Interactions of the G protein-coupled receptor-associated sorting proteins (GASP) 1 and 2 with the novel cannabinoid receptor GPR55

Background GPR55 was recently found to be a novel cannabinoid receptor containing a seven transmembrane-spanning domain and being a member of the G protein-coupled receptor (GPCR) subfamily A. GPR55 is activated by different cannabinoid ligands as well as by the lipid ligand lysophosphatidylinositol (LPI). Generally, the activity of GPCRs is coordinated by receptor signaling, receptor desensitization and receptor resensitization. The latter two mechanisms are typically associated with the sorting of the GPCRs between degradation or recycling pathways and are highly regulated. Several sorting proteins have recently been identified, for example the G protein-coupled receptor-associated sorting protein-1 (GASP1). GASP1 was originally found to target δ opioid receptors (DORs) to lysosomes, hence a degradative pathway. Moreover, it was shown that the interface of the DORGASP1 protein-protein interaction is predominantly located in the C-terminal portion of the receptor protein.