6u2x
Structure of ALDH7A1 mutant E399G complexed with NAD
Structural highlights
DiseaseAL7A1_HUMAN Pyridoxine-dependent epilepsy. The disease is caused by mutations affecting the gene represented in this entry. FunctionAL7A1_HUMAN Multifunctional enzyme mediating important protective effects. Metabolizes betaine aldehyde to betaine, an important cellular osmolyte and methyl donor. Protects cells from oxidative stress by metabolizing a number of lipid peroxidation-derived aldehydes. Involved in lysine catabolism.[1] [2] Publication Abstract from PubMedCertain loss-of-function mutations in the gene encoding the lysine catabolic enzyme aldehyde dehydrogenase 7A1 (ALDH7A1) cause pyridoxine-dependent epilepsy (PDE). Missense mutations of Glu427, especially Glu427Gln, account for ~30% of the mutated alleles in PDE patients, and thus Glu427 has been referred to as a mutation hot spot of PDE. Glu427 is invariant in the ALDH superfamily and forms ionic hydrogen bonds with the nicotinamide ribose of the NAD(+) cofactor. Here we report the first crystal structures of ALDH7A1 containing pathogenic mutations targeting Glu427. The mutant enzymes E427Q, Glu427Asp, and Glu427Gly were expressed in Escherichia coli and purified. The recombinant enzymes displayed negligible catalytic activity compared to the wild-type enzyme. The crystal structures of the mutant enzymes complexed with NAD(+) were determined to understand how the mutations impact NAD(+) binding. In the E427Q and E427G structures, the nicotinamide mononucleotide is highly flexible and lacks a defined binding pose. In E427D, the bound NAD(+) adopts a "retracted" conformation in which the nicotinamide ring is too far from the catalytic Cys residue for hydride transfer. Thus, the structures revealed a shared mechanism for loss of function: none of the variants are able to stabilize the nicotinamide of NAD(+) in the pose required for catalysis. We also show that these mutations reduce the amount of active tetrameric ALDH7A1 at the concentration of NAD(+) tested. Altogether, our results provide the three-dimensional molecular structural basis of the most common pathogenic variants of PDE and implicate strong (ionic) hydrogen bonds in the etiology of a human disease. This article is protected by copyright. All rights reserved. Structural Analysis of Pathogenic Mutations Targeting Glu427 of ALDH7A1, the Hot Spot Residue of Pyridoxine-Dependent Epilepsy.,Laciak AR, Korasick DA, Gates KS, Tanner JJ J Inherit Metab Dis. 2019 Oct 25. doi: 10.1002/jimd.12184. PMID:31652343[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. See AlsoReferences
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