The coatomer, which is a cytosolic protein complex that binds to dilysine motifs and reversibly associates with Golgi non-clathrin-coated vesicles, which further mediate biosynthetic protein transport from the ER, via the Golgi up to the trans Golgi network. Coatomer complexes are hetero-oligomers composed of at least an alpha, beta, beta', gamma, delta, epsilon and zeta subunit. It is a heptameric complex that can polymerize into a cage to deform the membrane into a bud. In mammals, the coatomer can only be recruited by membranes associated to ADP-ribosylation factors (ARFs), which are small GTP-binding proteins; the complex also influences the Golgi structural integrity, as well as the processing, activity, and endocytic recycling of LDL receptors. This model corresponds to the WD-associated region (WDAD) found in coatomer subunits alpha, beta, and beta' and is composed of a beta-propeller and an alpha-solenoid. The WD40 domain is found in a number of eukaryotic proteins that cover a wide variety of functions including adaptor/regulatory modules in signal transduction, pre-mRNA processing and cytoskeleton assembly. It typically contains a GH dipeptide 11-24 residues from its N-terminus and the WD dipeptide at its C-terminus and is 40 residues long, hence the name WD40. Between the GH and WD lies a conserved core. It forms a propeller-like structure with several blades where each blade is composed of a four-stranded anti-parallel b-sheet. Each WD40 sequence repeat forms the first three strands of one blade and the last strand in the next blade. The last C-terminal WD40 repeat completes the blade structure of the first WD40 repeat to create the closed ring propeller-structure. The residues on the top and bottom surface of the propeller are proposed to coordinate interactions with other proteins and/or small ligands allowing them to bind either stably or reversibly.
Jiyao W et al.(2023). "The conserved domain database in 2023.",