title: Characterization of nonsymbiotic tomato hemoglobin.
abstract: The nonsymbiotic tomato hemoglobin SOLly GLB1 (Solanum lycopersicon) is shown to form a homodimer of approximately 36 kDa with a high affinity for oxygen. Furthermore, our combined ultraviolet/visible, resonance Raman, and continuous wave electron paramagnetic resonance (EPR) measurements reveal that a mixture of penta- and hexacoordination of the heme iron is found in the deoxy ferrous form, whereas the ferric form shows predominantly a bis-histidine ligation (F8His-Fe(2+/3+)-E7His). This differs from the known forms of vertebrate hemoglobins and myoglobins. We have successfully applied our recently designed pulsed-EPR strategy to study the low-spin ferric form of tomato hemoglobin. These experiments reveal that, in ferric SOLly GLB1, one of the histidine planes is rotated 20 degrees (+/-10 degrees ) away from a N(heme)-Fe-N(heme) axis. Additionally, the observed g-values indicate a quasicoplanarity of the histidine ligands. From the HYSCORE (hyperfine sublevel correlation) measurements, the hyperfine and nuclear quadrupole couplings of the heme and histidine nitrogens are identified and compared with known EPR/ENDOR data of vertebrate Hbs and cytochromes. Finally, the ligand binding kinetics, which also indicate that the ferrous tomato Hb is only partially hexacoordinated, will be discussed in relation with the heme-pocket structure. The similarities and differences with other known nonsymbiotic plant hemoglobins will be highlighted.
authors.affiliation: Departments of Physics and Biomedical Sciences, University of Antwerp, Antwerp, Belgium.
authors.forename: A Iulia
authors.initials: AI
authors.lastname: Ioanitescu
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Laurent
authors.initials: L
authors.lastname: Kiger
authors.forename: Michael C
authors.initials: MC
authors.lastname: Marden
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
authors.forename: Sabine
authors.initials: S
authors.lastname: Van Doorslaer
mesh_terms: D000595:Amino Acid Sequence; D007700:Kinetics; D018551:Solanum lycopersicum / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000032:analysis / Q000737:chemistry*; D011487:Protein Conformation; D017386:Sequence Homology, Amino Acid; D013559:Symbiosis
chemical_list: D010940:Plant Proteins