Steric Trigger as a Mechanism for CB1 Cannabinoid Receptor Activation

To determine the moiety that behaves as the steric trigger to activate the CB(1) cannabinoid receptor, conformational properties of the nonclassical cannabinoid CP55244, one of the most potent CB(1) receptor agonists, were characterized by conformational analysis, rotational barrier calculations, and molecular dynamics (MD) simulations. It was shown from the present MD simulations that the torsion angles phi1 and phi4 of the C3 side chain showed the most dramatic change when compared with the ground-state receptor-bound conformation, indicating that rotation around these torsion angles is responsible for releasing the ligand strain energy. Multiple stages would be involved in the ligand conformational change. As a molecular mechanism for the ligand-induced CB(1) receptor conformational change, we propose that the C3 side chain serves as the steric trigger, while the ACD-ring moiety of CP55244 serves as the plug. Steric clash with helices within the binding pocket would induce microconformational adaptation within the protein. This mechanism would suggest that rotational flexibility in a ligand may be as important a determinant of agonist activity as the pharmacophoric elements that can be identified.

[1]  M. Grossmann,et al.  G Protein-coupled Receptors , 1998, The Journal of Biological Chemistry.

[2]  R. Mathies,et al.  Chromophore structure in lumirhodopsin and metarhodopsin I by time-resolved resonance Raman microchip spectroscopy. , 2001, Biochemistry.

[3]  D. Colquhoun,et al.  Binding, gating, affinity and efficacy: The interpretation of structure‐activity relationships for agonists and of the effects of mutating receptors , 1998, British journal of pharmacology.

[4]  D. Kendall,et al.  Ligand Binding and Modulation of Cyclic AMP Levels Depend on the Chemical Nature of Residue 192 of the Human Cannabinoid Receptor 1 , 1998, Journal of neurochemistry.

[5]  J. Klein-Seetharaman,et al.  Structure and function in rhodopsin: mapping light-dependent changes in distance between residue 65 in helix TM1 and residues in the sequence 306-319 at the cytoplasmic end of helix TM7 and in helix H8. , 2001, Biochemistry.

[6]  William J Welsh,et al.  Homology model of the CB1 cannabinoid receptor: Sites critical for nonclassical cannabinoid agonist interaction , 2003, Biopolymers.

[7]  J. Andreassi,et al.  Role of a conserved lysine residue in the peripheral cannabinoid receptor (CB2): evidence for subtype specificity. , 1999, Molecular pharmacology.

[8]  T. Steitz,et al.  Glucose-induced conformational change in yeast hexokinase. , 1978, Proceedings of the National Academy of Sciences of the United States of America.

[9]  J. Wess,et al.  Molecular Mechanisms Involved in Muscarinic Acetylcholine Receptor-mediated G Protein Activation Studied by Insertion Mutagenesis (*) , 1996, The Journal of Biological Chemistry.

[10]  B. Kobilka,et al.  G Protein-coupled Receptors , 1998, The Journal of Biological Chemistry.

[11]  J. Drews.  Drug discovery: a historical perspective. , 2000, Science.

[12]  K. Nakanishi,et al.  Movement of retinal along the visual transduction path. , 2000, Science.

[13]  A. Howlett,et al.  Determination and characterization of a cannabinoid receptor in rat brain. , 1988, Molecular pharmacology.

[14]  K. Fahmy,et al.  A conserved carboxylic acid group mediates light-dependent proton uptake and signaling by rhodopsin. , 1994, The Journal of biological chemistry.

[15]  P Ghanouni,et al.  Agonist-induced conformational changes in the G-protein-coupling domain of the β2 adrenergic receptor , 2001, Proceedings of the National Academy of Sciences of the United States of America.

[16]  E. Meng,et al.  Receptor activation: what does the rhodopsin structure tell us? , 2001, Trends in pharmacological sciences.

[17]  A. Howlett,et al.  Cannabinoid inhibition of adenylate cyclase. Pharmacology of the response in neuroblastoma cell membranes. , 1984, Molecular pharmacology.

[18]  M. Moussaif,et al.  Probing the mechanism of rhodopsin-catalyzed transducin activation. , 2001 .

[19]  Mark E. Tuckerman,et al.  Reversible multiple time scale molecular dynamics , 1992 .

[20]  J. Ballesteros,et al.  Activation of the β2-Adrenergic Receptor Involves Disruption of an Ionic Lock between the Cytoplasmic Ends of Transmembrane Segments 3 and 6* , 2001, The Journal of Biological Chemistry.

[21]  A. Howlett,et al.  Nonclassical cannabinoid analgetics inhibit adenylate cyclase: development of a cannabinoid receptor model. , 1988, Molecular pharmacology.

[22]  T. Sakmar,et al.  Rhodopsin: insights from recent structural studies. , 2002, Annual review of biophysics and biomolecular structure.

[23]  T. Halgren.  Merck molecular force field. I. Basis, form, scope, parameterization, and performance of MMFF94 , 1996, J. Comput. Chem..

[24]  R A Mathies,et al.  Vibrationally coherent photochemistry in the femtosecond primary event of vision. , 1994, Science.

