Fatty Acid Hydroperoxide Lyase: A Plant Cytochrome P450 Enzyme Involved in Wound Healing and Pest Resistance

Abstract

Plants continuously have to defend themselves against life-threatening events such as drought, mechanical damage, temperature stress, and potential pathogens. Nowadays, more and more similarities between the defense mechanism of plants and that of animals are being discovered. In both cases, the lipoxygenase pathway plays an important role. In plants, products of this pathway are involved in wound healing, pest resistance, and signaling, or they have antimicrobial and antifungal activity. The first step in the lipoxygenase pathway is the reaction of linoleic or linolenic acids with molecular oxygen, catalyzed by the enzyme lipoxygenase. The hydroperoxy fatty acids thus formed are highly reactive and dangerous for the plant and therefore further metabolized by other enzymes such as allene oxide synthase, hydroperoxide lyase, peroxygenase, or divinyl ether synthase. Recently, these enzymes have been characterized as a special class of cytochrome P450 enzymes. Hydroperoxide lyases cleave the lipoxygenase products, resulting in the formation of omega-oxo acids and volatile C6- and C9-aldehydes and -alcohols. These compounds are major contributors to the characteristic "fresh green" odor of fruit and vegetables. They are widely used as food flavors, for example, to restore the freshness of food after sterilization processes. The low abundance of these compounds in nature and the high demand make it necessary to synthesize them on a large scale. Lipoxygenase and hydroperoxide lyase are suitable biocatalysts for the production of "natural" food flavors. In contrast to lipoxygenase, which has been extensively studied, little is yet known about hydroperoxide lyase. Hydroperoxide lyases from different organisms have been isolated, and a few genes have been published lately. However, the structure and reaction mechanism of this enzyme are still unclear. The identification of this enzyme as a cytochrome P450 sheds new light on its structure and possible reaction mechanism, whereas recombinant expression brings a biocatalytic application into sight.

Biosynthesis of plant‐derived flavor compounds

“…Similar to LOX, HPL can be classified into two groups according to substrate specificity (Noordermeer et al, 2001). HPL is a member of the cytochrome P450 family CYP74B/C, and acts on a hydroperoxy functionality in a lipid peroxide without any co-factor.…”

Lipid metabolism in arbuscular mycorrhizal roots of Medicago truncatula

“…This enzyme family also includes allene oxide synthases (AOS, CYP74A,C) and hydroperoxide lyases (HPL, CYP74B,C) [3], enzymes that also use fatty acid hydroperoxides derived from lipoxygenase activity as substrates. In contrast to most P450-containing enzymes, proteins from the CYP74 subfamily do neither require molecular oxygen nor NADPH [6] as cosubstrates. AOS catalyze the conversion of fatty acid hydroperoxides to allene oxides which are rapidly hydrolyzed to their corresponding ketols or undergo non-enzymatic cyclization to racemic cyclopentenone derivatives.…”

“…With 9-HPODE as a substrate, the recombinant StAOS3 exhibited a pH optimum of pH 6 to 6.5. To characterize the nature of the products of the enzyme reaction of StAOS3, we used [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]-9-HPOTE as substrate. The reaction product, eluting at about 7 min, showed the same retention time in the HPLC-chromatograms as the α-ketol synthesized as control by unspecific 9/13-AOS from barley (Maucher et al, 2000).…”

“…To analyze if 9,10-EO(D/T), the reaction products of StAOS3, serve as substrates for the AOC from potato, we expressed StAOC in E. coli and determined the product specificity by calculating the ratio between α-ketol and cyclopentenone, eluting at about 10 min, in the radio-HPLC-chromatogram after incubation together with different AOS enzymes. When StAOC was incubated together with StAOS1 (CAD29735) and [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]-13-HPOTE mostly 12-OPDA was observed as product ( Figure 2b). When 13-HPODE or 9-HPO(D/T)E, respectively, were used together with StAOS1 or StAOS3 in the assay with StAOC, no AOC activity was detectable indicated by the low amount of cyclopentenones formed This is shown in Figure 2a for StAOS3 together [1][2][3][4][5][6][7][8][9][10][11][12][13][14] C]-9-HPOTE.…”

“…-oxo fatty acids [8]. HPL-products and deduced compounds are implicated as anti-microbial toxins and as signals for the regulation of growth processes and gene expression [6]. Among HPL and AOS enzymes there are isoforms which predominantly use either 13-or 9-hydroperoxides (CYP74A, B and C), or which have no strict substrate preferences (CYP74C) [3].…”