Barbara M. F. Pearse

Adaptor protein 180 (AP180) and its homolog, clathrin assembly lymphoid myeloid leukemia protein (CALM), are closely related proteins that play important roles in clathrin-mediated endocytosis. Here, we present the structure of the NH2-terminal domain of CALM bound to phosphatidylinositol-4,5- bisphosphate [PtdIns(4,5)P2] via a lysine-rich motif. This motif is found in other proteins predicted to have domains of similar structure (for example, Huntingtin interacting protein 1). The structure is in part similar to the epsin NH2-terminal (ENTH) domain, but epsin lacks the PtdIns(4,5)P2-binding site. Because AP180 could bind to PtdIns(4,5)P2 and clathrin simultaneously, it may serve to tether clathrin to the membrane. This was shown by using purified components and a budding assay on preformed lipid monolayers. In the presence of AP180, clathrin lattices formed on the monolayer. When AP2 was also present, coated pits were formed.

CONTENTS INTRODUCTION 15 1 COAT COMPONENTS 153 Clathrin Triskelions and Adaptors ....... 153 Function and Distribution of Adaptors 156 COATED PITS AS MOLECULAR FILTERS ......... ... .. 159 Clathrin-Mediated Endocytosis. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 159 Clathrin-Mediated Intracellular Sorting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 62 Defective Sorting in Yeast Cells Lacking Clathrin ... 165 Interaction of Receptors with Adaptors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 CONCLUSIONS AND PROBLEMS 167

Coated vesicles have been purified from brain, adrenal medulla, and a nonsecreting lymphoma cell line. A single major protein species, clathrin, with an apparent molecular weight of 180,000, forms the coat of all these vesicles. Peptide mapping suggests that the amino acid sequence of clathrin is conserved, irrespective of tissue or species studied. Coated vesicles of different sizes are found. The coats are constructed with variable numbers of clathrin subunits, arranged in closed networks of hexagons and pentagons. The amount of clathrin in lymphoma cells suggests that coated vesicles transfer substantial amounts of membrane within cells, not necessarily in association with a secretory process.

The Hippo pathway was initially discovered in Drosophila melanogaster as a key regulator of tissue growth. It is an evolutionarily conserved signaling cascade regulating numerous biological processes, including cell growth and fate decision, organ size ...Read More