Structure of the receptor-binding domain of human thrombopoietin determined by complexation with a neutralizing antibody fragment

Proc Natl Acad Sci U S A. 2004 Feb 17;101(7):1816-21. doi: 10.1073/pnas.0308530100. Epub 2004 Feb 9.


The cytokine thrombopoietin (TPO), the ligand for the hematopoietic receptor c-Mpl, acts as a primary regulator of megakaryocytopoiesis and platelet production. We have determined the crystal structure of the receptor-binding domain of human TPO (hTPO(163)) to a 2.5-A resolution by complexation with a neutralizing Fab fragment. The backbone structure of hTPO(163) has an antiparallel four-helix bundle fold. The neutralizing Fab mainly recognizes the C-D crossover loop containing the species invariant residue Q111. Titration calorimetric experiments show that hTPO(163) interacts with soluble c-Mpl containing the extracellular cytokine receptor homology domains with 1:2 stoichiometry with the binding constants of 3.3 x 10(9) M(-1) and 1.1 x 10(6) M(-1). The presence of the neutralizing Fab did not inhibit binding of hTPO(163) to soluble c-Mpl fragments, but the lower-affinity binding disappeared. Together with prior genetic data, these define the structure-function relationships in TPO and the activation scheme of c-Mpl.

MeSH terms

  • Amino Acid Sequence
  • Crystallography, X-Ray
  • Epitopes / chemistry
  • Epitopes / immunology
  • Humans
  • Immunoglobulin Fab Fragments / immunology*
  • Immunoglobulin Fab Fragments / metabolism
  • Models, Molecular
  • Molecular Sequence Data
  • Neoplasm Proteins / metabolism
  • Neutralization Tests
  • Protein Binding
  • Protein Conformation
  • Proto-Oncogene Proteins / metabolism
  • Receptors, Cytokine / metabolism
  • Receptors, Thrombopoietin
  • Solubility
  • Structure-Activity Relationship
  • Substrate Specificity
  • Thrombopoietin / chemistry*
  • Thrombopoietin / immunology
  • Thrombopoietin / metabolism*


  • Epitopes
  • Immunoglobulin Fab Fragments
  • Neoplasm Proteins
  • Proto-Oncogene Proteins
  • Receptors, Cytokine
  • Receptors, Thrombopoietin
  • MPL protein, human
  • Thrombopoietin

Associated data

  • PDB/1V7M
  • PDB/1V7N