High-affinity binding of the neonatal Fc receptor to its IgG ligand requires receptor immobilization

Biochemistry. 1997 Aug 5;36(31):9374-80. doi: 10.1021/bi970841r.


The neonatal Fc receptor (FcRn) binds maternal immunoglobulin G (IgG) during the acquisition of passive immunity by the fetus or newborn. In adult mammals, FcRn also binds IgG and returns it to the bloodstream, thus protecting IgG from a default degradative pathway. Biosensor assays have been used to characterize the interaction of a soluble form of FcRn with IgG. We use the statistical method of cross-validation to show that there are two classes of noninteracting binding sites, and these are sufficient to account for previously observed nonlinear Scatchard plots of FcRn/IgG binding data. We demonstrate that immobilization of FcRn on the biosensor surface reproduces the high-affinity IgG binding observed for membrane-bound FcRn, whereas immobilization of IgG results in lower affinity binding similar to that of the FcRn/IgG interaction in solution. The dependence of FcRn/IgG binding affinity on the coupled molecule provides further evidence in support of the previously hypothesized model that an FcRn dimer forms the high-affinity IgG binding site.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Animals, Newborn
  • Binding Sites
  • Biosensing Techniques
  • CHO Cells
  • Cricetinae
  • Immunoglobulin G / metabolism*
  • Kinetics
  • Protein Binding
  • Rats
  • Receptors, Fc / metabolism*
  • Recombinant Proteins / metabolism


  • Immunoglobulin G
  • Receptors, Fc
  • Recombinant Proteins