title: Interplay of the H-bond donor-acceptor role of the distal residues in hydroxyl ligand stabilization of Thermobifida fusca truncated hemoglobin.
abstract: The unique architecture of the active site of Thermobifida fusca truncated hemoglobin (Tf-trHb) and other globins belonging to the same family has stimulated extensive studies aimed at understanding the interplay between iron-bound ligands and distal amino acids. The behavior of the heme-bound hydroxyl, in particular, has generated much interest in view of the relationships between the spin-state equilibrium of the ferric iron atom and hydrogen-bonding capabilities (as either acceptor or donor) of the OH(-) group itself. The present investigation offers a detailed molecular dynamics and spectroscopic picture of the hydroxyl complexes of the WT protein and a combinatorial set of mutants, in which the distal polar residues, TrpG8, TyrCD1, and TyrB10, have been singly, doubly, or triply replaced by a Phe residue. Each mutant is characterized by a complex interplay of interactions in which the hydroxyl ligand may act both as a H-bond donor or acceptor. The resonance Raman stretching frequencies of the Fe-OH moiety, together with electron paramagnetic resonance spectra and MD simulations on each mutant, have enabled the identification of specific contributions to the unique ligand-inclusive H-bond network typical of this globin family.
authors.affiliation: Dipartimento di Chimica "Ugo Schiff", Università di Firenze , Via della Lastruccia 3-13, I-50019 Sesto Fiorentino (FI), Italy.
authors.forename: Francesco P
authors.initials: FP
authors.lastname: Nicoletti
authors.forename: Juan P
authors.initials: JP
authors.lastname: Bustamante
authors.forename: Enrica
authors.initials: E
authors.lastname: Droghetti
authors.forename: Barry D
authors.initials: BD
authors.lastname: Howes
authors.forename: Maria
authors.initials: M
authors.lastname: Fittipaldi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Bonamore
authors.forename: Paola
authors.initials: P
authors.lastname: Baiocco
authors.forename: Alessandro
authors.initials: A
authors.lastname: Feis
authors.forename: Alberto
authors.initials: A
authors.lastname: Boffi
authors.forename: Darío A
authors.initials: DA
authors.lastname: Estrin
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
mesh_terms: D000192:Actinomycetales / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D001665:Binding Sites / Q000235:genetics; D004578:Electron Spin Resonance Spectroscopy; D006418:Heme / Q000737:chemistry; D006860:Hydrogen Bonding; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008958:Models, Molecular; D056004:Molecular Dynamics Simulation; D016297:Mutagenesis, Site-Directed; D055550:Protein Stability; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013059:Spectrum Analysis, Raman; D054793:Truncated Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008024:Ligands; D011994:Recombinant Proteins; D054793:Truncated Hemoglobins; D006418:Heme