A functional role identified for conserved charged residues at theactive site entrance of lipoxygenase with double specificity

International audiencePlant lipoxygenases (LOXs) are a class of widespread dioxygenases catalyzing the hydroperoxidation offree polyunsaturated fatty acids, producing 9-hydroperoxides or 13-hydroperoxides from linoleic and-linolenic acids, and are called 9-LOX or 13-LOX, respectively. Some LOXs produce both 9- and 13-hydroperoxides. The models proposed to explain the reaction mechanism specificity fail to explain the“double specificity” character of these LOXs. In this study, we used the olive LOX1 with double specificityto investigate the implication of the charged residues R265, R268, and K283 in the orientation of thesubstrate into the active site. These residues are present in a conserved pattern around the entrance ofthe active site. Our results show that these residues are involved in the penetration of the substrate intothe active site: this positive patch could capture the carboxylate end of the substrate, and then guide itinto the active site. Due to its position on 2 helix, the residue K283 could have a more important role, itsinteraction with the substrate facilitating the motions of residues constituting the “cork of lipoxygenases”or the 2 helix, by disrupting putative hydrogen and ionic bonds