibiting development of workers into reproductives (12)(13)(14).Determining the roles of specific CHCs as signals has been hindered by three interlinked problems. First, CHCs typically consist of a large number of compounds, which can be difficult to isolate in pure form to test their bioactivities. Specifically, CHCs have very similar polarity and so are not separable by liquid chromatography on silica gel or other polar chromatographic m...

“…6). The methyl-branched alkane is formed by the insertion of methylmalonyl units derived from succinate and the carbon skeletons of isoleucine, valine, and methionine early in chain elongation (13) by a microsomal fatty acid synthetase (19). The 3,11-dimethylalkane is then selectively hydroxylated in reproductively mature females, and JH induces this process.…”

Section: Methodsmentioning

confidence: 99%

Biosynthesis and endocrine control of the production of the German cockroach sex pheromone 3,11-dimethylnonacosan-2-one.

Chase

Touhara

Prestwich

et al. 1992

The biosynthesis and endocrine regulation of sex pheromone production in the female German cockroach (Blattela germanica) were determined. Radio-TLC and radio-GLC were used to demonstrate the metabolism of 3,11-dimethylnonacosane, a major cuticular lipid component, to the corresponding alkan-2-ol and methyl ketone. [11,12-3H2J-3,11-Dimethylnonacosan-2-ol was efficiently metabolized to the methyl ketone, and radio-GLC showed that the methyl ketone product from both experiments was coeluted with a methyl ketone standard. A comparison ofthe metabolism of the labeled dimethylalkane and dimethylalkan-2-ol by age and sex showed that both males and females from day 1 through day 9 after adult emergence readily metabolized the alcohol to the corresponding methyl ketone, whereas only females of 5-9 days postemergence efficiently converted the labeled dimethylalkane to the corresponding methyl ketone. Application of the juvenile hormone analog hydroprene induced significant increases in the conversion of the labeled hydrocarbon to the methyl ketone in starved adult females as well as in females fed a protein-free diet, conditions under which endogenous juvenile hormone biosynthesis is nearly undetectable. These data show that the methyl ketone sex pheromone is formed by the hydroxylation and oxidation of the 3,11-dimethylalkane at the 2 position, show that the age-and sex-specific step in this process is the conversion of 3,11-dimethylnonacosane to 3,11-dimethylnonacosan-2-ol, and provide evidence that juvenile hormone regulates sex pheromone production in the German cockroach.