title: Expression and purification of imidazole glycerol phosphate synthase from Saccharomyces cerevisiae.
abstract: Imidazole glycerol phosphate (IGP) synthase is a glutamine amidotransferase that catalyzes the formation of IGP and 5-aminoimidazole-4-carboxamide ribonucleotide (AICAR) from N(1)-[(5'-phosphoribulosyl)formimino]-5-aminoimidazole-4-car boxamide ribonucleotide (PRFAR). This enzyme represents a junction between histidine biosynthesis and de novo purine biosynthesis. The recent characterization of the HIS7 gene in the yeast Saccharomyces cerevisiae IGP synthase established that this protein is bifunctional, representing a fusion between the N-terminal HisH domain and a C-terminal HisF domain. Catalytically active yeast HIS7 was expressed in a bacterial system under the control of T7 polymerase promoter. The recombinant enzyme was purified to homogeneity and the native molecular weight and steady-state kinetic constants were determined. The yeast enzyme is distinguished from the Escherichia coli IGP synthase in its utilization of ammonia as a substrate. HIS7 displays a higher K(m) for glutamine and a lower turnover in the ammonia-dependent IGP synthase activity. As observed with the E. coli IGP synthase, HIS7 shows a low basal level glutaminase activity that can be enhanced 1000-fold in the presence of a nucleotide substrate or analog. The purification and characterization of the S. cerevisiae enzyme will enable a more detailed investigation of the biochemical mechanisms that mediate the ammonia-transfer process. The fused structural feature of the HIS7 protein and the development of a high-level production system for the active enzyme elevate the potential for determination of its three-dimensional structure through X-ray crystallography.
authors.affiliation: Department of Medicinal Chemistry, Purdue University, West Lafayette, Indiana, 47907, USA.
authors.forename: S V
authors.initials: SV
authors.lastname: Chittur
authors.forename: Y
authors.initials: Y
authors.lastname: Chen
authors.forename: V J
authors.initials: VJ
authors.lastname: Davisson
mesh_terms: D000619:Aminohydrolases / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification* / Q000378:metabolism; D002850:Chromatography, Gel; D003001:Cloning, Molecular; D004795:Enzyme Stability; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D006639:Histidine / Q000737:chemistry; D007700:Kinetics; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics*; D014461:Ultracentrifugation
chemical_list: D011994:Recombinant Proteins; D006639:Histidine; C087227:imidazole glycerol phosphate synthase; D000619:Aminohydrolases