CRYSTAL-STRUCTURE AT 2.2-ANGSTROM RESOLUTION OF THE MHC-RELATED NEONATAL FC RECEPTOR

The three-dimensional structure of the rat neonatal Fe receptor (FcRn) is similar to the structure of molecules of the major histocompatibil ity complex (MHC). The counterpart of the MHC peptide-binding site is closed in FcRn, making the FcRn groove incapable of binding peptides. A dimer of FcRn heterodimers seen in the crystals may represent a rece ptor dimer that forms when the Fc portion of a single immunoglobulin b inds. An alternative use of the MHC fold for immune recognition is ind icated by the FcRn and FcRn/Fc co-crystal structures.