Structure of Human Transcobalamin in complex with Cobalamin

Experimental Data Snapshot

  • Resolution: 3.20 Å
  • R-Value Free: 0.288 
  • R-Value Work: 0.257 
  • R-Value Observed: 0.258 

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This is version 1.4 of the entry. See complete history


Structural basis for mammalian vitamin B12 transport by transcobalamin.

Wuerges, J.Garau, G.Geremia, S.Fedosov, S.N.Petersen, T.E.Randaccio, L.

(2006) Proc Natl Acad Sci U S A 103: 4386-4391

  • DOI: https://doi.org/10.1073/pnas.0509099103
  • Primary Citation of Related Structures:  
    2BB5, 2BB6, 2BBC

  • PubMed Abstract: 

    Cobalamin (Cbl, vitamin B(12)) serves for two essential cofactors in mammals. The pathway for its intestinal absorption, plasma transport, and cellular uptake uses cell surface receptors and three Cbl-transporting proteins, haptocorrin, intrinsic factor, and transcobalamin (TC). We present the structure determination of a member of the mammalian Cbl-transporter family. The crystal structures of recombinant human and bovine holo-TCs reveal a two-domain architecture, with an N-terminal alpha(6)-alpha(6) barrel and a smaller C-terminal domain. One Cbl molecule in base-on conformation is buried inside the domain interface. Structural data combined with previous binding assays indicate a domain motion in the first step of Cbl binding. In a second step, the weakly coordinated ligand H(2)O at the upper axial side of added H(2)O-Cbl is displaced by a histidine residue of the alpha(6)-alpha(6) barrel. Analysis of amino acid conservation on TC's surface in orthologous proteins suggests the location of the TC-receptor-recognition site in an extended region on the alpha(6)-alpha(6) barrel. The TC structure allows for the mapping of sites of amino acid variation due to polymorphisms of the human TC gene. Structural information is used to predict the overall fold of haptocorrin and intrinsic factor and permits a rational approach to the design of new Cbl-based bioconjugates for diagnostic or therapeutic drug delivery.

  • Organizational Affiliation

    Centre of Excellence in Biocrystallography, Department of Chemical Sciences, University of Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy.

Find similar proteins by:  (by identity cutoff)  |  3D Structure
Entity ID: 1
MoleculeChains Sequence LengthOrganismDetailsImage
Transcobalamin II
A, B
409Homo sapiensMutation(s): 1 
Gene Names: TCN2TC2
UniProt & NIH Common Fund Data Resources
Find proteins for P20062 (Homo sapiens)
Explore P20062 
Go to UniProtKB:  P20062
PHAROS:  P20062
GTEx:  ENSG00000185339 
Entity Groups  
Sequence Clusters30% Identity50% Identity70% Identity90% Identity95% Identity100% Identity
UniProt GroupP20062
Sequence Annotations
  • Reference Sequence
Small Molecules
Experimental Data & Validation

Experimental Data

  • Resolution: 3.20 Å
  • R-Value Free: 0.288 
  • R-Value Work: 0.257 
  • R-Value Observed: 0.258 
  • Space Group: P 21 21 21
Unit Cell:
Length ( Å )Angle ( ˚ )
a = 49.127α = 90
b = 145.497β = 90
c = 165.043γ = 90
Software Package:
Software NamePurpose
SCALAdata scaling
PDB_EXTRACTdata extraction
MOSFLMdata reduction
CCP4data 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: 2006-04-04
    Type: Initial release
  • Version 1.1: 2008-05-01
    Changes: Version format compliance
  • Version 1.2: 2011-07-13
    Changes: Advisory, Version format compliance
  • Version 1.3: 2012-10-24
    Changes: Non-polymer description
  • Version 1.4: 2023-08-23
    Changes: Data collection, Database references, Derived calculations, Refinement description