title: Characterization, kinetics, and crystal structures of fructose-1,6-bisphosphate aldolase from the human parasite, Giardia lamblia.
abstract: Class I and class II fructose-1,6-bisphosphate aldolases (FBPA), glycolytic pathway enzymes, exhibit no amino acid sequence homology and utilize two different catalytic mechanisms. The mammalian class I FBPA employs a Schiff base mechanism, whereas the human parasitic protozoan Giardia lamblia class II FBPA is a zinc-dependent enzyme. In this study, we have explored the potential exploitation of the Giardia FBPA as a drug target. First, synthesis of FBPA was demonstrated in Giardia trophozoites by using an antibody-based fluorescence assay. Second, inhibition of FBPA gene transcription in Giardia trophozoites suggested that the enzyme is necessary for the survival of the organism under optimal laboratory growth conditions. Third, two crystal structures of FBPA in complex with the transition state analog phosphoglycolohydroxamate (PGH) show that the enzyme is homodimeric and that its active site contains a zinc ion. In one crystal form, each subunit contains PGH, which is coordinated to the zinc ion through the hydroxamic acid hydroxyl and carbonyl oxygen atoms. The second crystal form contains PGH only in one subunit and the active site of the second subunit is unoccupied. Inspection of the two states of the enzyme revealed that it undergoes a conformational transition upon ligand binding. The enzyme cleaves d-fructose-1,6-bisphosphate but not d-tagatose-1,6-bisphosphate, which is a tight binding competitive inhibitor. The essential role of the active site residue Asp-83 in catalysis was demonstrated by amino acid replacement. Determinants of catalysis and substrate recognition, derived from comparison of the G. lamblia FBPA structure with Escherichia coli FBPA and with a closely related enzyme, E. coli tagatose-1,6-bisphosphate aldolase (TBPA), are described.
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland 20850.
authors.forename: Andrey
authors.initials: A
authors.lastname: Galkin
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland 20850.
authors.forename: Liudmila
authors.initials: L
authors.lastname: Kulakova
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland 20850.
authors.forename: Eugene
authors.initials: E
authors.lastname: Melamud
authors.affiliation: Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, and.
authors.forename: Ling
authors.initials: L
authors.lastname: Li
authors.affiliation: Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, and.
authors.forename: Chun
authors.initials: C
authors.lastname: Wu
authors.affiliation: Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, and.
authors.forename: Patrick
authors.initials: P
authors.lastname: Mariano
authors.affiliation: Department of Chemistry, University of New Mexico, Albuquerque, New Mexico 87131, and.
authors.forename: Debra
authors.initials: D
authors.lastname: Dunaway-Mariano
authors.affiliation: Laboratory of Parasitic Diseases, NIAID, National Institutes of Health, Bethesda, Maryland 20892.
authors.forename: Theodore E
authors.initials: TE
authors.lastname: Nash
authors.affiliation: Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, Rockville, Maryland 20850. Electronic address: osnat@carb.nist.gov.
authors.forename: Osnat
authors.initials: O
authors.lastname: Herzberg
mesh_terms: D000818:Animals; D001665:Binding Sites; D002384:Catalysis; D018360:Crystallography, X-Ray; D004791:Enzyme Inhibitors / Q000737:chemistry / Q000627:therapeutic use; D004926:Escherichia coli / Q000201:enzymology; D005634:Fructose-Bisphosphate Aldolase / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D016829:Giardia lamblia / Q000201:enzymology*; D005873:Giardiasis / Q000188:drug therapy / Q000201:enzymology; D006801:Humans; D007700:Kinetics; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D015800:Protozoan Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry* / Q000378:metabolism; D013379:Substrate Specificity; D015032:Zinc / Q000737:chemistry / Q000378:metabolism
chemical_list: D004791:Enzyme Inhibitors; D015800:Protozoan Proteins; D005634:Fructose-Bisphosphate Aldolase; D015032:Zinc