title: The peculiar heme pocket of the 2/2 hemoglobin of cold-adapted Pseudoalteromonas haloplanktis TAC125.
abstract: The genome of the cold-adapted bacterium Pseudoalteromonas haloplanktis TAC125 contains multiple genes encoding three distinct monomeric hemoglobins exhibiting a 2/2 α-helical fold. In the present work, one of these hemoglobins is studied by resonance Raman, electronic absorption and electronic paramagnetic resonance spectroscopies, kinetic measurements, and different bioinformatic approaches. It is the first cold-adapted bacterial hemoglobin to be characterized. The results indicate that this protein belongs to the 2/2 hemoglobin family, Group II, characterized by the presence of a tryptophanyl residue on the bottom of the heme distal pocket in position G8 and two tyrosyl residues (TyrCD1 and TyrB10). However, unlike other bacterial hemoglobins, the ferric state, in addition to the aquo hexacoordinated high-spin form, shows multiple hexacoordinated low-spin forms, where either TyrCD1 or TyrB10 can likely coordinate the iron. This is the first example in which both TyrCD1 and TyrB10 are proposed to be the residues that are alternatively involved in heme hexacoordination by endogenous ligands.
authors.affiliation: Dipartimento di Chimica, Università di Firenze, 50019, Sesto Fiorentino (FI), Italy.
authors.forename: Barry D
authors.initials: BD
authors.lastname: Howes
authors.forename: Daniela
authors.initials: D
authors.lastname: Giordano
authors.forename: Leonardo
authors.initials: L
authors.lastname: Boechi
authors.forename: Roberta
authors.initials: R
authors.lastname: Russo
authors.forename: Simona
authors.initials: S
authors.lastname: Mucciacciaro
authors.forename: Chiara
authors.initials: C
authors.lastname: Ciaccio
authors.forename: Federica
authors.initials: F
authors.lastname: Sinibaldi
authors.forename: Maria
authors.initials: M
authors.lastname: Fittipaldi
authors.forename: Marcelo A
authors.initials: MA
authors.lastname: Martí
authors.forename: Darío A
authors.initials: DA
authors.lastname: Estrin
authors.forename: Guido
authors.initials: G
authors.lastname: di Prisco
authors.forename: Massimo
authors.initials: M
authors.lastname: Coletta
authors.forename: Cinzia
authors.initials: C
authors.lastname: Verde
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D006454:Hemoglobins / Q000737:chemistry / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D010084:Oxidation-Reduction; D031161:Pseudoalteromonas / Q000378:metabolism*; D013696:Temperature
chemical_list: D001426:Bacterial Proteins; D006454:Hemoglobins