InterPro domain: IPR012331

Proteins synthesized on the ribosome and processed in the endoplasmic reticulum are transported from the Golgi apparatus to the trans-Golgi network (TGN), and from there via small carrier vesicles to their final destination compartment. These vesicles have specific coat proteins (such as clathrin or coatomer) that are important for cargo selection and direction of transport [ 1 ]. Clathrin coats contain both clathrin (acts as a scaffold) and adaptor complexes that link clathrin to receptors in coated vesicles. Clathrin-associated protein complexes are believed to interact with the cytoplasmic tails of membrane proteins, leading to their selection and concentration. The two major types of clathrin adaptor complexes are the heterotetrameric adaptor protein (AP) complexes, and the monomeric GGA (Golgi-localising, Gamma-adaptin ear domain homology, ARF-binding proteins) adaptors [ 2 , 3 ].

Clathrin is a trimer composed of three heavy chains and three light chains, each monomer projecting outwards like a leg; this three-legged structure is known as a triskelion [ 4 , 5 ]. The heavy chains form the legs, their N-terminal beta-propeller regions extending outwards, while their C-terminal alpha-alpha-superhelical regions form the central hub of the triskelion. Peptide motifs can bind between the beta-propeller blades. The light chains appear to have a regulatory role, and may help orient the assembly and disassembly of clathrin coats as they interact with hsc70 uncoating ATPase [ 6 ]. Clathrin triskelia self-polymerise into a curved lattice by twisting individual legs together. The clathrin lattice forms around a vesicle as it buds from the TGN, plasma membrane or endosomes, acting to stabilise the vesicle and facilitate the budding process [ 7 ]. The multiple blades created when the triskelia polymerise are involved in multiple protein interactions, enabling the recruitment of different cargo adaptors and membrane attachment proteins [ 7 ].

This entry represents the alpha-helical zigzag linker region connecting the conserved N-terminal beta-propeller region to the C-terminal alpha-alpha-superhelical region in clathrin heavy chains [ 8 ].

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