A Synthetic Mimic of Human Fc Receptors:  Defined Chemical Modification of Cell Surfaces Enables Efficient Endocytic Uptake of Human Immunoglobulin-G

Binding of ligands to macromolecular receptors on the surface of mammalian cells often results in ligand uptake through receptor-mediated endocytosis. Certain human leukocytes and epithelial cells express Fc receptors (FcRs) that bind and internalize antibodies through this mechanism. To mimic this process, we synthesized an artificial FcR comprising the membrane anchor N-alkyl-3β-amino-5α-cholestane linked to a disulfide-constrained cyclic peptide, termed FcIII, known to exhibit high affinity and specificity for the Fc region of human IgG. Treatment of human Jurkat lymphocytes that lack natural FcRs with the synthetic FcR (1 μM, 1 h) installed an average of ∼6.2 × 105 synthetic receptor molecules per cell surface. These treated cells gained the capacity to internalize human IgG at levels greater than human THP-1 cells that express the natural receptors FcγRI and FcγRII. By linking binding motifs for circulating ligands to membrane anchors that cycle between the cell surface and intracellular endosomes, minimalistic cell surface receptors can be used to destroy targeted ligands by endocytosis. These small mimics of macromolecular receptors may be useful for controlling the extracellular abundance of ligands involved in disease.