Solid-state NMR and molecular dynamics characterization of cannabinoid receptor-1 (CB1) helix 7 conformational plasticity in model membranes.
Little direct information is available regarding the influence of membrane environment on transmembrane (TM) G-protein-coupled receptor (GPCR) conformation and dynamics. The human CB1 cannabinoid receptor (hCB1) is a prominent GPCR pharmacotherapeutic target in which helix 7 appears critical to ligand recognition. We have chemically synthesized a hCB1 peptide corresponding to a segment of TM helix 7 and the entire contiguous helix 8 domain (fourth cytoplasmic loop) and reconstituted it in defined phospholipid-bilayer model membranes. Using an NMR-based strategy combined with molecular dynamics simulations, we provide the first direct experimental description of the orientation of hCB1 helix 7 in phospholipid membranes of varying thickness and the mechanism by which helix-7 conformation adjusts to avoid hydrophobic mismatch. Solid-state (15)N NMR data show that hCB1 helices 7 and 8 reconstituted into phospholipid bilayers are oriented in a TM and in-plane (i.e., parallel to the phospholipid membrane surface) fashion, respectively. TM helix orientation is influenced by the thickness of the hydrophobic membrane bilayer as well as the interaction of helix 8 with phospholipid polar headgroups. Molecular dynamics simulations show that a decrease in phospholipid chain-length induces a kink at P394 in TM helix 7 to avoid hydrophobic mismatch. Thus, the NP(X)nY motif found in hCB1 and highly conserved throughout the GPCR superfamily is important for flexing helix 7 to accommodate bilayer thickness. Dynamic modulation of hCB1-receptor TM helix conformation by its membrane environment may have general relevance to GPCR structure and function.
Center for Drug Discovery, Northeastern University, Boston, MA 02115, USA.
Elvis K
EK
Tiburu
Anna L
AL
Bowman
Jochem O
JO
Struppe
David R
DR
Janero
Hava K
HK
Avraham
Alexandros
A
Makriyannis
D000595:Amino Acid Sequence; D055592:Biophysical Phenomena; D002942:Circular Dichroism; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D019906:Nuclear Magnetic Resonance, Biomolecular; D010713:Phosphatidylcholines / Q000737:chemistry; D017433:Protein Structure, Secondary; D043884:Receptor, Cannabinoid, CB1 / Q000737:chemistry* / Q000235:genetics; D013816:Thermodynamics
D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D043884:Receptor, Cannabinoid, CB1; C028694:1-palmitoyl-2-oleoylphosphatidylcholine; D004134:Dimyristoylphosphatidylcholine