Discovery and Molecular Characterization of a Novel 9<i>S</i>-Lipoxygenase from <i>Enhygromyxa salina</i> for Fatty Acid Biotransformations

Iron-dependent lipoxygenases (LOXs) are involved in the synthesis of oxylipins from polyunsaturated fatty acids. However, they are usually difficult to overexpress in functional form in microbial cell factories. Moreover, 9-LOXs, generating 9-hydroperoxy fatty acids from C18 polyunsaturated fatty acids, have rarely been found from microbial sources. Here, we discovered a novel 9<i>S</i>-LOX in the marine myxobacterium <i>Enhygromyxa salina</i> (Es-9<i>S</i>-LOX). The recombinant enzyme produced in <i>Escherichia coli</i> exhibited remarkable activity in the dioxygenation of linoleic acid (LA, <b>1</b>), α-linolenic acid, γ-linolenic acid, and arachidonic acid specifically at the C9 position to yield the product with (<i>S</i>)-configuration at catalytic efficiency of 3.94, 1.42, 1.38, and 0.69 μM^-1·s^-1, respectively. The elucidated X-ray crystal structure of Es-9<i>S</i>-LOX reveals a long and narrow hydrophobic pocket that allows the substrate to be near the metal ion and the oxygen tunnel. The enzyme was successfully used in a chemoenzymatic reaction to generate a hydroxy fatty acid from LA. Our study thus contributes to the valorization of renewable polyunsaturated fatty acids into a variety of fatty acid derivatives, including hydroxy fatty acids.