Aldehyde dehydrogenase 7A1
Researchers using the SBC-CAT 19-ID-D and NE-CAT 24-ID-E beamlines at the APS are searching for answers as to why Aldehyde dehydrogenase 7A1 (ALDH7A1, also called antiquitin) can cause cancers and epilepsy when it mutates.
Herein we describe a structural and biochemical study of ALDH7A1 focusing on substrate recognition and conformational change. We report the first structures of the fulllength human enzyme, including the first structure of any ALDH7 family member complexed. The structures show that the C-terminus is a mobile active site element that facilitates substrate recognition.
Aldehyde dehydrogenase 7A1 (ALDH7A1) is part of lysine catabolism and catalyzes the NAD+-dependent oxidation of α-aminoadipate semialdehyde to α-aminoadipate. Herein we describe a structural study of human ALDH7A1 focused on substrate recognition. Five crystal structures and small-angle X-ray scatting data are reported, including the first crystal structure of any ALDH7 family member complexed with α-aminoadipate.
The product binds with the ε-carboxylate in the oxyanion hole, the aliphatic chain packed into an aromatic box, and the distal end of the product anchored by electrostatic interactions with five conserved residues. This binding mode resembles that of glutamate bound to the proline catabolic enzyme ALDH4A1.
Analysis of ALDH7A1 and ALDH4A1 structures suggests key interactions that underlie substrate discrimination. Structures of apo ALDH7A1 reveal dramatic conformational differences from the product complex. Product binding is associated with a 16-Å movement of the C-terminus into the active site, which stabilizes the active conformation of the aldehyde substrate anchor loop. That the C-terminus is part of the active site was hitherto unknown. Interestingly, the C-terminus and aldehyde anchor loop are disordered in a new tetragonal crystal form of the apo enzyme, implying that these parts of the enzyme are highly flexible.
Our results suggest that the active site of ALDH7A1 is disassembled when the aldehyde site is vacant, and the C-terminus is a mobile element that forms quaternary structural interactions that aid aldehyde binding. These results are relevant to the c.1512delG genetic deletion associated with pyridoxine-dependent epilepsy, which alters the C-terminus of ALDH7A1.
Min Luo and John J Tanner, “Structural Basis of Substrate Recognition by Aldehyde Dehydrogenase 7A1,” Biochemistry, Just Accepted Manuscript. DOI: 10.1021/acs.biochem.5b00754. Published Online August 11, 2015.