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.
Department of Biochemistry, Biophysics and Molecular Biology, Iowa State University, Ames, IA 50010, USA.
James T
JT
Trent
Suman
S
Kundu
Julie A
JA
Hoy
Mark S
MS
Hargrove
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