title: Unusual heme iron-lipid acyl chain coordination in Escherichia coli flavohemoglobin.
abstract: Escherichia coli flavohemoglobin is endowed with the notable property of binding specifically unsaturated and/or cyclopropanated fatty acids both as free acids or incorporated into a phospholipid molecule. Unsaturated or cyclopropanated fatty acid binding to the ferric heme results in a spectral change observed in the visible absorption, resonance Raman, extended x-ray absorption fine spectroscopy (EXAFS), and x-ray absorption near edge spectroscopy (XANES) spectra. Resonance Raman spectra, measured on the flavohemoglobin heme domain, demonstrate that the lipid (linoleic acid or total lipid extracts)-induced spectral signals correspond to a transition from a five-coordinated (typical of the ligand-free protein) to a hexacoordinated, high spin heme iron. EXAFS and XANES measurements have been carried out both on the lipid-free and on the lipid-bound protein to assign the nature of ligand in the sixth coordination position of the ferric heme iron. EXAFS data analysis is consistent with the presence of a couple of atoms in the sixth coordination position at 2.7 A in the lipid-bound derivative (bonding interaction), whereas a contribution at 3.54 A (nonbonding interaction) can be singled out in the lipid-free protein. This last contribution is assigned to the CD1 carbon atoms of the distal LeuE11, in full agreement with crystallographic data on the lipid-free protein at 1.6 A resolution obtained in the present work. Thus, the contributions at 2.7 A distance from the heme iron are assigned to a couple of carbon atoms of the lipid acyl chain, possibly corresponding to the unsaturated carbons of the linoleic acid.
authors.affiliation: Department of Chemistry University "La Sapienza", Rome, and Istituto Nazionale per la Fisica della Materia UdF, Camerino, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: D'Angelo
authors.forename: Debora
authors.initials: D
authors.lastname: Lucarelli
authors.forename: Stefano
authors.initials: S
authors.lastname: della Longa
authors.forename: Maurizio
authors.initials: M
authors.lastname: Benfatto
authors.forename: Jean Louis
authors.initials: JL
authors.lastname: Hazemann
authors.forename: Alessandro
authors.initials: A
authors.lastname: Feis
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
authors.forename: Andrea
authors.initials: A
authors.lastname: Ilari
authors.forename: Alessandra
authors.initials: A
authors.lastname: Bonamore
authors.forename: Alberto
authors.initials: A
authors.lastname: Boffi
mesh_terms: D003001:Cloning, Molecular; D003460:Crystallization; D004093:Dihydropteridine Reductase / Q000737:chemistry*; D004926:Escherichia coli / Q000737:chemistry; D029968:Escherichia coli Proteins / Q000737:chemistry*; D005227:Fatty Acids / Q000737:chemistry*; D006418:Heme / Q000737:chemistry*; D006420:Hemeproteins / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry*; D008958:Models, Molecular; D009247:NADH, NADPH Oxidoreductases / Q000737:chemistry*; D013057:Spectrum Analysis
chemical_list: D029968:Escherichia coli Proteins; D005227:Fatty Acids; D006420:Hemeproteins; D008055:Lipids; D006418:Heme; D007501:Iron; D004093:Dihydropteridine Reductase; C076538:hmp protein, E coli; D009247:NADH, NADPH Oxidoreductases