Sedimentation equilibrium analysis of recombinant mouse FcRn with murine IgG1.

The interaction of mouse IgG1 or IgG1-derived Fc fragment with recombinant, insect cell expressed mouse FcRn has been analyzed using sedimentation equilibrium. This results in a model for the interaction in which the two binding sites for FcRn on Fc or IgG1 have significantly different affinities with macroscopic binding constants of < 130 nM and 6 microM. This data indicates the formation of an asymmetric FcRn:Fc (or IgG1):FcRn complex which is consistent with earlier suggestions that for this form of recombinant FcRn, binding to IgG1 or Fc does not result in a symmetric 2:1 complex in which both binding sites are equivalent.