Giα and β Proteins Associate in a Complex with Cannabinoid Receptor Interacting Protein 1a (CRIP1a)

Abstract

Cannabis usage in recent years has increased due to the legalization of both recreational and medical use. The CB1cannabinoid receptor (CB1R) is a G‐protein coupled receptor (GPCR) found in the central nervous system and modulates neuroprogenitor development, neural commitment and migration, and neurotransmitter release. Cannabinoid receptor interacting protein 1a (CRIP1a) is a beta‐barrel protein that interacts with CB1R. Fluorescence polarization studies demonstrated that CRIP1a interacts directly with myristoylated Gαi (Booth et. al. 2021). We hypothesized that this occurs through the intercalation of the myristoyl moiety into the interior of the barrel through a gapped site that is bordered by the C‐terminal β‐strand. We tested this hypothesis by immunoprecipitation of CRIP1a with antibodies developed to two different epitopes of CRIP1a: to the loop‐helix‐loop motif that is located at a distance from the proposed myristoylated peptide access site, and to the C‐terminal β‐strand of CRIP1a which is directly adjacent to this region. We immunoprecipitated CRIP1a from N18TG2 mouse neuroblastoma cell homogenates without the addition of detergent for solubilization. We then probed for CRIP1a and determined if the either the Gαi subunit or the Gβγ dimer were associated with CRIP1a. Immunoprecipitation using the antibody to CRIP1a directed at the loop‐helix‐loop motif revealed complexes with Gai1 and Gai3 and not Gβγ. In contrast, immunoprecipitation of CRIP1a using the antibody directed at the C‐terminal β‐strand co‐immunoprecipitated Gβ and not Gαi1 or Gαi3. Collectively, these data suggest CRIP1a is a cargo‐carrying protein capable of carrying the G‐protein α‐subunit, but also exhibits an interaction with the β‐subunit.