YWTD repeats are four-stranded beta-propeller repeats found in low-density lipoprotein receptors (LDLR). The six YWTD repeats together fold into a six-bladed beta-propeller (InterPro: IPR011042). Each blade of the propeller consists of four antiparallel beta-strands; the innermost strand of each blade is labeled 1 and the outermost strand, 4. The sequence repeats are offset with respect to the blades of the propeller, such that any given 40-residue YWTD repeat spans strands 24 of one propeller blade and strand 1 of the subsequent blade. This offset ensures circularization of the propeller because the last strand of the final sequence repeat acts as an innermost strand 1 of the blade that harbors strands 24 from the first sequence repeat. The repeat is found in a variety of proteins that include, vitellogenin receptor from Drosophila melanogaster, low-density lipoprotein (LDL) receptor,[1] preproepidermal growth factor, and nidogen (entactin).[2]
The LDLR regulates cholesterol homeostasis in mammalian cells. LDLR binds cholesterol-carrying LDL, associates with clathrin-coated pits, and is internalized into acidic endosomes where it separates from its ligand. The ligand is degraded in lysosomes, while the receptor returns to the cell surface.[3] The LDLR has several domains. The ligand-binding domain contains seven LDL receptor class A repeats, each with three disulphide bonds and a coordinated Ca2+ ion. The second conserved region contains two EGF repeats, followed by six YWTD or LDL receptor class B repeats and another EGF repeat.[4] This conserved region is critical for ligand release and recycling of the receptor.[5]
References
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