8ez1
Human Ornithine Aminotransferase (hOAT) co-crystallized with its inactivator 3-Amino-4-fluorocyclopentenecarboxylic Acid
Structural highlights
DiseaseOAT_HUMAN Defects in OAT are the cause of hyperornithinemia with gyrate atrophy of choroid and retina (HOGA) [MIM:258870. HOGA is a slowly progressive blinding autosomal recessive disorder.[1] [2] [3] [4] [5] [6] FunctionPublication Abstract from PubMedOrnithine aminotransferase (OAT) is overexpressed in hepatocellular carcinoma (HCC), and we previously showed that inactivation of OAT inhibits the growth of HCC. Recently, we found that (3S,4S)-3-amino-4-fluorocyclopentenecarboxylic acid (5) was a potent inactivator of gamma-aminobutyric acid aminotransferase (GABA-AT), proceeding by an enamine mechanism. Here we describe our investigations into the activity and mechanism of 5 as an inactivator of human OAT. We have found that 5 exhibits 10-fold less inactivation efficiency (k(inact)/K(I)) against hOAT than GABA-AT. A comprehensive mechanistic study was carried out to understand its inactivation mechanism with hOAT. pK(a) and electrostatic potential calculations were performed to further support the notion that the alpha,beta-unsaturated alkene of 5 is critical for enhancing acidity and nucleophilicity of the corresponding intermediates and ultimately responsible for the improved inactivation efficiency of 5 over the corresponding saturated analogue (4). Intact protein mass spectrometry and the crystal structure complex with hOAT provide evidence to conclude that 5 mainly inactivates hOAT through noncovalent interactions, and that, unlike with GABA-AT, covalent binding with hOAT is a minor component of the total inhibition which is unique relative to other monofluoro-substituted derivatives. Furthermore, based on the results of transient-state measurements and free energy calculations, it is suggested that the alpha,beta-unsaturated carboxylate group of PLP-bound 5 may be directly involved in the inactivation cascade by forming an enolate intermediate. Overall, compound 5 exhibits unusual structural conversions which are catalyzed by specific residues within hOAT, ultimately leading to an enamine mechanism-based inactivation of hOAT through noncovalent interactions and covalent modification. Structural and Mechanistic Basis for the Inactivation of Human Ornithine Aminotransferase by (3S,4S)-3-Amino-4-fluorocyclopentenecarboxylic Acid.,Shen S, Butrin A, Beaupre BA, Ferreira GM, Doubleday PF, Grass DH, Zhu W, Kelleher NL, Moran GR, Liu D, Silverman RB Molecules. 2023 Jan 23;28(3):1133. doi: 10.3390/molecules28031133. PMID:36770800[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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