Fatty Acid Origin of Insect Pheromones.

Pheromones are utilized to a great extent in insects. Many of these pheromones are biosynthesized through a pathway involving fatty acids. This chapter will provide examples where the biosynthetic pathways of fatty acid-derived pheromones have been studied in detail. These include pheromones from Lepidoptera, Coleoptera, and Hymenoptera. Many species of Lepidoptera utilize fatty acids as precursors to pheromones with a functional group that include aldehydes, alcohols, and acetate esters. In addition, the biosynthesis of hydrocarbons will be briefly examined because many insects utilize hydrocarbons or modified hydrocarbons as pheromones.

In vivo studies in the 1960s determined that labeled acetate was readily incorporated into insect cuticular lipids, especially hydrocarbons (Vroman et al. , 1965; Lamb and Monroe, 1968; Nelson, 1969), establishing the de novo synthesis of insect hydrocarbons. Later studies with specific radio-labeled precursors and careful analysis of metabolic products determined the biosynthetic pathways for the most common components. In vivo experiments with 13 C-labeled precursors extended and confirmed the conclusions based on radiochemical data. In vitro studies using microsomal preparations examined the elongation of fatty acyl-CoAs and the conversion of fatty acyl-CoAs to hydrocarbons. The mechanism of how long-chain fatty acyl-CoAs are converted to hydrocarbons has been controversial, and only recently have studies using the powerful techniques of molecular biology been applied to gaining a more complete understanding of the biosynthesis and regulation of insect hydrocarbons (Wicker-Thomas and Chertemps, Chapter 4, this book). The biosynthesis of hydrocarbons has been studied in relatively few insects, including the dipterans Musca domestica (Blomquist, 2003) and Drosophila melanogaster (Jallon and Wicker-Thomas, 2003), and considerable work has been done on cockroaches Periplaneta americana and Blattella germanica , the termite Zootermopsis angusticollis and several other insects (Nelson and Blomquist, 1995; Howard and Blomquist, 2005). Work has been done with the cabbage looper, Trichoplusia ni (Dwyer et al. , 1986; de Renobales et al. , 1988), southern armyworm Spodoptera eridania (Guo and Blomquist, 1991) and in cockroaches (Young and Schal, 1997) on the timing of hydrocarbon synthesis and its deposition on the insect cuticle. This chapter will concentrate on the biosynthesis of long-chain cuticular hydrocarbons.

Glycerophosphoethanolamine (GPEtn) and glycerophosphoserine (GPSer) lipids were reacted with a multiplexed set of differentially isotopically enriched N-methylpiperazine acetic acid N-hydroxysuccinimide ester reagents, which place isobaric mass labels at a primary amino group. The resulting derivatized aminophospholipids were isobaric and chromatographically indistinguishable but yielded positive reporter ions (m/z 114 or 117) after collisional activation that could be used to identify and quantify individual members of the multiplex set. The chromatographic and mass spectrometric response of N-methylpiperazine amide-tagged aminophospholipids was probed using glycerophosphoethanolamine and glycerophosphoserine lipid standards. The [M+H]+ of each tagged aminophospholipid shifted 144 Da, and during collision-induced dissociation the major fragmentation ion was either m/z 114 or 117. This mode of detecting aminophospholipids was useful for an unbiased analysis of plasmalogen GPEtn lipids. Molecular species information on the esterified fatty acyl substituents was obtained by collisional activation of the [M-H]- ions. The isotope-tagged reagents were used to assess changes in the distribution of GPEtn lipids after exposure of liposomes made from phospholipids extracted from RAW 264.7 cells to Cu2+/H2O2 to illustrate the ability of these reagents to aid in the mass spectrometric identification of aminophospholipid changes that occur during biological stimuli.

Hydrocarbon biosynthesis in Periplaneta americana

BgFas1: A fatty acid synthase gene required for both hydrocarbon and cuticular fatty acid biosynthesis in the German cockroach, Blattella germanica (L.)

