title: Chorismate mutase of Thermus thermophilus is a monofunctional AroH class enzyme inhibited by tyrosine.
abstract: aroG, encoding the monofunctional chorismate mutase (TtCM) of the thermophilic gram-negative bacterium Thermus thermophilus, was cloned and its gene product characterized. TtCM was purified to homogeneity on an SDS polyacrylamide gel as a His-fusion protein with a deduced molecular mass of 15.8 kDa. The enzyme belongs to the rare group of AroH-type chorismate mutases which are mainly found in gram-positive bacteria of the Bacillus/ Clostridia group and have recently also been described for gram-negative organisms. The native molecular mass is consistent with a pseudo-alpha/beta barrel enzyme that is organized as a trimer. Comparison of the enzyme's structure with that of its mesophilic counterpart from Bacillus revealed an increase in hydrophilicity on the protein's surface, greater hydrophobicity in cavities within the protein, and greater restriction of conformational freedom, features that contribute to the thermal stability of this chorismate mutase. The kinetic data show Michaelis-Menten substrate saturation with a Km of 290 microM, and a kcat/ Km value of 180 s(-1) mM(-1). TtCM was inhibited by tyrosine with a Ki =34 microM, possibly in a competitive manner.
authors.affiliation: Abteilung Molekulare Mikrobiologie und Genetik, Institut für Mikrobiologie und Genetik, Grisebachstrasse 8, 37077 Göttingen, Germany.
authors.forename: Kerstin
authors.initials: K
authors.lastname: Helmstaedt
authors.forename: Gabriele
authors.initials: G
authors.lastname: Heinrich
authors.forename: Rainer
authors.initials: R
authors.lastname: Merkl
authors.forename: Gerhard H
authors.initials: GH
authors.lastname: Braus
mesh_terms: D000595:Amino Acid Sequence; D002826:Chorismate Mutase / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D003001:Cloning, Molecular; D004269:DNA, Bacterial / Q000737:chemistry / Q000302:isolation & purification; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D005798:Genes, Bacterial; D007700:Kinetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010802:Phylogeny; D011487:Protein Conformation; D021122:Protein Subunits / Q000502:physiology; D011994:Recombinant Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D016963:Thermus thermophilus / Q000201:enzymology* / Q000235:genetics*; D014443:Tyrosine / Q000494:pharmacology*
chemical_list: D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D021122:Protein Subunits; D011994:Recombinant Proteins; D014443:Tyrosine; D002826:Chorismate Mutase