Model of ARH interactions with AP-1B and LDLR in REs. (A) Schematic depicting amino acids of the cytoplasmic tail of LDLR. Clathrin-coated pit (CCP) and proximal and distal targeting determinants are underlined. Red residues are critically important for either proximal or distal signal. Green residues denote clusters of acidic residues that are part of the sorting determinants. Arrows denote the position of amino acid residues in the cytoplasmic tail of LDLR. (B and C) Model depicting biosynthetic sorting of LDLR-CT27 from the TGN into REs. Here, LDLR-CT27 engages ARH and AP-1B for basolateral exocytosis (B). In cells expressing ARH(R266A), the interaction between ARH and AP-1B is broken and exocytosis of LDLR-CT27 is stalled (C).