Protonation states of histidine and other key residues in deoxy normal human adult hemoglobin by neutron protein crystallography
- Bioscience Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)
- Kyoto University, Research Reactor Institute, Kumatori, Osaka 590-0494 (Japan)
- Jichi Medical University, Department of Physiology, Shimotsuke, Tochigi 329-0498 (Japan)
- Protein Design Laboratory, Yokohama City University, 1-7-29 Suehiro, Tsurumi, Yokohama 230-0045 (Japan)
Using neutron diffraction analysis, the protonation states of 35 of 38 histidine residues were determined for the deoxy form of normal human adult hemoglobin. Distal and buried histidines may contribute to the increased affinity of the deoxy state for hydrogen ions and its decreased affinity for oxygen compared with the oxygenated form. The protonation states of the histidine residues key to the function of deoxy (T-state) human hemoglobin have been investigated using neutron protein crystallography. These residues can reversibly bind protons, thereby regulating the oxygen affinity of hemoglobin. By examining the OMIT F{sub o} − F{sub c} and 2F{sub o} − F{sub c} neutron scattering maps, the protonation states of 35 of the 38 His residues were directly determined. The remaining three residues were found to be disordered. Surprisingly, seven pairs of His residues from equivalent α or β chains, αHis20, αHis50, αHis58, αHis89, βHis63, βHis143 and βHis146, have different protonation states. The protonation of distal His residues in the α{sub 1}β{sub 1} heterodimer and the protonation of αHis103 in both subunits demonstrates that these residues may participate in buffering hydrogen ions and may influence the oxygen binding. The observed protonation states of His residues are compared with their ΔpK{sub a} between the deoxy and oxy states. Examination of inter-subunit interfaces provided evidence for interactions that are essential for the stability of the deoxy tertiary structure.
- OSTI ID:
- 22351217
- Journal Information:
- Acta Crystallographica. Section D: Biological Crystallography, Journal Name: Acta Crystallographica. Section D: Biological Crystallography Journal Issue: Pt 11 Vol. 66; ISSN ABCRE6; ISSN 0907-4449
- Country of Publication:
- Denmark
- Language:
- English
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