[25]  T. Bonner,et al.  A lysine residue of the cannabinoid receptor is critical for receptor recognition by several agonists but not WIN55212-2. , 1996, Molecular pharmacology.

[26]  U. Gether.  Uncovering molecular mechanisms involved in activation of G protein-coupled receptors. , 2000, Endocrine reviews.

[27]  H. Bourne,et al.  G-protein diseases furnish a model for the turn-on switch , 1998, Nature.

[28]  M. Gelb,et al.  Mechanism of Rhodopsin Activation as Examined with Ring-constrained Retinal Analogs and the Crystal Structure of the Ground State Protein* , 2001, The Journal of Biological Chemistry.

[29]  D. Farrens,et al.  Conformational Changes in Rhodopsin , 1999, The Journal of Biological Chemistry.

[30]  S. W. Lin,et al.  Specific tryptophan UV-absorbance changes are probes of the transition of rhodopsin to its active state. , 1996, Biochemistry.

[31]  A. Howlett,et al.  Structure-activity relationships for cannabinoid receptor-binding and analgesic activity: studies of bicyclic cannabinoid analogs. , 1993, Molecular pharmacology.

[32]  F Guarnieri,et al.  Activation of the cannabinoid CB1 receptor may involve a W6 48/F3 36 rotamer toggle switch. , 2002, The journal of peptide research : official journal of the American Peptide Society.

[33]  T. Kenakin,et al.  The ligand paradox between affinity and efficacy: can you be there and not make a difference? , 2002, Trends in pharmacological sciences.

[34]  I. Waelbroeck.  Kinetics versus equilibrium: the importance of GTP in GPCR activation. , 1999, Trends in pharmacological sciences.

[35]  B. Kobilka,et al.  Fluorescent labeling of purified beta 2 adrenergic receptor. Evidence for ligand-specific conformational changes. , 1995, The Journal of biological chemistry.

[36]  R A Mathies,et al.  The first step in vision: femtosecond isomerization of rhodopsin. , 1991, Science.

[37]  J. Ballesteros,et al.  Beta2 adrenergic receptor activation. Modulation of the proline kink in transmembrane 6 by a rotamer toggle switch. , 2002, The Journal of biological chemistry.

[38]  W. C. Swope,et al.  A computer simulation method for the calculation of equilibrium constants for the formation of physi , 1981 .

[39]  Eamonn F. Healy,et al.  Development and use of quantum mechanical molecular models. 76. AM1: a new general purpose quantum mechanical molecular model , 1985 .

[40]  Francesca Fanelli,et al.  Mutagenesis and modelling of the alpha(1b)-adrenergic receptor highlight the role of the helix 3/helix 6 interface in receptor activation. , 2002, Molecular pharmacology.

[41]  F. Guarnieri,et al.  Conformational memories and the endocannabinoid binding site at the cannabinoid CB1 receptor. , 2002, Journal of medicinal chemistry.

[42]  F Guarnieri,et al.  Agonist-induced Conformational Changes at the Cytoplasmic Side of Transmembrane Segment 6 in the β2 Adrenergic Receptor Mapped by Site-selective Fluorescent Labeling* , 2001, The Journal of Biological Chemistry.

[43]  K. Palczewski,et al.  Crystal Structure of Rhodopsin: A G‐Protein‐Coupled Receptor , 2002, Chembiochem : a European journal of chemical biology.

[44]  Klaus Schulten,et al.  Molecular dynamics investigation of primary photoinduced events in the activation of rhodopsin. , 2002, Biophysical journal.

[45]  Ursula Rothlisberger,et al.  Early steps of the intramolecular signal transduction in rhodopsin explored by molecular dynamics simulations. , 2002, Biochemistry.

[46]  S. O. Smith,et al.  The steric trigger in rhodopsin activation. , 1997, Journal of molecular biology.

[47]  H. Khorana,et al.  Requirement of Rigid-Body Motion of Transmembrane Helices for Light Activation of Rhodopsin , 1996, Science.

[48]  R. Razdan,et al.  Manipulation of the tetrahydrocannabinol side chain delineates agonists, partial agonists, and antagonists. , 1999, The Journal of pharmacology and experimental therapeutics.

[49]  Arieh Warshel,et al.  Bicycle-pedal model for the first step in the vision process , 1976, Nature.

[50]  W. C. Probst,et al.  Sequence alignment of the G-protein coupled receptor superfamily. , 1992, DNA and cell biology.

[51]  T. Kožár,et al.  Towards a better semiquantitative estimation of binding constants: molecular dynamics exploration of the conformational behavior of isolated sialyllactose and sialyllactose complexed with influenza A hemagglutinin , 1996 .

[52]  M. Sheves,et al.  The molecular origin of the inhibition of transducin activation in rhodopsin lacking the 9-methyl group of the retinal chromophore: a UV-Vis and FTIR spectroscopic study. , 2000, Biochemistry.

[53]  W. Gärtner,et al.  Signaling States of Rhodopsin , 2000, The Journal of Biological Chemistry.