Characterization of a fatty acyl-CoA reductase from Marinobacter aquaeolei VT8: A bacterial enzyme catalyzing the reduction of fatty acyl-CoA to fatty alcohol

Fatty alcohols are of interest as a renewable feedstock to replace petroleum compounds used as fuels, in cosmetics, and in pharmaceuticals. One biological approach to the production of fatty alcohols involves the sequential action of two bacterial enzymes: (i) reduction of a fatty acyl-CoA to the corresponding fatty aldehyde catalyzed by a fatty acyl-CoA reductase, followed by (ii) reduction of the fatty aldehyde to the corresponding fatty alcohol catalyzed by a fatty aldehyde reductase. Here, we identify, purify, and characterize a novel bacterial enzyme from Marinobacter aquaeolei VT8 that catalyzes the reduction of fatty acyl-CoA by four electrons to the corresponding fatty alcohol, eliminating the need for a separate fatty aldehyde reductase. The enzyme is shown to reduce fatty acyl-CoAs ranging from C8:0 to C20:4 to the corresponding fatty alcohols, with the highest rate found for palmitoyl-CoA (C16:0). The dependence of the rate of reduction of palmitoyl-CoA on substrate concentration was cooperative, with an apparent K _m ∼ 4 μM, V _max ∼ 200 nmol NADP ⁺ min ^-1 (mg protein) ^-1, and n ∼ 3. The enzyme also reduced a range of fatty aldehydes with decanal having the highest activity. The substrate cis-11-hexadecenal was reduced in a cooperative manner with an apparent K _m of ∼50 μM, V _max of ∼8 μmol NADP ⁺ min ^-1 (mg protein) ^-1, and n ∼ 2.