title: The influence of ATP on the association and unfolding of the tyrosine repressor ligand response domain of Haemophilus influenzae.
abstract: The secondary structure of the ligand response domain of the Haemophilus influenzae tyrosine repressor, TyrR(lrd), was investigated using CD spectroscopy which revealed 42.5% alpha-helix, 17.6% beta-sheet, and 39.9% loops. Quaternary structure analysis by fluorescence anisotropy showed that TyrR(lrd) is monomeric at a concentration of 100 nM to 2 microM but that the protein readily dimerizes in the presence of its natural ligand ATP. Equilibrium unfolding studies of TyrR(lrd) using guanidinium hydrochloride suggested a two-state model with no detectable stable intermediates. The unfolding transition monitored by CD spectroscopy was responsive to tyrosine and ATP resulting in a shift to higher denaturant concentrations in the presence of these ligands. Differential scanning calorimetry yielded melting temperatures, T(m), of 51.15 and 58.07 degrees C for the unliganded and for the ATP-liganded protein, respectively. ATP is thus proposed to be a major structural cofactor for the molecular architecture of TyrR(lrd).
authors.affiliation: Institute of Pharmaceutical Chemistry, University of Graz, Universitätsplatz 1, Graz, A-8010, Austria.
authors.forename: S
authors.initials: S
authors.lastname: Kristl
authors.forename: S
authors.initials: S
authors.lastname: Zhao
authors.forename: S F
authors.initials: SF
authors.lastname: Falsone
authors.forename: R L
authors.initials: RL
authors.lastname: Somerville
authors.forename: A J
authors.initials: AJ
authors.lastname: Kungl
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism*; D001665:Binding Sites; D002152:Calorimetry, Differential Scanning; D002942:Circular Dichroism; D019281:Dimerization; D029968:Escherichia coli Proteins; D005454:Fluorescence Polarization; D019791:Guanidine; D006193:Haemophilus influenzae / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D011489:Protein Denaturation; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012097:Repressor Proteins / Q000737:chemistry* / Q000378:metabolism*; D013696:Temperature; D013816:Thermodynamics; D014157:Transcription Factors / Q000737:chemistry / Q000378:metabolism
chemical_list: D029968:Escherichia coli Proteins; D008024:Ligands; D011994:Recombinant Proteins; D012097:Repressor Proteins; D014157:Transcription Factors; C069256:TyrR protein, E coli; D000255:Adenosine Triphosphate; D019791:Guanidine