The elongation of [9,10‐3H]oleoyl‐CoA with malonyl‐CoA to form 20, 22, and 24 carbon monounsaturated fatty acids was demonstrated in housefly microsomes by radio‐GLC. These elongation reactions, which have been postulated to be involved in hydrocarbon biosynthesis, have not been previously demonstrated in insects. 2‐Octadecynoate (18:1 Δ2=) inhibited the in vivo incorporation of [1‐14C]acetate into both fatty acids and hydrocarbons in a dose‐dependent manner. At doses of 10 μg per female housefly of the alkynoic acid, the incorporation of [1‐14C]acetate into hydrocarbon was inhibited 93%, the incorporation of [9,10‐3H]oleate into hydrocarbon was inhibited 64%, and the incorporation of [1‐14C]acetate into total internal lipid was inhibited 65%. Partially purified FAS was inhibited 50% and 95% at 15 μM and 40 μM, respectively, of the alkynoic acid. These results show that 2‐octadecynoate inhibits hydrocarbon biosynthesis in the housefly by inhibiting FAS, and the in vivo data suggest that the elongation of 18:1 to longer chain fatty acids is also inhibited.

Gas chromatography and combined gas chromatography-mass spectrometry have been used to study the fatty acids and hydrocarbons of a bacterium from the Pacific Ocean, Vibrio marinus, a freshwater blue-green alga, Anacystis nidulans, and algal mat communities from the Gulf of Mexico. Both types of microorganisms (bacteria and algae) showed relatively simple hydrocarbon and fatty acid patterns, the hydrocarbons predominating in the region of C-17 and the fatty acids in the range of C-14 to C-18. The patterns of V. marinus were more comparable to those of the algal populations than to patterns reported for other bacteria. An incomplete correlation between fatty acids and hydrocarbons in both types of organisms was observed, making it difficult to accept the concept that the biosynthesis of hydrocarbons follows a simple fatty acid decarboxylation process.

The aroma of grapes is cultivar dependent and is influenced by terroir, vineyard practices, and abiotic and biotic stresses. Trincadeira is a non-aromatic variety associated with low phenolic content and high sugar and organic acid levels. This cultivar, widely used in Portuguese wines, presents high susceptibility to Botrytis cinerea. This work aimed to characterise the volatile profile of Trincadeira grapes and how it changes under infection with B. cinerea. Thirty-six volatile organic compounds were identified, from different functional groups, namely alcohols, ester acetates, fatty acid esters, fatty acids, aldehydes, and products of the lipoxygenase pathway. Both free and glycosidic volatile organic compounds were analysed by Gas Chromatography and Gas Chromatography coupled to Mass Spectrometry for component quantification and identification, respectively. A multivariance analysis showed a clear discrimination between healthy and infected grapes with 2-trans-hexenal and isoamyl-acetate among the compounds identified as negative and positive markers of infection, respectively. Ester acetates such as 2-phenylethyl acetate, isoamyl acetate, and 2-methylbutyl acetate were present in higher contents in infected samples, whereas the contents of several fatty acid esters, such as ethyl decanoate and ethyl dodecanoate, decreased. These data were integrated with quantitative PCR data regarding genes involved in volatile metabolism and showed up-regulation of a gene coding for Hydroperoxide Lyase 2 in infected grapes. Altogether, these changes in volatile metabolism indicate an impact on the grape quality and may be related to defence against B. cinerea. The presence/absence of specific compounds might be used as infection biomarkers in the assessment of Trincadeira grapes’ quality.

An initial investigation into the mechanism of hydrocarbon biosynthesis in Sarcina lutea was performed by measuring the amounts of (14)C incorporated into the hydrocarbons and fatty acids by use of a combination gas chromatograph and high-temperature gas-flow ionization apparatus. Uniformly labeled l-isoleucine-(14)C was predominantly incorporated into the anteiso-branched chains. Palmitate-16-(14)C gave evidence that a direct correlation may exist between the nonpolar end of the palmitate and the biosynthesis of hydrocarbons and carotenoids. The label from palmitate-1-(14)C was incorporated into the various hydrocarbon groups as a compound, derived from the polar end of the palmitate, consisting of more than two carbon atoms. Palmitate-16-(14)C and -1-(14)C gave no detectable evidence that transformed products were incorporated into other fatty acids. Sodium acetate-2-(14)C and uniformly labeled l-leucine-(14)C gave evidence of a nonspecific incorporation into both the aliphatic hydrocarbons and fatty acids of Sarcina lutea.

