Visualizing the Bohr effect in hemoglobin: neutron structure of equine cyanomethemoglobin in the R state and comparison with human deoxyhemoglobin in the T state
- Univ. of Toledo, OH (United States). Dept. of Chemistry and Biochemistry
- European Spallation Source (ESS), Lund (Sweden). Scientific Activities Division. Science Directorate
- Univ. of Toledo, OH (United States). Dept. of Chemistry and Biochemistry; Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Biology and Soft Matter Division
Neutron crystallography provides direct visual evidence of the atomic positions of deuterium-exchanged H atoms, enabling the accurate determination of the protonation/deuteration state of hydrated biomolecules. Comparison of two neutron structures of hemoglobins, human deoxyhemoglobin (T state) and equine cyanomethemoglobin (R state), offers a direct observation of histidine residues that are likely to contribute to the Bohr effect. Previous studies have shown that the T-state N-terminal and C-terminal salt bridges appear to have a partial instead of a primary overall contribution. Four conserved histidine residues [αHis72(EF1), αHis103(G10), αHis89(FG1), αHis112(G19) and βHis97(FG4)] can become protonated/deuterated from the R to the T state, while two histidine residues [αHis20(B1) and βHis117(G19)] can lose a proton/deuteron. αHis103(G10), located in the α1:β1dimer interface, appears to be a Bohr group that undergoes structural changes: in the R state it is singly protonated/deuterated and hydrogen-bonded through a water network to βAsn108(G10) and in the T state it is doubly protonated/deuterated with the network uncoupled. The very long-term H/D exchange of the amide protons identifies regions that are accessible to exchange as well as regions that are impermeable to exchange. The liganded relaxed state (R state) has comparable levels of exchange (17.1% non-exchanged) compared with the deoxy tense state (T state; 11.8% non-exchanged). Interestingly, the regions of non-exchanged protons shift from the tetramer interfaces in the T-state interface (α1:β2and α2:β1) to the cores of the individual monomers and to the dimer interfaces (α1:β1and α2:β2) in the R state. The comparison of regions of stability in the two states allows a visualization of the conservation of fold energy necessary for ligand binding and release.
- Research Organization:
- Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- Grant/Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1625838
- Journal Information:
- Acta Crystallographica. Section D. Structural Biology, Vol. 72, Issue 7; ISSN 2059-7983
- Publisher:
- IUCrCopyright Statement
- Country of Publication:
- United States
- Language:
- English
Neutron macromolecular crystallography
|
journal | February 2018 |
Direct visualization of critical hydrogen atoms in a pyridoxal 5′-phosphate enzyme
|
journal | October 2017 |
Similar Records
Comparison of the state of deoxyhemoglobin S molecules in solution and in fibers by hydrogen exchange kinetics
Preliminary neutron and X-ray crystallographic studies of equine cyanomethemoglobin