PDBsum entry 5c6e

Oxygen transport

PDB id: 5c6e

Contents

Protein chains

141 a.a.

146 a.a.

Ligands

HEM ×2

CYN ×2

DOD ×123

PDB id:

5c6e

Name:

Oxygen transport

Title:

Joint x-ray/neutron structure of equine cyanomet hemoglobin in r state

Structure:

Hemoglobin subunit alpha. Chain: a. Synonym: alpha-globin,hemoglobin alpha chain. Hemoglobin subunit beta. Chain: b. Synonym: beta-globin,hemoglobin beta chain

Source:

Equus caballus. Horse. Organism_taxid: 9796. Organism_taxid: 9796

Resolution:

1.70Å R-factor: 0.210 R-free: 0.233

Authors:

S.Dajnowicz,S.Sean,B.L.Hanson,S.Z.Fisher,P.Langan,A.Y.Kovalevsky, T.C.Mueser

Key ref:

S.Dajnowicz et al. (2016). Visualizing the Bohr effect in hemoglobin: neutron structure of equine cyanomethemoglobin in the R state and comparison with human deoxyhemoglobin in the T state. Acta Crystallogr D Struct Biol, 72, 892-903. PubMed id: 27377386 DOI: 10.1107/S2059798316009049

Date:

22-Jun-15 Release date: 22-Jun-16

Protein chain

P01958  (HBA_HORSE) -  Hemoglobin subunit alpha from Equus caballus

Seq: 142 a.a.

Struc: 141 a.a.

Protein chain

P02062  (HBB_HORSE) -  Hemoglobin subunit beta from Equus caballus

Seq: 146 a.a.

Struc: 146 a.a.

DOI no: 10.1107/S2059798316009049

Acta Crystallogr D Struct Biol 72:892-903 (2016)

PubMed id: 27377386

Visualizing the Bohr effect in hemoglobin: neutron structure of equine cyanomethemoglobin in the R state and comparison with human deoxyhemoglobin in the T state.

S.Dajnowicz, S.Seaver, B.L.Hanson, S.Z.Fisher, P.Langan, A.Y.Kovalevsky, T.C.Mueser.

ABSTRACT

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:β1 dimer 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:β2 and α2:β1) to the cores of the individual monomers and to the dimer interfaces (α1:β1 and 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.