O2 and CO Binding Properties of Artificial Hemoproteins Formed by Complexing Iron Protoporphyrin IX with Human Serum Albumin Mutants
- 20 October 2005
- journal article
- research article
- Published by American Chemical Society (ACS) in Journal of the American Chemical Society
- Vol. 127 (45), 15933-15942
- https://doi.org/10.1021/ja054819u
Abstract
The binding properties of O2 and CO to recombinant human serum albumin (rHSA) mutants with a prosthetic heme group have been physicochemically and kinetically characterized. Iron(III) protoporphyrin IX (hemin) is bound in subdomain IB of wild-type rHSA [rHSA(wt)] with weak axial coordination by Tyr-161. The reduced ferrous rHSA(wt)-heme under an Ar atmosphere exists in an unusual mixture of four- and five-coordinate complexes and is immediately autoxidized by O2. To confer O2 binding capability on this naturally occurring hemoprotein, a proximal histidine was introduced into position Ile-142 or Leu-185 by site-directed mutagenesis. A single mutant (I142H) and three double mutants (I142H/Y161L, I142H/Y161F, and Y161L/L185H) were prepared. Both rHSA(I142H/Y161L)-heme and rHSA(I142H/Y161F)-heme formed ferrous five-N-coordinate high-spin complexes with axial ligation of His-142 under an Ar atmosphere. These artificial hemoproteins bind O2 at room temperature. Mutation at the other side of the porphyrin, Y161L/L185H, also allowed O2 binding to the heme. In contrast, the single mutant rHSA(I142H)-heme could not bind O2, suggesting that removal of Y161 is necessary to confer reversible O2 binding. Laser flash photolysis experiments showed that the kinetics of CO recombination with the rHSA(mutant)-heme were biphasic, whereas O2 rebinding exhibited monophasic kinetics. This could be due to the two different geometries of the axial imidazole coordination arising from the two orientations of the porphyrin plane in the heme pocket. The O2 binding affinities of the rHSA(mutant)-heme were significantly lower than those of hemoglobin and myoglobin, principally due to the high O2 dissociation rates. Changing Leu-161 to Phe-161 at the distal side increased the association rates of both O2 and CO, which resulted in enhanced binding affinity.Keywords
This publication has 39 references indexed in Scilit:
- Hemopexin: Structure, Function, and RegulationDNA and Cell Biology, 2002
- The Atomic Structure of Human Methemalbumin at 1.9 ÅBiochemical and Biophysical Research Communications, 2002
- Crystallographic analysis reveals common modes of binding of medium and long-chain fatty acids to human serum albuminJournal of Molecular Biology, 2000
- Physicochemical Properties and O2-Coordination Structure of Human Serum Albumin Incorporating Tetrakis(o-pivalamido)phenylporphyrinatoiron(II) DerivativesBioconjugate Chemistry, 1998
- A Comparison of Functional and Structural Consequences of the Tyrosine B10 and Glutamine E7 Motifs in Two Invertebrate Hemoglobins (Ascaris suum and Lucina pectinata)Biochemistry, 1997
- Model studies of iron-tyrosinate proteinsJournal of the American Chemical Society, 1985
- Structure of human oxyhaemoglobin at 2·1resolutionJournal of Molecular Biology, 1983
- Heme orientational disorder in reconstituted and native sperm whale myoglobin: Proton nuclear magnetic resonance characterizations by heme methyl deuterium labeling in the met-cyano proteinJournal of Molecular Biology, 1983
- Real space refinement of neutron diffraction data from sperm whale carbonmonoxymyoglobinJournal of Molecular Biology, 1981
- Visible and near-infrared magnetic circular dichroism spectra of high spin iron(III) complexes of protoporphyrin-IX-dimethylester. Characterization of charge-transfer bands of high spin heme [Fe(III)]Journal of Inorganic Biochemistry, 1980