Structural characterization of a group II 2/2 hemoglobin from the plant pathogen Agrobacterium tumefaciens.
Within the 2/2 hemoglobin sub-family, no group II 2/2Hbs from proteobacteria have been so far studied. Here we present the first structural characterization of a group II 2/2Hb from the soil and phytopathogenic bacterium Agrobacterium tumefaciens (At-2/2HbO). The crystal structure of ferric At-2/2HbO (reported at 2.1Å resolution) shows the location of specific/unique heme distal site residues (e.g., His(42)CD1, a residue distinctive of proteobacteria group II 2/2Hbs) that surround a heme-liganded water molecule. A highly intertwined hydrogen-bonded network, involving residues Tyr(26)B10, His(42)CD1, Ser(49)E7, Trp(93)G8, and three distal site water molecules, stabilizes the heme-bound ligand. Such a structural organization suggests a path for diatomic ligand diffusion to/from the heme. Neither a similar distal site structuring effect nor the presence of distal site water molecules has been so far observed in group I and group III 2/2Hbs, thus adding new distinctive information to the complex picture of currently available 2/2Hb structural and functional data. This article is part of a Special Issue entitled: Protein Structure and Function in the Crystalline State.
Department of Physics, University of Genova, I-16146 Genova, Italy.
Alessandra
A
Pesce
Marco
M
Nardini
Marie
M
Labarre
Christian
C
Richard
Jonathan B
JB
Wittenberg
Beatrice A
BA
Wittenberg
Michel
M
Guertin
Martino
M
Bolognesi
D016960:Agrobacterium tumefaciens / Q000737:chemistry* / Q000378:metabolism; D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D001665:Binding Sites; D003461:Crystallography; D006418:Heme / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry* / Q000378:metabolism; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016415:Sequence Alignment
D001426:Bacterial Proteins; D006454:Hemoglobins; D006418:Heme