Neutron diffraction reveals oxygen–histidine hydrogen bond in oxymyoglobin

Myoglobin (Mb) reversibly binds molecular oxygen in vertebrate muscle and consists of a polypeptide chain of 153 residues and one haem, which closely resembles one subunit of a haemoglobin (Hb) tetramer. In oxygenated myglobin (oxyMb) the iron atom is coordinated by four porphyrin nitrogen atoms, Nε of the invariant ‘proximal’ histidine (F8), and molecular oxygen1. The oxygen molecule lies in a tight pocket, bounded by two hydrophobic groups (Phe CD1 Val E11) and the side chain of the ‘distal’ histidine (E7). This histidine is present in Hb and Mb of many different organisms, with substitution by glutamine or leucine found in only a few cases. The function of the residue is not clear, although it does present steric hindrance to linear ligands such as carbon monoxide and favours ‘bent’ ones, such as O2. We report here that the imidazole stabilizes bound molecular oxygen with a hydrogen bond, as revealed by neutron diffraction analysis.

[1]  Russell S. Drago,et al.  Spin-pairing model of dioxygen binding and its application to various transition-metal systems as well as hemoglobin cooperativity , 1980 .

[2]  J. Alberi,et al.  A two-dimensional position-sensitive detector for thermal neutrons , 1975 .

[3]  W. Goddard,et al.  Molecular description of dioxygen bonding in hemoglobin. , 1977, Proceedings of the National Academy of Sciences of the United States of America.

[4]  L. Pauling,et al.  Nature of the Iron–Oxygen Bond in Oxyhæmoglobin , 1964, Nature.

[5]  C. Reed,et al.  On the bonding of FeO2 in hemoglobin and related dioxygen complexes. , 1977, Proceedings of the National Academy of Sciences of the United States of America.

[6]  JOSEPH J. WEISS,et al.  Nature of the Iron–Oxygen Bond in Oxyhæmoglobin , 1964, Nature.

[7]  M. Ikeda-Saito,et al.  Studies on cobalt myoglobins and hemoglobins. Interaction of sperm whale myoglobin and Glycera hemoglobin with molecular oxygen. , 1977, The Journal of biological chemistry.

[8]  S. Phillips,et al.  Structure and refinement of oxymyoglobin at 1.6 A resolution. , 1980, Journal of molecular biology.

[9]  D. A. Case,et al.  Binding of oxygen and carbon monoxide to hemoglobin. An analysis of the ground and excited states , 1979 .

[10]  M. Brunori,et al.  Oxygenation and EPR spectral properties of Aplysia myoglobins containing cobaltous porphyrins. , 1978, Biochimica et biophysica acta.

[11]  B. Schoenborn,et al.  Neutron Diffraction Analysis of Myoglobin , 1969, Nature.

[12]  T. Yonetani,et al.  Studies on cobalt myoglobins and hemoglobins. 3. Electron paramagnetic resonance studies of reversible oxygenation of cobalt myoglobins and hemoglobins. , 1974, The Journal of biological chemistry.