TY - JOUR T1 - Structural Domains of the CB1 Cannabinoid Receptor That Contribute to Constitutive Activity and G-Protein Sequestration JF - The Journal of Neuroscience JO - J. Neurosci. SP - 8758 LP - 8764 DO - 10.1523/JNEUROSCI.21-22-08758.2001 VL - 21 IS - 22 AU - Jingjiang Nie AU - Deborah L. Lewis Y1 - 2001/11/15 UR - http://www.jneurosci.org/content/21/22/8758.abstract N2 - The CB1 cannabinoid receptor is a constitutively active receptor that can sequester Gi/o-proteins and prevent other Gi/o-coupled receptors from signaling (Bouaboula et al., 1997; Pan et al., 1998; Vasquez and Lewis, 1999). G-protein sequestration occurs because the population of CB1 cannabinoid receptors exists in both an inactive G-protein-precoupled RGGDP state and a constitutively active R*GGTPstate. We tested the hypothesis that the distal C-terminal tail acts to prevent G-protein activation. We found that truncation of the distal C-terminal tail of the CB1 receptor (CB1–417) enhanced both the constitutive activity and the ability of the receptor to sequester G-proteins. In addition, we tested the hypothesis that the conserved aspartate (D2.50) in the second transmembrane domain of the CB1 cannabinoid receptor is crucial for constitutive activity and G-protein sequestration. We found that the mutation of aspartate to asparagine (CB1-D164N) abolished G-protein sequestration and constitutive receptor activity without disrupting agonist-stimulated activity. We conclude that the CB1-D164N mutation and the C-terminal truncation shift the population of receptors in opposite directions. The CB1-D164N mutation shifts the receptor into an inactive R state upcoupled from G-proteins, whereas the C-terminal truncation (CB1–417) shifts the receptor into the active R*GGTP state. Thus the distal C-terminal tail acts to constrain the receptor from activating G-proteins, whereas the aspartate (D2.50) in the second transmembrane domain stabilizes the receptor in both the inactive RGGDP state and the active R*GGTP state. ER -