Woo-Ri Kang

Gene cloning of an efficiency oleate hydratase from Stenotrophomonas nitritireducens for polyunsaturated fatty acids and its application in the conversion of plant oils to 10‐hydroxy fatty acids

Hydroxy fatty acids are used as precursors of lactones and dicarboxylic acids, as starting materials of polymers, and as additives in coatings and paintings. Stenotrophomonas nitritireducens efficiently converts cis‐9 polyunsaturated fatty acids (PUFAs) to 10‐hydroxy fatty acids. However, gene encoding enzyme involved in this conversion has not been identified to date. We purified a putative fatty acid double‐bond hydratase from S. nitritireducens by ultrafiltration and HiPrep DEAE FF and Resource Q ion exchange chromatographies. Peptide sequences of the purified enzyme were obtained by liquid chromatography‐mass spectrometry/mass spectrometry (LC‐MS/MS) analysis. Sequence of the partial gene encoding this putative fatty acid double‐bond hydratase was determined by degenerate polymerase chain reaction (PCR) based on the peptide sequences. The remaining gene sequence was identified by rapid amplification of cDNA ends using cDNA of S. nitritireducens as a template, and the full‐length gene was cloned subsequently. The expressed enzyme was identified as an oleate hydratase by determining its kinetic parameters toward unsaturated fatty acids. S. nitritireducens oleate hydratase showed higher activity toward PUFAs compared with other available oleate hydratases. This suggested that the enzyme could be used effectively to convert plant oils to 10‐hydroxy fatty acids because these oils contained unsaturated fatty acids such as oleic acid (OA) and linoleic acid (LA) and PUFAs such as α‐linolenic acid and/or γ‐linolenic acid. The enzyme converted soybean oil and perilla seed oil hydrolyzates containing 10 mM total unsaturated fatty acids, including OA, LA, and ALA, to 8.87 and 8.70 mM total 10‐hydroxy fatty acids, respectively, in 240 min. To our knowledge, this is the first study on the biotechnological conversion of PUFA‐containing oils to hydroxy fatty acids. Biotechnol. Bioeng. 2017;114: 74–82.

Comparison of Biochemical Properties of the Original and Newly Identified Oleate Hydratases from Stenotrophomonas maltophilia

ABSTRACT Oleate hydratases (OhyAs) catalyze the conversion of unsaturated fatty acids to 10-hydroxy fatty acids, which are used as precursors of important industrial compounds, including lactones and ω-hydroxycarboxylic and α,ω-dicarboxylic acids. The genes encoding OhyA and a putative fatty acid hydratase in Stenotrophomonas maltophilia were identified by genomic analysis. The putative fatty acid hydratase was purified and identified as an oleate hydratase (OhyA2) based on its substrate specificity. The activity of OhyA2 as a holoenzyme was not affected by adding cofactors, whereas the activity of the original oleate hydratase (OhyA1) showed an increase. Thus, all characterized OhyAs were categorized as either OhyA1 or OhyA2 based on the activities of holoenzymes upon adding cofactors, which were determined by the type of the fourth conserved amino acid of flavin adenine dinucleotide (FAD)-binding motif. The hydration activities of S. maltophilia OhyA2 toward unsaturated fatty acids, including oleic acid, palmitoleic acid, linoleic acid, α-linolenic acid, and γ-linolenic acid, were greater than those of OhyA1. Moreover, the specific activity of S. maltophilia OhyA2 toward unsaturated fatty acids, with the exception of γ-linolenic acid, was the highest among all reported OhyAs. IMPORTANCE All characterized OhyAs were categorized as OhyA1s or OhyA2s based on the different properties of the reported and newly identified holo-OhyAs in S. maltophilia upon the addition of cofactors. OhyA2s showed higher activities toward polyunsaturated fatty acids (PUFAs), including linoleic acid, α-linolenic acid, and γ-linolenic acid, than those of OhyA1s. This suggests that OhyA2s can be used more effectively to convert plant oils to 10-hydroxy fatty acids because plant oils contain not only oleic acid but also PUFAs. The hydration activity of the newly identified OhyA2 from S. maltophilia toward oleic acid was the highest among the activity levels reported so far. Therefore, this enzyme is an efficient biocatalyst for the conversion of plant oils to 10-hydroxy fatty acids, which can be further converted to important industrial materials.

Molecular characterization of Penicillium oxalicum 6R,8R-linoleate diol synthase with new regiospecificity

Diol synthase-derived metabolites are involved in the sexual and asexual life cycles of fungi. A putative diol synthase from Penicillium oxalicum was found to convert palmitoleic acid (16:1n-7), oleic acid (18:1n-9), linoleic acid (18:2n-6), and α-linolenic acid (18:3n-3) to 6S,8R-dihydroxy-9(Z)-hexadecenoic acid, 6R,8R-dihydroxy-9(Z)-octadecenoic acid, 6R,8R-dihydroxy-9,12(Z,Z)-octadecadienoic acid, and 6S,8R-dihydroxy-9,12,15(Z,Z,Z)-octadecatrienoic acid, respectively, which were identified by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and nuclear magnetic resonance (NMR) spectroscopy analyses. The specific activity and catalytic efficiency of P. oxalicum 6,8-diol synthase were the highest for 18:2n-6, indicating that the enzyme is a 6R,8R-linoleate diol synthase (6R,8R-LDS) with new regiospecificity. This is the first report of a 6R,8R-LDS. LDS is a fusion protein consisting of a dioxygenase domain at the N-terminus and a cytochrome P450/hydroperoxide isomerase (P450/HPI) domain at the C-terminus. The putative active-site residues in the C-terminal domain of P. oxalicum 6R,8R-LDS were proposed based on a substrate-docking homology model. The results of the site-directed mutagenesis within C-terminal P450 domain suggested that Asn886, Arg707, and Arg934, are catalytic importance and belong to the catalytic groove. Phe794 and Gln889 were found to be involved in the regiospecific rearrangement of hydroperoxide, while the F794E and Q889A variants of P. oxalicum 6,8-LDS acted as 7,8- and 8,11-LDSs, respectively. All these mutations critically affected the HPI activity of P. oxalicum 6R,8R-LDS.

Complete genome sequence of Stenotrophomonas sp. KACC 91585, an efficient bacterium for unsaturated fatty acid hydration

Hydroxy fatty acids (HFAs) such as 10-hydroxystearic acid (10-HSA) and 10-hydroxy-12(Z)-octadecenoic acid (10-HOD), which are similar to ricinoleic acid, are important starting materials and intermediates for the industrial manufacture of many commodities. Stenotrophomonas sp. KACC 91585, which was isolated from lake sediment, is an efficient bacterium for unsaturated fatty acid hydration that produces 10-HSA and 10-HOD from oleic acid and linoleic acid, respectively, with high conversion rates. The complete genome of this strain is 4,541,729bp with 63.83% GC content and devoid of plasmids. Sets of genes involved in the fatty acid biosynthesis and modification as well as modified lipids were identified in the genome, and these genes were concerned with HFA production. This genome sequence provides molecular information and elucidation for HFA production, and will be used as an efficient biocatalyst source for the biotechnological production of HFA.