Steve Ealick's Research Group
Glycinamide Ribonucleotide Synthetase from Escherichia coli
PDB file: 1GSO
Glycinamide ribonucleotide synthetase (GAR-syn) catalyzes the second step of the de novo purine biosynthetic pathway; the conversion of phosphoribosylamine, glycine, and ATP to glycinamide ribonucleotide (GAR), ADP, and Pi. GAR-syn containing an N-terminal polyhistidine tag was expressed as the selenomethionyl incorporated protein for crystallographic studies. In addition, the protein as isolated contains a Pro294Leu mutation. This protein was crystallized, and the structure solved using multiple-wavelength anomalous diffraction (MAD) phase determination and refined to 1.6 Å resolution.
GAR-syn adopts an α/β structure that consists of four domains labeled N, A, B, and C. The N, A, and C domains are clustered to form a large central core structure whereas the smaller B domain is extended outward. Two hinge regions, which might readily facilitate interdomain movement, connect the B domain and the main core.
The active site lies in a cleft between the large domain and the extended B domain. Most of the residues that facilitate ATP binding belong to the A or B domains. The N and C domains appear to be largely responsible for substrate specificity. Click here for a schematic representation of the active site, with MgADp binding based on DDLigase. Thicker bonds show the ADP, while thinner structures represent protein active site residues. Dashed lines show possible hydrogen bonds. The two magnesium ions are labeled Mg1 and Mg2.
Wang W, Kappock TJ, Stubbe J, and Ealick SE. X-ray Crystal Structure of Glycinamide Ribonucleotide Synthetase from Escherichia coli. Biochemistry 37:15647-15662 (1998).
Weaver TM, Wang W and Ealick SE. Purification, Crystallization and Preliminary X-ray Diffraction Data from Selenomethionine Glycinamide Ribonucleotide Synthetase. Acta Crystallogr. D 5: 518-521 (1999).