With the progress of human society, the consumption of energy materials is increasing in particularly the fossil fuels, which accounts for 84.7% of the total global consumption in 2018. Thus, excessive exploitation of fossil fuels not only brings about an increasingly serious energy crisis, but also leads to a series of environmental problems, such as the air quality deterioration and soil acidification, which are not conducive to the sustainable development of society. Since the 21st Annual Conference of the China Association for Science and Technology in 2019, “renewable synthetic fuels” has become one of the focuses of attention, and it also puts forward higher requirements for the research and development of renewable energy. About 60 years ago, many plants, insects, microorganisms and microalgae were found to metabolize hydrocarbons. In 2010, Schirmer’s groups recognized the alkane biosynthesis pathways of marine chlorobacteria, which aroused great interest in hydrocarbon biosynthesis. Recently, more proteases to catalyze the synthesis of hydrocarbons have been successively discovered, such as aldehyde deformylase (ADO, CYP4G and CER), fatty acid decarboxylase (UndA, UndB and OleT), polyketone synthase (Ols) and thiolytic enzyme complex system (OleABCD). In the past decades, many studies have been conducted to explore the biosynthesis of hydrocarbon, and useful information regarding the reaction mechanism has been obtained, including the kinetic rate constants and the crystal structures of the enzymes. In addition, on the basis of crystal structure, quantum chemistry method (QM) and molecular dynamics simulations (MD) were also used to explore the reaction mechanism of fatty acid decarboxylation. Since most enzymes involved in the hydrocarbon biosynthesis are iron-containing enzymes, which employ the Fe-coordinate dioxygen to trigger the reaction. In general, the whole reaction cycle contains the binding of substrates and dioxygen, and decarboxylation usually involves the hydrogen atom abstraction and breaking of C−C bond. During the reaction, complex electron transfer takes place among the Fe center, O2 and substrate, and many factors were found to affect the catalytic activity. According to the previous experimental and theoretical studies, different enzymes show different activity and substrate scope. In general, the catalytic efficiency is still very low for most enzymes, and thus, understanding the mechanism of these catalytic reactions is undoubtedly an important basis for engineering optimization and all applications, and can also provide ideas for the design and synthesis of biomimetic catalysts. In this paper, we review the research progress of five representative iron enzymes that catalyze the biosynthesis of aliphatic hydrocarbon, including OleT, UndA, UndB, ADO and CYP4G, and discuss the future development and application of enzyme catalysis in renewable synthetic fuels. This paper may offer some ideas and guidelines for sustainable energy supply in the future.

Waning resources, massive energy consumption, ever-deepening global warming crisis, and climate change have raised grave concerns regarding continued dependence on fossil fuels as the predominant source of energy and generated tremendous interest for developing biofuels, which are renewable. Hydrocarbon-based 'drop-in' biofuels can be a proper substitute for fossil fuels such as gasoline or jet fuel. In Nature, hydrocarbons are produced by diverse organisms such as insects, plants, bacteria, and cyanobacteria. Metalloenzymes play a crucial role in hydrocarbons biosynthesis, and the past decade has witnessed discoveries of a number of metalloenzymes catalyzing hydrocarbon biosynthesis from fatty acids and their derivatives employing unprecedented mechanisms. These discoveries elucidated the enigma related to the divergent chemistries involved in the catalytic mechanisms of these metalloenzymes. There is substantial diversity in the structure, mode of action, cofactor requirement, and substrate scope among these metalloenzymes. Detailed structural analysis along with mutational studies of some of these enzymes have contributed significantly to identifying the key amino acid residues that dictate substrate specificity and catalytic intricacy. In this Review, we discuss the metalloenzymes that catalyze fatty acid-derived hydrocarbon biosynthesis in various organisms, emphasizing the active site architecture, catalytic mechanism, cofactor requirements, and substrate specificity of these enzymes. Understanding such details is essential for successfully implementing these enzymes in emergent biofuel research through protein engineering and synthetic biology approaches.

