Clathrin is the scaffold protein of the basket-like coat that surrounds coated vesicles. The soluble assembly unit, a triskelion, contains three heavy chains and three light chains in an extended three-legged structure. Each leg contains one heavy and one light chain. The N-terminus of the heavy chain is known as the globular domain, and is composed of seven repeats which form a beta propeller [1].

1: Atomic structure of clathrin: a beta propeller terminal domain joins an alpha zigzag linker. ter Haar E, Musacchio A, Harrison SC, Kirchhausen T; Cell. 1998;95:563-573. PMID:9827808