Cells require ordered movement of proteins and lipids from one membrane-bound compartment to another, while maintaining the organization, function and heterogeneity of the donor and acceptor membranes;vesicular membrane traffic carries out these functions. Clathrin coated vesicles are the most prominent form of traffic from the plasma membrane to endosomes (endocytosis), a pathway by which various ligands and their receptors enter cells. Clathrin coated vesicles are also important for traffic between endosomes and the trans-Golgi network (TGN). We propose to continue our studies of molecular mechanisms in clathrin-mediated membrane traffic, using direct observation by live-cell imaging with single-molecular sensitivity and high spatial and temporal resolution, to answer the following questions. (1) What are the molecular events required to initiate formation of a clathrin coated pit? (2) What are the molecular components of coats trapped at various stages of growth and closure: early and late abortive coated pits, and pits stalled at a relatively late stage, by imposing tension of the membrane and by inhibiting actin dynamics? (3) What is the mechanism of clathrin uncoating mediated by Hsc70 and its co-chaperone auxilin and how is the uncoating coordinated with assembly so that the two processes do not compete?
Vesicular membrane traffic is the principal mechanism for moving proteins and lipids among membrane-bound compartments in a cell. Clathrin coated vesicles are the most prominent form of traffic from the plasma membrane to endosomes (endocytosis), a pathway by which ligands such as hormones, transferrin, immunoglobulins, LDL, viruses and their receptors enter cells.
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