Synthetic Mimics of Small Mammalian Cell Surface Receptors

摘要

Receptors on the surface of mammalian cells promote the uptake of cell-impermeable ligands by receptor-mediated endocytosis. To mimic this process, we synthesized small molecules designed to project anti-dinitrophenyl antibody-binding motifs from the surface of living Jurkat lymphocytes. These synthetic receptors comprise N-alkyl derivatives of 3β-cholesterylamine as the plasma membrane anchor linked to 2,4-dinitrophenyl (DNP) and structurally similar fluorescent 7-nitrobenz-2-oxa-1,3-diazole (NBD) headgroups. Insertion of two β-alanine subunits between a DNP derivative and 3β-cholesterylamine yielded a receptor that avidly associates with cell surfaces (cellular t_(1/2) ～ 20 h). When added to Jurkat cells at 10 μM, this receptor enhanced uptake of an anti-DNP IgG ligand by ～ 200-fold in magnitude and ～ 400-fold in rate within 4 h (ligand internalization t_(1/2) ～ 95 min at 37℃). This non-natural receptor mimics many natural receptors by dynamically cycling between plasma membranes and intracellular endosomes (recycling t_(1/2) ～ 3 min), targeting of protein ligands to proposed cholesterol and sphingolipid-enriched lipid raft membrane microdomains, and delivery of protein ligands to late endosomes/lysosomes. Quantitative dithionite quenching of fluorescent extracellular NBD headgroups demonstrated that other 3β-cholesteryl-amine derivatives bearing fewer β-alanines in the linker region or N-acyl derivatives of 3β-cholesterylamine were less effective receptors due to more extensive trafficking to internal membranes. Synthetic cell surface receptors have potential applications as cellular probes, tools for drug delivery, and methods to deplete the rape utically important extracellular ligands.