Lipoxygenases (LOXs), which are essential in eukaryotes, have no confirmed function in prokaryotes that are devoid of polyunsaturated fatty acids. The structure of a secretable LOX from Pseudomonas aeruginosa (Pa_LOX), the first available from a prokaryote, presents significant differences with respect to eukaryotic LOXs, including a cluster of helices acting as a lid to the active center. The mobility of the lid and the structural variability of the N-terminal region of Pa_LOX was confirmed by comparing 2 crystal forms. The binding pocket contains a phosphatidylethanolamine phospholipid with branches of 18 (sn-1) and 14/16 (sn-2) carbon atoms in length. Carbon atoms from the sn-1 chain approach the catalytic iron in a manner that sheds light on how the enzymatic reaction might proceed. The findings in these studies suggest that Pa_LOX has the capacity to extract and modify unsaturated phospholipids from eukaryotic membranes, allowing this LOX to play a role in the interaction of P. aeruginosa with host cells.—Garreta, A., Val-Moraes, SP, García-Fernández, Q., Montserrat Busquets, CJ, Oliver, A., Ortiz, A., Gaffney, BJ, Fita, I., Manresa, A., Carpena, X. Structure and interaction with phospholipids of a prokaryotic lipoxygenase from Pseudomonas aeruginosa.