Formation of Two Hydrogen Bonds from the Globin to the Heme-Linked Oxygen Molecule in Ascaris Hemoglobin

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 91; no. 4; pp. 1594 - 1597
• Main Authors: De Baere, Ivo, Perutz, Max F., Kiger, Laurent, Marden, Michael C., Poyart, Claude
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 15.02.1994; National Acad Sciences; National Academy of Sciences
• Subjects: Absorption spectra; Allosteric Regulation; Analytical, structural and metabolic biochemistry; Animals; Ascaris - chemistry; Ascaris - genetics; Ascaris - metabolism; Biochemistry; Biochemistry. Physiology. Immunology. Molecular biology; Biological and medical sciences; Carbon monoxide; Carbon Monoxide - metabolism; Escherichia coli - genetics; Fundamental and applied biological sciences. Psychology; Hemoglobin; Hemoglobins; Hemoglobins - chemistry; Hemoglobins - genetics; Hemoglobins - metabolism; Hemoproteins; Hydrogen Bonding; Hydrogen bonds; Hydroxyls; Invertebrates; Metalloproteins; Models, Molecular; Nemathelminthia. Plathelmintha; Oxygen; Oxygen - chemistry; Oxygen - metabolism; Oxyhemoglobins - radiation effects; Phosphates; Physiology. Development; Proteins; Recombinant Proteins - chemistry; Sodium; Spectrophotometry; Spermatozoa; Tyrosine - chemistry; Tyrosine - genetics; Visible spectrum; Hemoprotein; Helmintha; Hemoglobin; Nemathelminthia; Oxygen affinity; Property structure relationship; Invertebrata; Nematoda; Ascaris; Hydrogen bond
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.91.4.1594

We have tried to find out why Ascaris hemoglobin has such an exceptionally high oxygen affinity (P50≈ 0.004 mmHg; 1 mmHg = 133 Pa). Following Kloek et al., we have synthesized the N-terminal globin domain of Ascaris hemoglobin in Escherichia coli [Kloek, A. P., Yang, J., Mathews, F. S. \& Goldberg, D. (1993) J. Biol. Chem. 268, 17669-17671]. Like Kloek et al., we found its oxygen affinity to be as high as that of native Ascaris hemoglobin. We thought that this high affinity might be due to the heme-bound oxygen molecule being stabilized by two hydrogen bonds from the globin instead of the usual one. Ascaris hemoglobin has a distal glutamine instead of the more usual histidine as one of the potential hydrogen bond donors. In addition, it contains a tyrosine at position 10 of B helix (B10) in place of the leucine generally found there in vertebrate myoglobins and hemoglobins. Following the discovery of Carver et al. that sperm whale myoglobin with the replacement of leucine B10 by phenylalanine has a raised oxygen affinity, we have replaced tyrosine B10 in the N-terminal domain of Ascaris hemoglobin by either leucine or phenylalanine [Carver, T. E., Brantley, R. E., Jr., Singleton, E. W., Arduini, R. M., Quillin, H. L., Phillips, G. N., Jr., \& Olson, J. S. (1992) J. Biol. Chem. 267, 14443-14450]. Either of these replacements lowered the oxygen affinity about 100-fold, to the same level of that of human α-globin chains. These results are consistent with a hydrogen bond linking the tyrosine hydroxyl to the heme-linked oxygen, with a bond energy of 2.7 kcal/mol.