Oxidative decarboxylation of fatty acids to terminal alkenes by a membrane-bound metalloenzyme, UndB

Biosynthetically produced alkenes are high-value molecules that can serve as ‘drop-in’ replacements for fossil fuels. Alkenes are also heavily used in the polymer, lubricant, and detergent industries. UndB is the only known membrane-bound fatty acid decarboxylase that catalyzes the conversion of fatty acids to terminal alkenes at the highest reported in vivo titers. However, the enzyme remains poorly understood and enigmatic. Here, we demonstrate the first-time purification of UndB and establish that it is an oxygen-dependent, non-heme diiron enzyme that engages conserved histidine residues at the active site. We also identify redox partners that support the activity of UndB and determine the enzyme's substrate specificity and kinetic properties. We detect CO2 as the co-product of the UndB-catalyzed reaction and provide the first evidence in favor of the hydrogen atom transfer (HAT) mechanism of the enzyme. Our findings decipher the biochemistry of an enigmatic metalloenzyme that catalyzes 1-alkene biosynthesis at the membrane interface with the highest known efficiency.