The peculiar heme pocket of the 2/2 hemoglobin of cold-adapted Pseudoalteromonas haloplanktis TAC125.

HOWES BD; DANIELA GIORDANO; LEONARDO BOECHI; ROBERTA RUSSO; S MUCCIACCIARO; C CIACCIO; F SINIBALDI; M FITTIPALDI; MARCELO A. MARTI; DARIO A ESTRIN; MASSIMO COLETTA; CINZIA VERDE; GIULETTA SMULEVICH

JOURNAL OF BIOLOGICAL INORGANIC CHEMISTRY

SPRINGER

Año: 2011 p. 299 - 311

0949-8257

Abstract The genome of the cold-adapted bacteriumPseudoalteromonas haloplanktis TAC125 contains multi-ple genes encoding three distinct monomeric hemoglobinsexhibiting a 2/2 a-helical fold. In the present work, one ofthese hemoglobins is studied by resonance Raman, elec-tronic absorption and electronic paramagnetic resonancespectroscopies, kinetic measurements, and different bioin-formatic approaches. It is the first cold-adapted bacterialhemoglobin to be characterized. The results indicate thatthis protein belongs to the 2/2 hemoglobin family, GroupII, characterized by the presence of a tryptophanyl residueon the bottom of the heme distal pocket in position G8 andtwo tyrosyl residues (TyrCD1 and TyrB10). However,unlike other bacterial hemoglobins, the ferric state, inaddition to the aquo hexacoordinated high-spin form,shows multiple hexacoordinated low-spin forms, whereeither TyrCD1 or TyrB10 can likely coordinate the iron. This is the first example in which both TyrCD1 andTyrB10 are proposed to be the residues that are alternatively involved in heme hexacoordination by endogenous ligands.