The structure of bovine glutamate dehydrogenase provides insights into the mechanism of allostery.
BACKGROUND
Bovine glutamate dehydrogenase (boGDH) is a homohexameric, mitochondrial enzyme that reversibly catalyzes the oxidative deamination of L-glutamate to 2-oxoglutarate using either NADP(H) or NAD(H) with comparable efficacy. GDH represents a key enzymatic link between catabolic and biosynthetic pathways, and is therefore ubiquitous in both higher and lower organisms. Only mammalian GDH exhibits strong negative cooperativity with respect to the coenzyme, however, and is regulated by a large number of allosteric effectors.


RESULTS
The atomic structure of boGDH in complex with NADH, glutamate, and the allosteric inhibitor GTP has been determined to 2.8 A resolution. The major difference between the bacterial and bovine GDH structures is the presence of an additional 'antenna' in boGDH that protrudes from each trimer, twisting counterclockwise along the threefold axis. NADH and glutamate are clearly observed in the active site, but the contacts differ slightly from those observed in Clostridium symbiosum GDH. A second, inhibitory NADH molecule lies buried in the core of the hexamer. Finally, two GTP molecules bind near the hinge region connecting the NAD(+)- and glutamate-binding domains.


CONCLUSIONS
We propose that the antenna serves as an intersubunit communication conduit during negative cooperativity and allosteric regulation. GTP and NADH inhibit GDH by keeping the catalytic cleft in a closed conformation. In contrast, ADP probably binds to the back of the NAD(+)-binding domain and activates the enzyme by keeping the catalytic cleft open. Extensive contacts between antennae within the crystal lattice may represent hexamer interactions in solution and, perhaps, with other enzymes within the mitochondrial matrix.
Peterson
P E
PE
Department of Biological Sciences, Purdue University, West Lafayette, IN 47097, USA.
Smith
T J
TJ
D000244:Adenosine Diphosphate / Q000378:metabolism; D000494:Allosteric Regulation; D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D000641:Ammonia / Q000097:blood; D000818:Animals; D001419:Bacteria / Q000201:enzymology; D001665:Binding Sites; D002417:Cattle; D004789:Enzyme Activation; D005969:Glutamate Dehydrogenase / Q000737:chemistry* / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism; D006946:Hyperinsulinism / Q000201:enzymology; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid
D009243:NAD; D000244:Adenosine Diphosphate; D000641:Ammonia; D006160:Guanosine Triphosphate; D005969:Glutamate Dehydrogenase