Structural analysis of ExaC, an NAD⁺-dependent aldehyde dehydrogenase, from Pseudomonas aeruginosa

The opportunistic pathogen Pseudomonas aeruginosa (Pa) utilizes ethanol as an energy source, however, ethanol metabolism generates acetaldehyde, a toxic byproduct. To mitigate this toxicity, P. aeruginosa employs aldehyde dehydrogenases (ALDHs) to oxidize acetaldehyde into less harmful compounds. ExaC, an NAD⁺-dependent ALDH from P. aeruginosa (PaExaC) and a member of group X ALDHs, plays a critical role in this detoxification by oxidizing both aldehydes and hydrazones. In this study, we determined the crystal structures of PaExaC in its apo and NAD⁺ -bound forms. PaExaC functions as a homodimer, with three distinct domains: an NAD⁺ binding domain, a catalytic domain, and an oligomerization domain. Structural analyses revealed that PaExaC's substrate entry channel (SEC) is optimized for size-selective aldehyde metabolism, with Leu120, Tyr462, and Thr302. Comparative structural and docking analyses with other ALDHs further validated PaExaC's preference for small aliphatic aldehydes and hydrazones. These findings highlight PaExaC's role in aldehyde detoxification, facilitating P. aeruginosa survival in diverse environments, and provide structural insights for developing targeted inhibitors to help treat infections.