|
type |
Journal Article |
authors |
Shah, S. A.; Shen, B. W.; Brunger, A. T. |
title |
Human ornithine aminotransferase complexed with L-canaline and gabaculine: structural basis for substrate recognition |
journal |
Structure |
Activity |
2.6.1.13 |
ui |
97454792 |
year |
(1997) |
volume |
5 |
number |
8 |
pages |
1067-75. |
| |
keywords |
Aminobutyric Acids/*chemistry |
abstract |
BACKGROUND: Ornithine aminotransferase (OAT) is a 45 kDa pyridoxal-5'- phosphate (PLP)-dependent enzyme that catalyzes the conversion of L- ornithine and 2-oxoglutarate to glutamate-delta-semialdehyde and glutamic acid, respectively. In humans, loss of OAT function causes an accumulation of ornithine that results in gyrate atrophy of the choroid and retina, a disease that progressively leads to blindness. In an effort to learn more about the structural basis of this enzyme's function, we have determined the X-ray structures of OAT in complex with two enzyme-activated suicide substrates: L-canaline, an ornithine analog, and gabaculine, an irreversible inhibitor of several related aminotransferases. RESULTS: The structures of human OAT bound to the inhibitors gabaculine and L-canaline were solved to 2.3 A at 110K by difference Fourier techniques. Both inhibitors coordinate similarly in the active site, binding covalently to the PLP cofactor and causing a 20 degrees rotation in the cofactor tilt relative to the ligand-free form. Aromatic-aromatic interactions occur between the bound gabaculine molecule and active-site residues Tyr85 and Phe177, whereas Tyr55 and Arg180 provide specific contacts to the alpha-amino and carboxyl groups of L-canaline. CONCLUSIONS: The OAT-L-canaline complex structure implicates Tyr55 and Arg180 as the residues involved in coordinating with the natural substrate ornithine during normal enzyme turnover. This correlates well with two enzyme-inactivating point mutations associated with gyrate atrophy, Tyr55-->His and Arg180-->Thr. The OAT- gabaculine complex provides the first structural evidence that the potency of the inhibitor is due to energetically favourable aromatic interactions with residues in the active site. This aromatic-binding mode may be relevant to structure-based drug design efforts against other omega-aminotransferase targets, such as GABA aminotransferase. |
last changed |
2002/11/04 17:41 |
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