Clathrin-coated vesicles

Roth T and Porter K (1964)

Clathrin-coated vesicles" are intracellular particles with a diameter of 50-250 nm, which are covered on the cytoplasmic side by a spiky coating in which the protein clathrin (relative molecular mass 650 000) forms the main constituent. Furthermore, the 900 amino acid long dynamin, which can bind and hydrolyze GTP, is found in this vesicle coat. Clathrin-coated vesicles are formed at the Golgi apparatus. They are involved in the vesicular transport of substances between the Golgi apparatus, lysosomes and other organelles.

The clathrin-coated vesicles are formed from the so-called coated pits during endocytosis (e.g. of macromolecules) induced by specific receptors. Coated pits are depressions in the plasma membrane of the cell, which are formed by small invaginations of the plasma membrane. Shortly after their formation, coated vesicles lose their clathrin protein coat. An ATP-dependent protein, the uncoating ATPase, removes clathrin from the vesicles.

Such "coatless" vesicles are also called early endosomes. The early endosome is the sorting station of the cell. It ensures that not all internalized substances are degraded in lysosomes. Early endosomes can fuse with certain other vesicles (sorting vesicles) to form so-called late endosomes. Late endosomes are characterized by a lowered pH value inside (pH 5-6). As a result, ligands and receptors dissociate inside them. The ligands accumulate in the lumen of the vesicles. The receptors collect in small tubular protrusions of the vesicle membrane. These are then pinched off with their contents and can be recycled. The remaining vesicle with the remaining ligands, now fuses with lysosomes. There they are degraded by lysosomal enzymes and further utilized. Proteins, for example, are broken down into their amino acid fraction. LDL particles are cleaved into fatty acids and cholesterol.

Clathrin-mediated endocytosis is responsible for the receptor-mediated uptake of important transport proteins such as LDL (low density lipoprotein) and transferrin, as well as for the uptake of growth factors and peptide hormones (Lakkaraju A et al. 2002).

1. Lakkaraju A et al ( (2002). Low-density lipoprotein receptor-related protein mediates the endocytosis of anionic liposomes in neurons. J Biol Chem 277: 15085-15092.
2. Roth T and Porter K (1964). Yolk protein uptake in the oocyte of the mosquito Aedes aegypti. J Cell Biol 20: 313 - 330.