6hx7
Crystal structure of human R180T variant of ORNITHINE AMINOTRANSFERASE at 1.8 Angstrom
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 PubMedAmong the over 50 gyrate atrophy-causing mutations of ornithine delta-aminotransferase (OAT), the R180T involves an active site residue located at the dimer interface, which in the crystal structure of OAT complexed with 5-fluoromethylornithine engages a salt bridge with the alpha-carboxylate of the substrate analogue. Starting from the previous finding that no transaminase activity was detected in CHO-K1 cells expressing the R180T variant, here we try to shed light at the protein level on the structural and/or functional defects of the R180T variant. To this aim, the variant has been cloned, expressed, purified and characterized by a combination of biochemical and structural studies. Although the R180T variant shares a similar overall conformation with the wild-type, its crystal structure solved at 1.8 A reveals slight structural alterations at the active site and at the dimeric interface. These changes are consistent with the spectroscopic and kinetic results, indicating that the variant, as compared with the wild-type OAT, shows (a) an increased Km value for l-ornithine (l-Orn), (b) an altered pyridoxal 5'-phosphate binding mode and affinity and (c) an increased thermostability. In addition, the R180T mutant exhibits a remarkable loss of catalytic activity and is endowed with the ability to catalyse not only the delta-transamination but also, albeit to a lesser extent, the alpha-transamination of l-Orn. Overall, these data indicate that the slight structural changes caused by the R180T mutation, preventing a proper collocation of l-Orn at the active site of OAT, are responsible for the notable reduction of the catalytic efficiency. ENZYMES: Ornithine aminotransferase EC 2.6.1.13. DATABASES: 6HX7.pdb. R180T variant of delta-ornithine aminotransferase associated with gyrate atrophy: biochemical, computational, X-ray and NMR studies provide insight into its catalytic features.,Montioli R, Paiardini A, Giardina G, Zanzoni S, Cutruzzola F, Cellini B, Borri Voltattorni C FEBS J. 2019 Apr 8. doi: 10.1111/febs.14843. PMID:30957963[7] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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