title: Unusual flexibility of distal and proximal histidine residues in the haem pocket of Drosophila melanogaster haemoglobin.
abstract: Several pH-dependent low-spin ferric haem forms are identified in a frozen solution of the ferric ¹²¹Cys→Ser mutant of Drosophila melanogaster haemoglobin (DmHb1*) using electron paramagnetic resonance (EPR) techniques. Different forms with EPR parameters typical of bis-histidine coordinated haem iron centers were observed. Strong pH-dependent changes in the EPR signatures were observed related to changes in the haem pocket. The pulsed EPR data indicate that both the distal and proximal histidine exhibit a large libration around the Fe-N(His) axis. The resonance Raman spectra of the CO-ligated ferrous form of Drosophila melanogaster haemoglobin are typical of an open conformation, with little stabilization of the CO ligand by the surrounding amino-acid residues. The EPR data of the cyanide-ligated ferric DmHb1* indicates a close similarity with cyanide-ligated ferric myoglobin. The structural characteristics of DmHb1* are found to clearly differ from those of other bis-histidine-coordinated globins.
authors.affiliation: Department of Physics, University of Antwerp, Wilrijk-Antwerp, Belgium. sabine.vandoorslaer@ua.ac.be
authors.forename: Anda Iulia
authors.initials: AI
authors.lastname: Ioanitescu
authors.forename: Sabine
authors.initials: S
authors.lastname: Van Doorslaer
authors.forename: Sylvia
authors.initials: S
authors.lastname: Dewilde
authors.forename: Luc
authors.initials: L
authors.lastname: Moens
mesh_terms: D000818:Animals; D029721:Drosophila Proteins / Q000737:chemistry*; D004331:Drosophila melanogaster / Q000737:chemistry* / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005914:Globins / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006639:Histidine / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D013056:Spectrophotometry, Ultraviolet
chemical_list: D029721:Drosophila Proteins; D006418:Heme; D006639:Histidine; D005914:Globins