Dimeric and tetrameric forms of enoyl-acyl carrier protein reductase from Bacillus cereus

► Enoyl-[acyl carrier protein] reductase is an essential enzyme in type II fatty-acid synthesis, and FabI, FabL and FabK have been reported to carry out the reaction. ► Bacillus cereus has two ENRs, FabI and FabL. Crystal structures of the later in the apo form and in complex with NADP + and an indole naphthyridinone inhibitor. ► The two structures are almost identical, except for the three stretches that are disordered in the apo form. ► The three stretches disordered in the apo ENR are important in the cofactor and the inhibitor binding as well as in tetramer formation. ► The apo ENR exists as a homo-dimer both in crystal and in solution, while the ternary complex forms a homo-tetramer. Dimeric ENR is described for the first time. Enoyl-[acyl carrier protein] reductase (ENR) is an essential enzyme in type II fatty-acid synthesis that catalyzes the last step in each elongation cycle. Thus far FabI, FabL and FabK have been reported to carry out the reaction, with FabI being the most characterized. Some bacteria have more than one ENR, and Bacillus cereus has two (FabI and FabL) reported. Here, we have determined the crystal structures of the later in the apo form and in the ternary complex with NADP + and an indole naphthyridinone inhibitor. The two structures are almost identical, except for the three stretches that are disordered in the apo form. The apo form exists as a homo-dimer in both crystal and solution, while the ternary complex forms a homo-tetramer. The three stretches disordered in the apo structure are important in the cofactor and the inhibitor binding as well as in tetramer formation.