title: The optical spectra of fluoride complexes can effectively probe H-bonding interactions in the distal cavity of heme proteins.
abstract: Fluoride complexes of heme proteins are characterized by unique spectroscopic properties, that provide a simple and direct means to monitor the interactions of the distal heme pocket environment with the iron-bound ligand. In particular, a strong correlation has been demonstrated between the wavelength of the iron-porphyrin charge transfer band at 600-620nm (CT1) and the strength of H-bonding donation from the distal amino acid side chains to the fluoride ion. In parallel, resonance Raman spectra with excitation within either the CT1 band or the charge transfer band at 450-460nm (CT2) have revealed that the iron-fluoride stretching frequency is directly affected by H-bonding to the fluoride ion. On this basis, globins and peroxidases display distinct spectroscopic features, which are strongly dependent on the capability of their distal residues (i.e. histidine, arginine and tryptophan) to be involved in H-bonding with the ligand. In particular, in peroxidases strong H-bonding corresponds to a low iron-fluoride stretching frequency and to a red-shifted CT1 band. The reverse is observed in myoglobin. Interestingly, a truncated hemoglobin of microbial origin (Thermobifida fusca) investigated in the present work, displays the specific spectroscopic signature of a peroxidase, in agreement with the presence of strong H-bonding residues, i.e., tyrosine and tryptophan, within the distal pocket.
authors.affiliation: Dipartimento di Chimica Ugo Schiff, Università di Firenze, Via della Lastruccia 3-13, Sesto Fiorentino, Florence, Italy.
authors.forename: Enrica
authors.initials: E
authors.lastname: Droghetti
authors.forename: Francesco P
authors.initials: FP
authors.lastname: Nicoletti
authors.forename: Alessandra
authors.initials: A
authors.lastname: Bonamore
authors.forename: Natascia
authors.initials: N
authors.lastname: Sciamanna
authors.forename: Alberto
authors.initials: A
authors.lastname: Boffi
authors.forename: Alessandro
authors.initials: A
authors.lastname: Feis
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
mesh_terms: D005459:Fluorides / Q000737:chemistry*; D006420:Hemeproteins / Q000737:chemistry*; D006860:Hydrogen Bonding; D011485:Protein Binding; D013059:Spectrum Analysis, Raman; D054793:Truncated Hemoglobins / Q000737:chemistry
chemical_list: D006420:Hemeproteins; D054793:Truncated Hemoglobins; D005459:Fluorides