'''GLYCINAMIDE RIBONUCLEOTIDE SYNTHETASE (GAR-SYN) FROM E. COLI.'''
===GLYCINAMIDE RIBONUCLEOTIDE SYNTHETASE (GAR-SYN) FROM E. COLI.===
==Overview==
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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 SeMet 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 A resolution. GAR-syn adopts an alpha/beta 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. A search of structural databases showed that the structure of GAR-syn is similar to D-alanine:D-alanine ligase, biotin carboxylase, and glutathione synthetase, despite low sequence similarity. These four enzymes all utilize similar ATP-dependent catalytic mechanisms even though they catalyze different chemical reactions. Another ATP-binding enzyme with low sequence similarity but unknown function, synapsin Ia, was also found to share high structural similarity with GAR-syn. Interestingly, the GAR-syn N domain shows similarity to the N-terminal region of glycinamide ribonucleotide transformylase and several dinucleotide-dependent dehydrogenases. Models of ADP and GAR binding were generated based on structure and sequence homology. On the basis of these models, 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. The structure of GAR-syn allows modeling studies of possible channeling complexes with PPRP amidotransferase.
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==About this Structure==
==About this Structure==
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[[Category: Purine de novo biosynthetic pathway]]
[[Category: Purine de novo biosynthetic pathway]]
[[Category: Substrate channeling]]
[[Category: Substrate channeling]]
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Revision as of 03:00, 1 July 2008
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X-ray crystal structure of glycinamide ribonucleotide synthetase from Escherichia coli., Wang W, Kappock TJ, Stubbe J, Ealick SE, Biochemistry. 1998 Nov 10;37(45):15647-62. PMID:9843369
