In enzymology, a long-chain-alcohol O-fatty-acyltransferase (EC 2.3.1.75) is an enzyme that catalyzes the chemical reaction
acyl-CoA + a long-chain alcohol ⇌ {\displaystyle \rightleftharpoons } CoA + a long-chain ester
Thus, the two substrates of this enzyme are acyl-CoA and long-chain alcohol, whereas its two products are CoA and long-chain ester. This enzyme belongs to the family of transferases, specifically those acyltransferases transferring groups other than aminoacyl groups. The systematic name of this enzyme class is acyl-CoA:long-chain-alcohol O-acyltransferase. Other names in common use include wax synthase, and wax-ester synthase. In general, wax syntheses naturally accept acyl groups with carbon chain lengths of C16 or C18 and linear alcohols with carbon chain lengths ranging from C12 to C20.
Variation There are three unrelated families of wax syntheses found in many organisms including bacteria, higher plants, and animals in two known distinct forms: either just as a wax synthase enzyme, which is found predominantly in eukaryotes, or as an enzyme with dual wax synthase and acyl CoA:diacylglycerol acyltransferase function, which is often the final enzyme in the biosynthetic pathway responsible for wax ester production from fatty alcohols and fatty acyl-CoAs and is found predominantly in prokaryotes.
Prokaryotic bacteria
Acinetobacter There are frequent reports of wax esters biosynthesis in bacteria of the Acinetobacter genus. In particular, it has been shown that the Acinetobacter calcoaceticus ADP1 strain synthesizes wax esters through a bifunctional wax ester synthase/acyl-CoA: diacylglycerol acyltransferase (WS/DGAT) and that this complex can be functionally expressed in different bacterial hosts, suggesting the potential for potential microbial production of cheap jojoba-like wax esters. Furthermore, this was the first instance of bacterial WS/DGAT discovered. Finally, Acinetobacter has been considered as an alternative source for jojoba-like wax ester production, but is limited by the fact that its wax ester content never exceeds 14% of the cell's dry weight.
Rhodococcus jostii RHA1 Scientists have identified at least 14 genes in the Rhodococcus jostii RHA1 genome that encode putative wax ester synthase/acyl-CoA:diacylglycerol acyltransferase enzymes (WS/DGAT) with lengths ranging from 430 to 497 amino acid residues except for atf121 product, which was composed of 301 amino acid residues. Other bacteria that have been shown to produce wax esters through homologs for the WS/DGAT gene include Psychrobacter arcticus 273-4 and P. Cryohalolentis K5, with only one a single copy of the WS/DGAT gene, M. aquaeolei VT8, with 4 homologs for WS/DGAT and A. Baylyi, with a mixture of wax esters even though it only has one WS/DGAT coding gene. "M. tuberculosis" has also been shown to contain 15 atf genes encoding WS/DGATs. Several of these bacterial WS/DGAT enzymes have a broad substrate range despite naturally producing a small range of wax esters.
Plants
Arabidopsis thaliana Scientists have also identified, characterized, and shown the WSD1 gene in Arabidopsis thaliana to encode a bifunctional wax ester synthase/diacylglycerol acyltransferase enzyme that is embedded in the ER membrane, in which the wax synthase portion is critical to wax ester synthesis using long-chain and very-long-chain primary alcohols with C fatty acids.
Jojoba Although the first wax synthase in plants was identified in the jojoba plant, the jojoba wax synthase could not be functionally expressed in microorganisms like E. coli and S. cerevisiae.
Animals
Birds The enzyme products of genes AdWS4, TaWS4, GgWS1, GgWS2, GgWS4, and GgDGAT1 sequences have been shown to catalyze wax ester syntheses in several bird species.
Mammals Scientists have discovered cDNA encoding wax synthase in the preputial gland of mice. Furthermore, it has been shown that the wax synthase gene is located on the X chromosome, the expression of which lead to the formation of wax monoesters from straight chain, saturated, unsaturated, and polyunsaturated fatty alcohols and acids and that the formation of wax esters in mammals involves a two step biosynthetic pathway involving fatty acyl-CoA reductase and wax synthase enzymes.
Humans The enzymes produced by X-linked genes AWAT1 and AWAT2 have been shown to esterify long chain alcohols to produce wax esters and is most predominantly expressed in skin. Both enzymes have dissimilar substrate specificities: AWAT1 prefers decyl alcohol (C10) and AWAT2 prefers C16 and C18 alcohols while using oleoyl-CoA as the acyl donor. However, when using acetyl alcohol as the acyl acceptor, AWAT1 prefers saturated acyl groups, while AWAT2 shows activity with all four acyl-CoAs and performs two times better with unsaturated acyl-CoAs than with saturated ones. Along with the murine wax ester synthase, AWAT1 and AWAT2 are likely the most significant contributors in wax ester production in mammals.
Enzyme structure While the function of the molecule has been studied, its structure has yet to be identified.
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