title: The GTP effector site of ornithine decarboxylase from Lactobacillus 30a: kinetic and structural characterization.
abstract: A nucleotide effector site of the biodegradative form of ornithine decarboxylase from Lactobacillus 30a (OrnDC L30a) has been identified. OrnDC L30a activity at pH 8.0, where the enzyme is normally inactive, is stimulated by GTP and dGTP and to a lesser extent by GDP but not by ATP, CTP, or UTP. The pH profile indicates that activation by GTP is reflected by an increase in kcat/KM,orn (above pH 6.8), while Vmax remains constant over the pH range 4.0-9. 0. Scatchard plot analysis shows that GTP binds to OrnDC L30a at both pH 5.8 (KD = 0.11 microM) and pH 8.0 (KD = 1.6 microM), but unexpectedly, half-site binding is observed at the higher pH. The OrnDC L30a dodecamer dissociates into dimers at high pH in the presence or absence of GTP. The GTP binding site was located in difference electron density maps using low-resolution X-ray data. This represents a new type of GTP binding site. A model explaining the activation of OrnDC L30a by GTP is presented.
authors.affiliation: Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.
authors.forename: M A
authors.initials: MA
authors.lastname: Oliveira
authors.forename: D
authors.initials: D
authors.lastname: Carroll
authors.forename: L
authors.initials: L
authors.lastname: Davidson
authors.forename: C
authors.initials: C
authors.lastname: Momany
authors.forename: M L
authors.initials: ML
authors.lastname: Hackert
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D001665:Binding Sites; D002850:Chromatography, Gel; D019281:Dimerization; D004789:Enzyme Activation / Q000187:drug effects; D006160:Guanosine Triphosphate / Q000378:metabolism* / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D007778:Lactobacillus / Q000201:enzymology*; D008958:Models, Molecular; D009711:Nucleotides / Q000494:pharmacology; D009955:Ornithine Decarboxylase / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary
chemical_list: D001426:Bacterial Proteins; D009711:Nucleotides; D006160:Guanosine Triphosphate; D009955:Ornithine Decarboxylase