Crystal Structure of a Lipoxygenase in Complex with Substrate

Background: Lipoxygenases (LOX) catalyze the oxygenation of polyunsaturated fatty acids but generate distinct products from a common substrate. Results: We report the first structure of a LOX-substrate complex. Conclusion: The structure provides a context for understanding product specificity in enzymes that metabolize arachidonic acid. Significance: With roles in the production of potent lipid mediators, LOX are targets for drug design.Lipoxygenases (LOX) play critical roles in mammalian biology in the generation of potent lipid mediators of the inflammatory response; consequently, they are targets for the development of isoform-specific inhibitors. The regio- and stereo-specificity of the oxygenation of polyunsaturated fatty acids by the enzymes is understood in terms of the chemistry, but structural observation of the enzyme-substrate interactions is lacking. Although several LOX crystal structures are available, heretofore the rapid oxygenation of bound substrate has precluded capture of the enzyme-substrate complex, leaving a gap between chemical and structural insights. In this report, we describe the 2.0 angstrom resolution structure of 8R-LOX in complex with arachidonic acid obtained under anaerobic conditions. Subtle rearrangements, primarily in the side chains of three amino acids, allow binding of arachidonic acid in a catalytically competent conformation. Accompanying experimental work supports a model in which both substrate tethering and cavity depth contribute to positioning the appropriate carbon at the catalytic machinery.