Spectroscopic characterization of a truncated hemoglobin from the nitrogen-fixing bacterium Herbaspirillum seropedicae.
The Herbaspirillum seropedicae genome sequence encodes a truncated hemoglobin typical of group II (Hs-trHb1) members of this family. We show that His-tagged recombinant Hs-trHb1 is monomeric in solution, and its optical spectrum resembles those of previously reported globins. NMR analysis allowed us to assign heme substituents. All data suggest that Hs-trHb1 undergoes a transition from an aquomet form in the ferric state to a hexacoordinate low-spin form in the ferrous state. The close positions of Ser-E7, Lys-E10, Tyr-B10, and His-CD1 in the distal pocket place them as candidates for heme coordination and ligand regulation. Peroxide degradation kinetics suggests an easy access to the heme pocket, as the protein offered no protection against peroxide degradation when compared with free heme. The high solvent exposure of the heme may be due to the presence of a flexible loop in the access pocket, as suggested by a structural model obtained by using homologous globins as templates. The truncated hemoglobin described here has unique features among truncated hemoglobins and may function in the facilitation of O(2) transfer and scavenging, playing an important role in the nitrogen-fixation mechanism.
Centro Nacional de Ressonância Magnética Nuclear, Jiri Jonas, Departamento de Bioquímica Médica, ICB/CCS/UFRJ, Rio de Janeiro, RJ, Brazil.
Guilherme
G
Razzera
Javier
J
Vernal
Debora
D
Baruh
Viviane I
VI
Serpa
Carolina
C
Tavares
Flávio
F
Lara
Emanuel M
EM
Souza
Fábio O
FO
Pedrosa
Fábio C L
FC
Almeida
Hernán
H
Terenzi
Ana Paula
AP
Valente
D000042:Absorption; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism; D002942:Circular Dichroism; D006418:Heme / Q000378:metabolism; D042803:Herbaspirillum / Q000737:chemistry* / Q000378:metabolism*; D007700:Kinetics; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009584:Nitrogen / Q000378:metabolism*; D010545:Peroxides / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013056:Spectrophotometry, Ultraviolet; D054793:Truncated Hemoglobins / Q000737:chemistry* / Q000378:metabolism
D001426:Bacterial Proteins; D008024:Ligands; D010545:Peroxides; D011994:Recombinant Proteins; D054793:Truncated Hemoglobins; D006418:Heme; D009584:Nitrogen