title: Studies of asymmetry in the three-dimensional structure of lobster D-glyceraldehyde-3-phosphate dehydrogenase.
abstract: An improved electron density map of lobster holo-D-glyceraldehyde-3-phosphate dehydrogenase has been computed to 2.9 A resolution based on two heavy atom isomorphous derivatives. This has been averaged only over the Q molecular 2-fold axis, which is known to be exact in the human holoenzyme. The map showed possible asymmetry between the subunits in which the active centers are closely related across the R axis (that is, between the red and green or between the yellow and blue subunits). A difference map between the electron density of citrate and sulfate-soaked crystals gave further evidence for possible asymmetry. The major differences of electron density between R axis-related subunits appear around the active center and suggest the following interpretations. 1. The conformation of the adenine about the glycosidic bond is the more frequently observed anti with a C-2' endo conformation for the ribose ring in the red and yellow subunits, but is probably syn with a C-3' endo conformation in the green and blue subunits.2. The adenine ribose has its 3'-hydroxyl group hydrogen-bonded to a main chain carbonyl group in the red and yellow subunits but not in the green and blue subunits, as a consequence of the differing ribose conformations. 3. Cysteine-149 is more closely associated with histidine-176 in the green and blue subunits, and appears nearer the nicotinamide in the red and yellow subunits.
mesh_terms: D000595:Amino Acid Sequence; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D001665:Binding Sites; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases; D008958:Models, Molecular; D009536:Niacinamide / Q000032:analysis; D011485:Protein Binding; D011487:Protein Conformation; D014961:X-Ray Diffraction
chemical_list: D000596:Amino Acids; D009536:Niacinamide; D005987:Glyceraldehyde-3-Phosphate Dehydrogenases