Structure of Methylobacterium extorquens malyl-CoA lyase: CoA-substrate binding correlates with domain shift

Malyl-CoA lyase (MCL) is an Mg²⁺-dependent enzyme that catalyzes the reversible cleavage of (2S)-4-malyl-CoA to yield acetyl-CoA and glyoxylate. MCL enzymes, which are found in a variety of bacteria, are members of the citrate lyase-like family and are involved in the assimilation of one- and two-carbon compounds. Here, the 1.56 Å resolution X-ray crystal structure of MCL from Methylobacterium extorquens AM1 with bound Mg²⁺ is presented. Structural alignment with the closely related Rhodobacter sphaeroides malyl-CoA lyase complexed with Mg²⁺, oxalate and CoA allows a detailed analysis of the domain motion of the enzyme caused by substrate binding. Alignment of the structures shows that a simple hinge motion centered on the conserved residues Phe268 and Thr269 moves the C-terminal domain by about 30° relative to the rest of the molecule. This domain motion positions a conserved aspartate residue located in the C-terminal domain in the active site of the adjacent monomer, which may serve as a general acid/base in the catalytic mechanism.