Structural and biochemical basis of methylmalonate semialdehyde dehydrogenase ALDH6A1

ALDH6A1, a member of the ALDH family, plays a crucial role in the catabolic pathways of valine and thymine. Dysregulation of ALDH6A1 expression has been linked to a variety of diseases. Methylmalonate semialdehyde dehydrogenase deficiency (MMSDH deficiency), an autosomal recessive disorder, arises from mutations in the ALDH6A1 gene. Additionally, ALDH6A1 has emerged as a biomarker for several types of severe cancer. Despite its significance, the structural and biochemical mechanisms of ALDH6A1 remain poorly explored. The apo form of ALDH6A1 was solved by cryo-electron microscopy. Enzyme activity assay and thermal stability assays were conducted to elucidate the biochemical properties of ALDH6A1 and to find an agonist of ALDH6A1, Alda-1. The binding pattern of ALDH6A1 and nicotinamide adenine dinucleotide (NAD+) was explored by molecular docking. This study presents, for the first time, a structural analysis of ALDH6A1 in its apo form at a resolution of 2.75 Å, uncovering a tetrameric architecture with tightly interacting monomers. Our findings indicate that Alda-1, an agonist of ALDH2, enhances ALDH6A1 activity as well. Moreover, ALDH6A1, compared with ALDH2, exhibits a unique binding model with NAD+. Our results shed light on the structural aspects of ALDH6A1 and provide valuable insights into its catalytic mechanism. The precise determination of the ALDH6A1 structure holds promise for the development of targeted therapies aimed at restoring ALDH6A1 activity, thus providing potential value for individuals affected by related diseases.