title: Unusually strong H-bonding to the heme ligand and fast geminate recombination dynamics of the carbon monoxide complex of Bacillus subtilis truncated hemoglobin.
abstract: The active site of the oxygen-avid truncated hemoglobin from Bacillus subtilis has been characterized by infrared absorption and resonance Raman spectroscopies, and the dynamics of CO rebinding after photolysis has been investigated by picosecond transient absorption spectroscopy. Resonance Raman experiments on the CO bound adduct revealed the presence of two Fe-CO stretching bands at 545 and 520 cm-1, respectively. Accordingly, two C-O stretching bands at 1924 and 1888 cm-1 were observed in infrared absorption and resonance Raman measurements. The very low C-O stretching frequency at 1888 cm-1 (corresponding to the extremely high RR stretching frequency at 545 cm-1) indicates unusually strong hydrogen bonding between CO and distal residues. On the basis of a comparison with other truncated hemoglobin it is envisaged that the two CO conformers are determined by specific interactions with the TrpG8 and TyrB10 residues. Mutation of TrpG8 to Leu deeply alters the hydrogen-bonding network giving rise mainly to a CO conformer characterized by a Fe-CO stretching band at 489 cm-1 and a CO stretching band at 1958 cm-1. Picosecond laser photolysis experiments carried out on the CO bound adduct revealed dynamical processes that take place within a few nanoseconds after photolysis. Picosecond dynamics is largely dominated by CO geminate rebinding and is consistent with strong H-bonding contributions of TyrB10 and TrpG8 to ligand stabilization.
authors.affiliation: Dipartimento di Chimica, Università di Firenze, Via della Lastruccia 3, I-50019 Sesto Fiorentino (FI), Italy.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Feis
authors.forename: Andrea
authors.initials: A
authors.lastname: Lapini
authors.forename: Bruno
authors.initials: B
authors.lastname: Catacchio
authors.forename: Silvia
authors.initials: S
authors.lastname: Brogioni
authors.forename: Paolo
authors.initials: P
authors.lastname: Foggi
authors.forename: Emilia
authors.initials: E
authors.lastname: Chiancone
authors.forename: Alberto
authors.initials: A
authors.lastname: Boffi
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
mesh_terms: D001412:Bacillus subtilis / Q000737:chemistry*; D002248:Carbon Monoxide / Q000737:chemistry* / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D007700:Kinetics; D007834:Lasers; D008958:Models, Molecular; D009154:Mutation; D010782:Photolysis; D011485:Protein Binding; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013053:Spectrophotometry; D013055:Spectrophotometry, Infrared; D013059:Spectrum Analysis, Raman; D054793:Truncated Hemoglobins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism
chemical_list: D011994:Recombinant Proteins; D054793:Truncated Hemoglobins; D006418:Heme; D002248:Carbon Monoxide