title: Functional characterization of the dimerization domain of the ferric uptake regulator (Fur) of Pseudomonas aeruginosa.
abstract: The functional properties of the recombinant C-terminal dimerization domain of the Pseudomonas aeruginosa Fur (ferric uptake regulator) protein expressed in and purified from Escherichia coli have been evaluated. Sedimentation velocity measurements demonstrate that this domain is dimeric, and the UV CD spectrum is consistent with a secondary structure similar to that observed for the corresponding region of the crystallographically characterized wild-type protein. The thermal stability of the domain as determined by CD spectroscopy decreases significantly as pH is increased and increases significantly as metal ions are added. Potentiometric titrations (pH 6.5) establish that the domain possesses a high-affinity and a low-affinity binding site for metal ions. The high-affinity (sensory) binding site demonstrates association constants (K(A)) of 10(+/-7)x10(6), 5.7(+/-3)x10(6), 2.0(+/-2)x10(6) and 2.0(+/-3)x10(4) M(-1) for Ni2+, Zn2+, Co2+ and Mn2+ respectively, while the low-affinity (structural) site exhibits association constants of 1.3(+/-2)x10(6), 3.2(+/-2)x10(4), 1.76(+/-1)x10(5) and 1.5(+/-2)x10(3) M(-1) respectively for the same metal ions (pH 6.5, 300 mM NaCl, 25 degrees C). The stability of metal ion binding to the sensory site follows the Irving-Williams order, while metal ion binding to the partial sensory site present in the domain does not. Fluorescence experiments indicate that the quenching resulting from binding of Co2+ is reversed by subsequent titration with Zn2+. We conclude that the domain is a reasonable model for many properties of the full-length protein and is amenable to some analyses that the limited solubility of the full-length protein prevents.
authors.affiliation: Immunological Detection Centre of Huhhot 253 Hospital, Inner Mongolia, 010051, People's Republic of China.
authors.forename: Erdeni
authors.initials: E
authors.lastname: Bai
authors.forename: Federico I
authors.initials: FI
authors.lastname: Rosell
authors.forename: Bao
authors.initials: B
authors.lastname: Lige
authors.forename: Marcia R
authors.initials: MR
authors.lastname: Mauk
authors.forename: Barbara
authors.initials: B
authors.lastname: Lelj-Garolla
authors.forename: Geoffrey R
authors.initials: GR
authors.lastname: Moore
authors.forename: A Grant
authors.initials: AG
authors.lastname: Mauk
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D019281:Dimerization; D004795:Enzyme Stability; D004926:Escherichia coli / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D011550:Pseudomonas aeruginosa / Q000378:metabolism*; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D013696:Temperature; D015032:Zinc
chemical_list: D001426:Bacterial Proteins; D012097:Repressor Proteins; C068477:ferric uptake regulating proteins, bacterial; D015032:Zinc