The<unk>  triskelion is composed of three<unk>  heavy chains interacting at their C-termini, each ~190 kDa heavy chain has a ~25 kDa light chain tightly bound to it. The three heavy chains provide the structural backbone of the<unk>  lattice, and the three light chains are thought to regulate the formation and disassembly of a<unk>  lattice. There are two forms of<unk>  light chains, designated a and b. The main<unk>  heavy chain, located on chromosome 17 in humans, is found in all cells. A second<unk>  heavy chain gene, on chromosome 22, is expressed in muscle.<unk>  heavy chain is often described as a leg, with subdomains, representing the foot (the N-terminal domain), followed by the ankle, distal leg, knee, proximal leg, and trimerization domains. The N-terminal domain consists of a seven-bladed β-propeller structure. The other domains form a super-helix of short alpha helices. This was originally determined from the structure of the proximal leg domain that identified and is composed of a smaller structural module referred to as<unk>  heavy chain repeat motifs. The light chains bind primarily to the proximal leg portion of the heavy chain with some interaction near the trimerization domain. The β-propeller at the 'foot' of<unk>  contains multiple binding sites for interaction with other proteins. When triskelia assemble together in solution, they can interact with enough flexibility to form 6-sided rings (hexagons) that yield a flat lattice, or 5-sided rings (pentagons) that are necessary for curved lattice formation. When many triskelions connect, they can form a basket-like structure. The structure shown, is built of 36 triskelia, one of which is shown in blue. Another common assembly is a truncated icosahedron. To enclose a vesicle, exactly 12 pentagons must be present in the lattice. In a cell,<unk>  triskelion in the cytoplasm binds to an adaptor protein that has bound membrane, linking one of its three feet to the membrane at a time.<unk>  cannot bind to membrane or cargo directly and instead uses adaptor proteins to do this. This triskelion will bind to other membrane-attached triskelia to form a rounded lattice of hexagons and pentagons, reminiscent of the panels on a soccer ball, that pulls the membrane into a bud. By constructing different combinations of 5-sided and 6-sided rings, vesicles of different sizes may assemble. The smallest<unk>  cage commonly imaged, called a mini-coat, has 12 pentagons and only two hexagons. Even smaller cages with zero hexagons probably do not form from the native protein, because the feet of the triskelia are too bulky.
Clathrin
Internexin
Apamin
Peripherin
Tetraspanin
Telokin
Reelin
Dystrophin