Clathrin is a triskelion-shaped cytoplasmic protein that polymerizes into a
polyhedral lattice on intracellular membranes to form protein-coated membrane
vesicles. Lattice formation induces the sorting of membrane proteins during
endocytosis and organelle biogenesis by interacting with membrane-associated
adaptor molecules. Clathrin functions as a trimer, and these trimers, or
triskelions, are comprised of three legs joined by a central vertex. Each leg
consists of one heavy chain and one light chain. The clathrin heavy-chain
contains a 145-residue repeat that is present in seven copies [1,2]. The
clathrin heavy-chain repeat (CHCR) is also found in nonclathrin proteins such
as Pep3, Pep5, Vam6, Vps41, and Vps8 from Saccharomyces cerevisiae and their
orthologs from other eukaryotes [1,3,4,5]. These proteins, like clathrins, are
involved in vacuolar maintenance and protein sorting. The CHCR repeats in
these proteins could mediate protein-protein interactions, or possibly
represent clathrin-binding domains, or perform clathrin-like functions. CHCR
repeats in the clathrin heavy chain, Saccharomyces cerevisiae Vamp2 and human
Vamp6 have been implicated in homooligomerization, suggesting that this may be
the primary function of this repeat.
The CHCR repeat folds into an elongated right-handed superhelix coil of short
α-helices (see <PDB:1B89>) . Individual 'helix-turn-helix-loop' or
helix hairpin units comprise the canonical repeat and stack along the
superhelix axis to form a single extended domain. The canonical hairpin repeat
of the clathrin superhelix resembles a tetratrico peptide repeat (TPR) (see
<PDOC50005>), but is shorter and lacks the characteristic spacing of the
hydrophobic residues in TPRs.
The profile we developed covers the entire CHCR repeat.
April 2013 / First entry.
PROSITE method (with tools and information) covered by this documentation:
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.
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