Omega-3 fatty acids are oxygenated at the n-7 carbon by the lipoxygenase domain of a fusion protein in the cyanobacterium Acaryochloris marina

Abstract

Lipoxygenases (LOX) are found in most organisms that contain polyunsaturated fatty acids, usually existing as individual genes although occasionally encoded as a fusion protein with a catalase-related hemoprotein. Such a fusion protein occurs in the cyanobacterium Acaryochloris marina and herein we report the novel catalytic activity of its LOX domain. The full-length protein and the C-terminal LOX domain were expressed in Escherichia coli, and the catalytic activities characterized by UV, HPLC, GC-MS, and CD. All omega-3 polyunsaturates were oxygenated by the LOX domain at the n-7 position and with R stereospecificity: α-linolenic and the most abundant fatty acid in A. marina, stearidonic acid (C18.4ω3), are converted to the corresponding 12R-hydroperoxides, eicosapentaenoic acid to its 14R-hydroperoxide, and docosahexaenoic acid to its 16R-hydroperoxide. Omega-6 polyunsaturates were oxygenated at the n-10 position, forming 9R-hydroperoxyoctadecadienoic acid from linoleic acid and 11R-hydroperoxy-eicosatetraenoic acid from arachidonic acid. The metabolic transformation of stearidonic acid by the full-length fusion protein entails its 12R oxygenation with subsequent conversion by the catalase-related domain to a novel allene epoxide, a likely precursor of cyclopentenone fatty acids or other signaling molecules (Gao et al, J. Biol. Chem. 284:22087-98, 2009). Although omega-3 fatty acids and lipoxygenases are of widespread occurrence, this appears to be the first description of a LOX-catalyzed oxygenation that specifically utilizes the terminal pentadiene of omega-3 fatty acids.

Linolenate 9R‐Dioxygenase and Allene Oxide Synthase Activities of Lasiodiplodia theobromae

“…The oxidation at the n-7 position is not a common feature of LOXs, but was recently reported by the LOX domain of a fusion protein of a cyanobacterium [33]. Oxygenation by 9R-DOX and Mn-LOX differ with regard to regiochemical and stereochemical specificity, but both enzymes catalyze suprafacial hydrogen abstraction and oxygenation [34], as outlined in Fig.…”

Steric analysis of epoxyalcohol and trihydroxy derivatives of 9-hydroperoxy-linoleic acid from hematin and enzymatic synthesis

“…C9 oxygenation in plants is catalyzed by 9-lipoxygenases (9-LOX), well-represented among the LOX genes (Feussner and Wasternack, 2002). Linoleate 9-lipoxygenases are also known in prokaryotes (Andreou et al, 2008; Gao et al, 2010; Zheng et al, 2008), and are a catalytic activity of arachidonate 12 R -LOX in higher animals (Meruvu et al, 2005; Siebert et al, 2001; Zheng et al, 2011). Among the many possible transformations of the resulting 9-hydroperoxy-octadecenoic acid (9-HPODE), in keeping with other fatty acid hydroperoxides are rearrangements to epoxy-hydroxy derivatives (fatty acid epoxyalcohols), with subsequent hydrolysis producing a collection of trihydroxy-octadecenoates.…”

A Bisallylic Mini-lipoxygenase from Cyanobacterium Cyanothece sp. That Has an Iron as Cofactor

“…These enzymes are significantly smaller than the described animal and plant LOXs and a number of them have so far been identified in cyanobacteria (35,(42)(43)(44)(45). Alignment of the predicted amino acid sequence of CspLOX2 with that of Mn-LOX shows conserved features, e.g.…”