title: X-ray structure and characterization of carbamate kinase from the human parasite Giardia lamblia.
abstract: Carbamate kinase catalyzes the reversible conversion of carbamoyl phosphate and ADP to ATP and ammonium carbamate, which is hydrolyzed to ammonia and carbonate. The three-dimensional structure of carbamate kinase from the human parasite Giardia lamblia (glCK) has been determined at 3 A resolution. The crystals belonged to the monoclinic space group P2(1), with unit-cell parameters a = 69.77, b = 85.41, c = 102.1 A, beta = 106.8 degrees . The structure was refined to a final R factor of 0.227. The essentiality of glCK together with its absence in humans makes the enzyme an attractive candidate for anti-Giardia drug development. Steady-state kinetic rate constants have been determined. The k(cat) for ATP formation is 319 +/- 9 s(-1). The K(m) values for carbamoyl phosphate and ADP are 85 +/- 6 and 70 +/- 5 microM, respectively. The structure suggests that three invariant lysine residues (Lys131, Lys216 and Lys278) may be involved in the binding of substrates and phosphoryl transfer. The structure of glCK reveals that a glycerol molecule binds in the likely carbamoyl phosphate-binding site.
authors.affiliation: W. M. Keck Laboratory for Structural Biology, Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland, USA.
authors.forename: Andrey
authors.initials: A
authors.lastname: Galkin
authors.forename: Liudmila
authors.initials: L
authors.lastname: Kulakova
authors.forename: Rui
authors.initials: R
authors.lastname: Wu
authors.forename: Theodore E
authors.initials: TE
authors.lastname: Nash
authors.forename: Debra
authors.initials: D
authors.lastname: Dunaway-Mariano
authors.forename: Osnat
authors.initials: O
authors.lastname: Herzberg
mesh_terms: D002221:Carbamyl Phosphate / Q000737:chemistry / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D016829:Giardia lamblia / Q000201:enzymology*; D005990:Glycerol / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D017851:Phosphotransferases (Carboxyl Group Acceptor) / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism; D020836:Protein Structure, Quaternary; D040681:Structural Homology, Protein
chemical_list: D002221:Carbamyl Phosphate; D017851:Phosphotransferases (Carboxyl Group Acceptor); C019288:carbamate kinase; D005990:Glycerol
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