Experimental Data Snapshot

  • Resolution: 1.86 Å
  • R-Value Free: 0.220 
  • R-Value Work: 0.184 

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Oligomerization and ligand binding in a homotetrameric hemoglobin: two high-resolution crystal structures of hemoglobin Bart's (gamma(4)), a marker for alpha-thalassemia.

Kidd, R.D.Baker, H.M.Mathews, A.J.Brittain, T.Baker, E.N.

(2001) Protein Sci 10: 1739-1749

  • DOI: https://doi.org/10.1110/ps.11701
  • Primary Citation of Related Structures:  
    1I3D, 1I3E

  • PubMed Abstract: 

    Hemoglobin (Hb) Bart's is present in the red blood cells of millions of people worldwide who suffer from alpha-thalassemia. alpha-Thalassemia is a disease in which there is a deletion of one or more of the four alpha-chain genes, and excess gamma and beta chains spontaneously form homotetramers. The gamma(4) homotetrameric protein known as Hb Bart's is a stable species that exhibits neither a Bohr effect nor heme-heme cooperativity. Although Hb Bart's has a higher O(2) affinity than either adult (alpha(2)beta(2)) or fetal (alpha(2)gamma(2)) Hbs, it has a lower affinity for O(2) than HbH (beta(4)). To better understand the association and ligand binding properties of the gamma(4) tetramer, we have solved the structure of Hb Bart's in two different oxidation and ligation states. The crystal structure of ferrous carbonmonoxy (CO) Hb Bart's was determined by molecular replacement and refined at 1.7 A resolution (R = 21.1%, R(free) = 24.4%), and that of ferric azide (N(3)(-)) Hb Bart's was similarly determined at 1.86 A resolution (R = 18.4%, R(free) = 22.0%). In the carbonmonoxy-Hb structure, the CO ligand is bound at an angle of 140 degrees, and with an unusually long Fe-C bond of 2.25 A. This geometry is attributed to repulsion from the distal His63 at the low pH of crystallization (4.5). In contrast, azide is bound to the oxidized heme iron in the methemoglobin crystals at an angle of 112 degrees, in a perfect orientation to accept a hydrogen bond from His63. Compared to the three known quaternary structures of human Hb (T, R, and R2), both structures most closely resemble the R state. Comparisons with the structures of adult Hb and HbH explain the association and dissociation behaviour of Hb homotetramers relative to the heterotetrameric Hbs.

  • Organizational Affiliation

    School of Biological Sciences, University of Auckland, Auckland, New Zealand.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
A, B
146Homo sapiensMutation(s): 0 
Gene Names: HBG1
UniProt & NIH Common Fund Data Resources
Find proteins for P69891 (Homo sapiens)
Explore P69891 
Go to UniProtKB:  P69891
PHAROS:  P69891
GTEx:  ENSG00000213934 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP69891
Sequence Annotations
  • Reference Sequence
Experimental Data & Validation

Experimental Data

  • Resolution: 1.86 Å
  • R-Value Free: 0.220 
  • R-Value Work: 0.184 
  • Space Group: P 21 21 2
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 60.541α = 90
b = 81.625β = 90
c = 53.036γ = 90
Software Package:
Software NamePurpose
MAR345data collection
DENZOdata reduction
SCALEPACKdata scaling

Structure Validation

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Ligand Structure Quality Assessment 

Entry History 

Deposition Data

Revision History  (Full details and data files)

  • Version 1.0: 2001-09-12
    Type: Initial release
  • Version 1.1: 2008-04-27
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Derived calculations, Version format compliance
  • Version 1.3: 2017-10-04
    Changes: Advisory, Refinement description
  • Version 2.0: 2024-02-07
    Changes: Advisory, Atomic model, Data collection, Database references, Derived calculations
  • Version 2.1: 2024-04-03
    Changes: Advisory, Derived calculations, Refinement description