Crystal Structure of Haptocorrin in Complex with CNCbl

Experimental Data Snapshot

  • Resolution: 2.35 Å
  • R-Value Free: 0.226 
  • R-Value Work: 0.196 
  • R-Value Observed: 0.197 

Starting Models: experimental
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This is version 2.1 of the entry. See complete history


Structural basis for universal corrinoid recognition by the cobalamin transport protein haptocorrin.

Furger, E.Frei, D.C.Schibli, R.Fischer, E.Prota, A.E.

(2013) J Biol Chem 288: 25466-25476

  • DOI: https://doi.org/10.1074/jbc.M113.483271
  • Primary Citation of Related Structures:  
    4KKI, 4KKJ

  • PubMed Abstract: 

    Cobalamin (Cbl; vitamin B12) is an essential micronutrient synthesized only by bacteria. Mammals have developed a sophisticated uptake system to capture the vitamin from the diet. Cbl transport is mediated by three transport proteins: transcobalamin, intrinsic factor, and haptocorrin (HC). All three proteins have a similar overall structure but a different selectivity for corrinoids. Here, we present the crystal structures of human HC in complex with cyanocobalamin and cobinamide at 2.35 and 3.0 Å resolution, respectively. The structures reveal that many of the interactions with the corrin ring are conserved among the human Cbl transporters. However, the non-conserved residues Asn-120, Arg-357, and Asn-373 form distinct interactions allowing for stabilization of corrinoids other than Cbl. A central binding motif forms interactions with the e- and f-side chains of the corrin ring and is conserved in corrinoid-binding proteins of other species. In addition, the α- and β-domains of HC form several unique interdomain contacts and have a higher shape complementarity than those of intrinsic factor and transcobalamin. The stabilization of ligands by all of these interactions is reflected in higher melting temperatures of the protein-ligand complexes. Our structural analysis offers fundamental insights into the unique binding behavior of HC and completes the picture of Cbl interaction with its three transport proteins.

  • Organizational Affiliation

    From the Center for Radiopharmaceutical Sciences and.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Transcobalamin-1467Homo sapiensMutation(s): 0 
Gene Names: TC1TCN1
UniProt & NIH Common Fund Data Resources
Find proteins for P20061 (Homo sapiens)
Explore P20061 
Go to UniProtKB:  P20061
GTEx:  ENSG00000134827 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP20061
Glycosylation Sites: 7Go to GlyGen: P20061-1
Sequence Annotations
  • Reference Sequence
Small Molecules
Ligands 4 Unique
IDChains Name / Formula / InChI Key2D Diagram3D Interactions
Query on CNC

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C63 H89 Co N14 O14 P
Query on NAG

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B [auth A]
C [auth A]
D [auth A]
E [auth A]
F [auth A]
B [auth A],
C [auth A],
D [auth A],
E [auth A],
F [auth A],
G [auth A],
H [auth A]
C8 H15 N O6
Query on PEG

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K [auth A]
L [auth A]
M [auth A]
N [auth A]
O [auth A]
K [auth A],
L [auth A],
M [auth A],
N [auth A],
O [auth A],
P [auth A],
Q [auth A],
R [auth A],
S [auth A],
T [auth A],
U [auth A]
C4 H10 O3
Query on CA

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Experimental Data & Validation

Experimental Data

  • Resolution: 2.35 Å
  • R-Value Free: 0.226 
  • R-Value Work: 0.196 
  • R-Value Observed: 0.197 
  • Space Group: P 64
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 149.89α = 90
b = 149.89β = 90
c = 57.49γ = 120
Software Package:
Software NamePurpose
RemDAqdata collection
XDSdata reduction
XDSdata 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: 2013-07-17
    Type: Initial release
  • Version 1.1: 2013-10-09
    Changes: Database references
  • Version 1.2: 2017-11-15
    Changes: Refinement description
  • Version 1.3: 2020-07-29
    Type: Remediation
    Reason: Carbohydrate remediation
    Changes: Data collection, Database references, Derived calculations, Structure summary
  • Version 2.0: 2021-08-18
    Changes: Data collection, Database references, Derived calculations, Non-polymer description, Structure summary
  • Version 2.1: 2023-09-20
    Changes: Data collection, Refinement description