Stuart A. Kornfeld, M.D.

DEPARTMENT OF Internal Medicine
Keywords: intracellular trafficking, lysosome, mannose 6-phosphate, receptor

We are studying the biochemical and molecular basis for protein trafficking in mammalian cells, focusing on the biogenesis of lysosomes. The targeting of lysosomal enzymes from their site of synthesis in the rough endoplasmic reticulum to their final destination in lysosomes is a multistep process that utilizes a series of recognition signals that must be deciphered by cellular components that mediate the sorting, packaging and transport of the lysosomal enzymes. A key step in this pathway is the selective phosphorylation of mannose residues on the lysosomal enzymes. These residues allow binding to Man-6-P receptors in the Golgi and transport to lysosomes via clathrin-coated vesicles.

The goal of our work is to understand this complex sorting system at the molecular level. Currently we are studying how the enzyme that mediates mannose phosphorylation recognizes lysosomal enzymes as specific substrates and how the Man-6-P receptors bind their ligands, enter clathrin-coated pits, and traffic between various cellular compartments. We are using an in vitro assay to dissect the steps involved in the formation of clathrin-coated vesicles on Golgi membranes and liposomes.

Recently we discovered that a newly described family of coat proteins termed GGAs bind the acidic cluster/dileucine lysosomal sorting motif on the cytoplasmic tails of the Man-6-P receptors. Our findings indicate that the GGAs function as connectors to transfer the Man-6-P receptors to AP-1 clathrin-coated vesicles. We are studying how these complex protein-protein interactions are regulated,including the use of RNAi to selectively deplete cells of the various GGA species.