Three-dimensional structure of human gamma -glutamyl hydrolase. A class I glatamine amidotransferase adapted for a complex substate.
gamma-Glutamyl hydrolase catalyzes the cleavage of the gamma-glutamyl chain of folylpoly-gamma-glutamyl substrates and is a central enzyme in folyl and antifolyl poly-gamma-glutamate metabolism. The crystal structure of human gamma-glutamyl hydrolase, determined at 1.6-A resolution, reveals that the protein is a homodimer. The overall structure of human gamma-glutamyl hydrolase contains 11 alpha-helices and 14 beta-strands, with a fold in which a central eight-stranded beta-sheet is sandwiched by three and five alpha-helices on each side. The topology is very similar to that of the class I glutamine amidotransferase domains, with the only major differences consisting of extensions in four loops and at the C terminus. These insertions are important for defining the substrate binding cleft and/or the dimer interface. Two sequence motifs are found in common between human gamma-glutamyl hydrolase and the class I glutamine amidotransferase family and include the catalytically essential residues, Cys-110 and His-220. These residues are located in the center of a large l-shaped cleft that is closed at one end and open at the other. Several conserved residues, including Glu-114, His-171, Gln-218, and Lys-223, may be important for substrate binding. Modeling of a methotrexate thioester intermediate, based on the corresponding complex of the glutamate thioester intermediate of Escherichia coli carbamoyl-phosphate synthetase, indicates that the substrate binds in an orientation with the pteroyl group toward the open end of the cleft.
Li
Hongmin
H
Division of Molecular Medicine, Wadsworth Center, Albany, New York 12201-0509, USA.
Ryan
Thomas J
TJ
Chave
Karen J
KJ
Van Roey
Patrick
P
D000595:Amino Acid Sequence; D002384:Catalysis; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D011487:Protein Conformation; D011623:gamma-Glutamyl Hydrolase / Q000737:chemistry*
D011623:gamma-Glutamyl Hydrolase