EFFECTS OF RECEPTOR DIMERIZATION ON THE INTERACTION BETWEEN THE CLASS-I MAJOR HISTOCOMPATIBILITY COMPLEX-RELATED FC RECEPTOR AND IGG

The neonatal Fc receptor (FcRn) transports maternal IgG from ingested milk in the gut to the bloodstream of newborn mammals. An FcRn dimer w as observed in crystals of the receptor alone and of an FcRn-Fc comple x, but its biological relevance was unknown. Here we use surface plasm on resonance-based biosensor assays to assess the role of FcRn dimeriz ation in IgG binding. We find high-affinity IgG binding when FcRn is i mmobilized on a biosensor chip in an orientation facilitating dimeriza tion but not when its orientation disrupts dimerization. This result s upports a model in which Igc-induced dimerization of FcRn is relevant for signaling the cell to initiate endocytosis of the IgG-FcRn complex .