Clathrin heavy chain
Bos taurus (bovine)
Endocytosis is one of the ways to take various molecules into a cell, in which a cell engulfs some of extracellular molecules through the formation of a vesicle from its cell membrane. In this process, Clathrin, a triskelion-shaped cytoplasmic protein, induces and helps the vesicle formation, polymerizing a polyhedral lattice on intracellular membrane to coat the vesicle.
The crystal structure of the homotrimer of the clathrin heavy chain has been determined. Three heavy-chain subunits radiate from the center of the trimer. The C-terminal domains at the center and the proximal domains near it are the important region called the "triskelion hub". Each fragment in the hub folds into a right-handed superhelix coil of the repeated short alpha-helices, and binds to the monomeric light chain. With regard to the clathrin self-assembly during the formation of a polyhedral lattice, it has been revealed from the structure model by cryo-electron microscopy that proximal domains from two different trimers interact with each other and these interactions require two lengthwise surfaces on each triskelion hub. Here, the crystal structure suggests that the paired helix-turn-helix motifs on the interface between the proximal domains stack each other, and moreover, the proximal domains associate via helix-face/helix-face contact, packing complementally between the ridge and groove of the surfaces, in which the hydrophobic patches on the surfaces may also contribute to the helix face to face contact. Thus, from this structure analysis, the mechanism of the clathrin self-assembly has been cleared.
Protein Data Bank (PDB)
Ybe, J.A. Brodsky, F.M. Hofmann, K. Lin, K. Liu, S.H. Chen, L. Earnest, T.N. Fletterick, R.J. Hwang, P.K.; "Clathrin self-assembly is mediated by a tandemly repeated superhelix."; Nature; (1999) 399:371-375 PubMed:10360576.
author: Yuko Tsuchiya