A rotary mechanism for allostery in bacterial hybrid malic enzymes

Bacterial hybrid malic enzymes (MaeB grouping, multidomain) catalyse the transformation of malate to pyruvate, and are a major contributor to cellular reducing power and carbon flux. Distinct from other malic enzyme subtypes, the hybrid enzymes are regulated by acetyl-CoA, a molecular indicator of the metabolic state of the cell. Here we solve the structure of a MaeB protein, which reveals hybrid enzymes use the appended phosphotransacetylase (PTA) domain to form a hexameric sensor that communicates acetyl-CoA occupancy to the malic enzyme active site, 60 Å away. We demonstrate that allostery is governed by a large-scale rearrangement that rotates the catalytic subunits 70° between the two states, identifying MaeB as a new model enzyme for the study of ligand-induced conformational change. Our work provides the mechanistic basis for metabolic control of hybrid malic enzymes, and identifies inhibition-insensitive variants that may find utility in synthetic biology.