Three-Dimensional Structure of Hemoglobin from the Polychaete Annelid, Glycera dibranchiata, at 2.5 A Resolution

The three-dimensional structure of hemoglobin from the bloodworm, Glycera dibranchiata, has been determined crystallographically to a resolution of 2.5 A using three isomorphous heavy atom derivatives. Approximately 79% of the 147 amino acid residues are in seven helical segments which are disposed in the familiar myoglobin fold. The heme group is enclosed in a hydrophobic cavity which is formed by the particular folding of the polypeptide chain. The D helix is absent and the position usually occupied by the distal histidine in vertebrate hemoglobins is occupied by leucine.