Crystallographic analysis of synechocystis cyanoglobin reveals the structural changes accompanying ligand binding in a hexacoordinate hemoglobin.
The crystal structures of cyanide and azide-bound forms of the truncated hemoglobin from Synechocystis are presented at 1.8 angstroms resolution. A comparison with the structure of the endogenously liganded protein reveals a conformational shift unprecedented in hemoglobins, and provides the first picture of a hexacoordinate hemoglobin in both the bis-histidyl and the exogenously coordinated states. The structural changes between the different conformations are confined to two regions of the protein; the B helix, and the E helix, including the EF loop. A molecular "hinge" controlling movement of the E helix is observed in the EF loop, which is composed of three principal structural elements: Arg64, the heme-d-propionate, and a three-residue extension of the F helix. Additional features of the structural transition between the two protein conformations are discussed as they relate to the complex ligand-binding behavior observed in hexacoordinate hemoglobins, and the potential physiological function of this class of proteins.
Trent
James T
JT
Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50010, USA.
Kundu
Suman
S
Hoy
Julie A
JA
Hargrove
Mark S
MS
D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry*; D006454:Hemoglobins / Q000737:chemistry / Q000378:metabolism*; D008024:Ligands; D017550:Spectroscopy, Fourier Transform Infrared; D054793:Truncated Hemoglobins
D006454:Hemoglobins; D008024:Ligands; D054793:Truncated Hemoglobins