The hydrophobic amino acid residues in the membrane-proximal C tail of the G protein-coupled vasopressin V2 receptor are necessary for transport-competent receptor folding

Abstract

It is believed that the membrane-proximal C tail of the G protein-coupled receptors forms an additional alpha helix with amphipathic properties (helix 8). It was previously shown for the vasopressin V2 receptor (V2R) that a conserved dileucine motif (L 339, L 340) in this putative helix 8 is necessary for endoplasmic reticulum (ER) to Golgi transfer of the receptor. Here, we demonstrate that the other hydrophobic residues forming the non-polar side of this helix (F 328, V 332 and L 336) are also transport-relevant. In contrast, the multiple serine residues contributing to the more hydrophilic side (S 330, S 331, S 333, S 334, S 338) do not influence receptor trafficking. In addition, we show unambiguously by the use of pharmacological chaperones that the hydrophobic residues of the putative helix 8 do not form a transport signal necessary for receptor sorting into ER to Golgi vesicles. Instead, they are necessary to establish a transport-competent folding state in the early secretory pathway.