Robust Expression of the Human Neonatal Fc Receptor in a Truncated Soluble Form and as a Full-Length Membrane-Bound Protein in Fusion with eGFP

HeLa cells expressing human neonatal Fc receptor fused to eGFP

Serum proteins circulating in the blood are often being degraded in the lysosomes of cells that have endocytosed them. The exception is immunoglobulin G and human serum albumin that are rescued by the neonatal Fc receptor. When IgG and HSA are endocytosed and reaches the endosome they are bound by the FcRn at pH under 6.5. The FcRn rapidly transports the proteins back to the cell surface where they are released at pH 7.4 of the blood. This is why IgG and HSA has such extraordinary long serum circulation half-lifes. In this video we can see a part of a HeLa cell transduced with eGFP fused to human FcRn played at 2.5 times real time speed. The eGFP fused FcRn moves around beautifully in what appears to be endosomes and vesicles. Long half-life is vital for new biopharmaceuticals and the FcRn is an important target in the endeavor to deliver the next generations of protein therapeutics.