Obese individuals are both insulin resistant and have high levels of circulating free fatty acids (FFAs). In cell culture, saturated but not unsaturated fatty acids induce endoplasmic reticulum (ER) stress. We hypothesized that chronic exposure to low dose fatty acids would significantly attenuate the acute stress response to a saturated fatty acid challenge and that unsaturated fatty acids (oleate) would be more protective than saturated fatty acids (palmitate). The ER stress response to palmitate was reduced after low dose fatty acid exposure in human hepatoma cells. Palmitate and oleate gave distinctive transcript responses, both acutely and after chronic low dose exposure. Differentially regulated pathways included lipid, cholesterol, fatty acid, and triglyceride metabolism, and IkappaB kinase and nuclear factor kappaB kinase inflammatory cascades. Oleate reduced palmitate-induced changes significantly more than low dose palmitate and completely blocked palmitate-induced phosphoinositide 3 kinase inhibitor (PIK3IP1) as well as induction of GADD45A and B. These changes are predicted to alter the PI3 kinase pathway and the pro-apoptotic p38 MAPK pathway. We recapitulated the oleate response by small interfering RNA-mediated block of PIK3IP1 stimulation with palmitate and significantly protected cells from palmitate-mediated ER stress. We show that transcriptional responses to oleate and palmitate are distinct, broad, and often discordant. We identified several potential candidates that may direct the transcriptional networks and demonstrate that PIK3IP1 partially accounts for the protective effects of oleate.

Effect of fatty acid composition on the volatile compounds of pasteurized milk during low-temperature storage

Cyanobacteria possess the unique capacity to naturally produce hydrocarbons from fatty acids. Hydrocarbon compositions of thirty-two strains of cyanobacteria were characterized to reveal novel structural features and insights into hydrocarbon biosynthesis in cyanobacteria. This investigation revealed new double bond (2- and 3-heptadecene) and methyl group positions (3-, 4- and 5-methylheptadecane) for a variety of strains. Additionally, results from this study and literature reports indicate that hydrocarbon production is a universal phenomenon in cyanobacteria. All cyanobacteria possess the capacity to produce hydrocarbons from fatty acids yet not all accomplish this through the same metabolic pathway. One pathway comprises a two-step conversion of fatty acids first to fatty aldehydes and then alkanes that involves a fatty acyl ACP reductase (FAAR) and aldehyde deformylating oxygenase (ADO). The second involves a polyketide synthase (PKS) pathway that first elongates the acyl chain followed by decarboxylation to produce a terminal alkene (olefin synthase, OLS). Sixty-one strains possessing the FAAR/ADO pathway and twelve strains possessing the OLS pathway were newly identified through bioinformatic analyses. Strains possessing the OLS pathway formed a cohesive phylogenetic clade with the exception of three Moorea strains and Leptolyngbya sp. PCC 6406 which may have acquired the OLS pathway via horizontal gene transfer. Hydrocarbon pathways were identified in one-hundred-forty-two strains of cyanobacteria over a broad phylogenetic range and there were no instances where both the FAAR/ADO and the OLS pathways were found together in the same genome, suggesting an unknown selective pressure maintains one or the other pathway, but not both.

Lipids are produced, transported, and recognized by the concerted actions of numerous enzymes, binding proteins, and receptors. A comprehensive analysis of lipid molecules, "lipidomics," in the context of genomics and proteomics is crucial to understanding cellular physiology and pathology; consequently, lipid biology has become a major research target of the postgenomic revolution and systems biology. To facilitate international communication about lipids, a comprehensive classification of lipids with a common platform that is compatible with informatics requirements has been developed to deal with the massive amounts of data that will be generated by our lipid community. As an initial step in this development, we divide lipids into eight categories (fatty acyls, glycerolipids, glycerophospholipids, sphingolipids, sterol lipids, prenol lipids, saccharolipids, and polyketides) containing distinct classes and subclasses of molecules, devise a common manner of representing the chemical structures of individual lipids and their derivatives, and provide a 12 digit identifier for each unique lipid molecule. The lipid classification scheme is chemically based and driven by the distinct hydrophobic and hydrophilic elements that compose the lipid. This structured vocabulary will facilitate the systematization of lipid biology and enable the cataloging of lipids and their properties in a way that is compatible with other macromolecular databases.