5VWO : Ornithine aminotransferase inactivated by (1R,3S,4S)-3-amino-4-fluorocyclopentane-1-carboxylic acid (FCP)

  • Romila Mascarenhas (Contributor)
  • Hoang V. Le (Contributor)
  • Richard B Silverman (Contributor)
  • Dali Liu (Contributor)



Experimental Technique/Method:X-RAY DIFFRACTION
Release Date:2017-08-30
Deposition Date:2017-05-22
Revision Date:2017-09-20#2017-09-27#2017-10-04
Molecular Weight:135655.81
Macromolecule Type:Protein
Residue Count:1212
Atom Site Count:9658

Potent mechanism-based inactivators can be rationally designed against pyridoxal 5'-phosphate (PLP)-dependent drug targets, such as ornithine aminotransferase (OAT) or γ-aminobutyric acid aminotransferase (GABA-AT). An important challenge, however, is the lack of selectivity toward other PLP-dependent, off-target enzymes, because of similarities in mechanisms of all PLP-dependent aminotransferase reactions. On the basis of complex crystal structures, we investigate the inactivation mechanism of OAT, a hepatocellular carcinoma target, by (1R,3S,4S)-3-amino-4-fluorocyclopentane-1-carboxylic acid (FCP), a known inactivator of GABA-AT. A crystal structure of OAT and FCP showed the formation of a ternary adduct. This adduct can be rationalized as occurring via an enamine mechanism of inactivation, similar to that reported for GABA-AT. However, the crystal structure of an off-target, PLP-dependent enzyme, aspartate aminotransferase (Asp-AT), in complex with FCP, along with the results of attempted inhibition assays, suggests that FCP is not an inactivator of Asp-AT, but rather an alternate substrate. Turnover of FCP by Asp-AT is also supported by high-resolution mass spectrometry. Amid existing difficulties in achieving selectivity of inactivation among a large number of PLP-dependent enzymes, the obtained results provide evidence that a desirable selectivity could be achieved, taking advantage of subtle structural and mechanistic differences between a drug-target enzyme and an off-target enzyme, despite their largely similar substrate binding sites and catalytic mechanisms.
Date made available2017

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