Crystal structure of the Glu-239----Gln mutant of aspartate carbamoyltransferase at 3.1-A resolution: an intermediate quaternary structure.
The structure of the unligated Glu 239----Gln mutant of Escherichia coli aspartate carbamoyltransferase (EC 2.1.3.2) has been determined to 3.1-A resolution and refined to a crystallographic residual of 0.22 in the space group P321. The unit-cell dimensions of the unligated enzyme are a = 122.3 A, c = 147.1 A. The c axis cell length is intermediate between the c axis lengths of the T (tense)(c = 142.2 A) and R (relaxed) (c = 156.2 A) state structures. Furthermore, the quaternary structure of the mutant enzyme is intermediate between the quaternary structures of the T form and the R form. The differences between the quaternary structures of the Glu-239----Gln and T-form enzymes can be described as follows: the separation between the catalytic trimers increases by approximately 1.5 A along the threefold axis, and they each rotate in opposite directions approximately 0.5 degree around the threefold axis, whereas the regulatory dimers rotate approximately 2 degrees around the twofold axes.
Gouaux
J E
JE
Gibbs Chemical Laboratory, Harvard University, Cambridge, MA 02138.
Stevens
R C
RC
Ke
H M
HM
Lipscomb
W N
WN
D001221:Aspartate Carbamoyltransferase / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology; D005971:Glutamates; D018698:Glutamic Acid; D005973:Glutamine; D046911:Macromolecular Substances; D008958:Models, Molecular; D009154:Mutation; D011487:Protein Conformation; D014961:X-Ray Diffraction
D005971:Glutamates; D046911:Macromolecular Substances; D005973:Glutamine; D018698:Glutamic Acid; D001221:Aspartate Carbamoyltransferase