FIGURE 1.

The topological information for RTP4 (A) and the schematic interaction between RTP4 and MOPr-DOPr heteromers (B). The data was obtained via UniProt data base (uniprot.org). RTP4 (249 amino acids) has a single predicted transmembrane domain (228th to 248th amino acids) located near the C-terminal end. It is considered that the N-terminal end is intracellular (1st to 227th amino acids) and the C-terminal end (249th amino acid) is extracellular, with no signal peptide (UniProt,https://www.uniprot.org/uniprot/Q9ER80) (A). Decaillot et al. (2008) have suggested that the interaction between RTP4 and MOPr-DOPr heteromer occurs in the cytoplasmic region since the region within the MOPr cytoplasmic C-terminal 29 amino acid residues (i.e., 370–398 aa) was necessary for interaction with RTP4 (B).