A role for quaternary structure in the substrate specificity of leucine dehydrogenase.
BACKGROUND
Glutamate, phenylalanine and leucine dehydrogenases catalyze the NAD(P)(+)-linked oxidative deamination of L-amino acids to the corresponding 2-oxoacids, and sequence homology between these enzymes clearly indicates the existence of an enzyme superfamily related by divergent evolution. We have undertaken structural studies on a number of members of this family in order to investigate the molecular basis of their differential amino acid specificity.


RESULTS
We have solved the X-ray structure of the leucine dehydrogenase from Bacillus sphaericus to a resolution of 2.2 A. Each subunit of this octameric enzyme contains 364 amino acids and folds into two domains, separated by a deep cleft. The nicotinamide ring of the NAD+ cofactor binds deep in this cleft, which is thought to close during the hydride transfer step of the catalytic cycle.


CONCLUSIONS
Comparison of the structure of leucine dehydrogenase with a hexameric glutamate dehydrogenase has shown that these two enzymes share a related fold and possess a similar catalytic chemistry. A mechanism for the basis of the differential amino acid specificity between these enzymes involves point mutations in the amino acid side-chain specificity pocket and subtle changes in the shape of this pocket caused by the differences in quaternary structure.
Baker
P J
PJ
Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, UK.
Turnbull
A P
AP
Sedelnikova
S E
SE
Stillman
T J
TJ
Rice
D W
DW
D000594:Amino Acid Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001407:Bacillus / Q000201:enzymology; D001665:Binding Sites; D018360:Crystallography, X-Ray; D005969:Glutamate Dehydrogenase / Q000737:chemistry; D050803:Leucine Dehydrogenase; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D012984:Software; D013379:Substrate Specificity
D000594:Amino Acid Oxidoreductases; D005969:Glutamate Dehydrogenase; D050803:Leucine Dehydrogenase