Title : Three-dimensional structure of human
gamma -glutamyl hydrolase
Abstract :
- 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