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Identification of essential cannabinoid-binding domains: structural insights into early dynamic events in receptor activation.

ABSTRACT: The classical cannabinoid agonist HU210, a structural analog of (-)-?(9)-tetrahydrocannabinol, binds to brain cannabinoid (CB1) receptors and activates signal transduction pathways. To date, an exact molecular description of the CB1 receptor is not yet available. Utilizing the minor binding pocket of the CB1 receptor as the primary ligand interaction site, we explored HU210 binding using lipid bilayer molecular dynamics (MD) simulations. Among the potential ligand contact residues, we identified residues Phe-174(2.61), Phe-177(2.64), Leu-193(3.29), and Met-363(6.55) as being critical for HU210 binding by mutational analysis. Using these residues to guide the simulations, we determined essential cannabinoid-binding domains in the CB1 receptor, including the highly sought after hydrophobic pocket important for the binding of the C3 alkyl chain of classical and nonclassical cannabinoids. Analyzing the simulations of the HU210-CB1 receptor complex, the CP55940-CB1 receptor complex, and the (-)-?(9)-tetrahydrocannabinol-CB1 receptor complex, we found that the positioning of the C3 alkyl chain and the aromatic stacking between Trp-356(6.48) and Trp-279(5.43) is crucial for the Trp-356(6.48) rotamer change toward receptor activation through the rigid-body movement of H6. The functional data for the mutant receptors demonstrated reductions in potency for G protein activation similar to the reductions seen in ligand binding affinity for HU210.

SUBMITTER: Shim JY

PROVIDER: S-EPMC3190901 | biostudies-literature | 2011 Sep

REPOSITORIES: biostudies-literature

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Identification of essential cannabinoid-binding domains: structural insights into early dynamic events in receptor activation.

Shim Joong-Youn JY Bertalovitz Alexander C AC Kendall Debra A DA

The Journal of biological chemistry 20110727 38

The classical cannabinoid agonist HU210, a structural analog of (-)-Δ(9)-tetrahydrocannabinol, binds to brain cannabinoid (CB1) receptors and activates signal transduction pathways. To date, an exact molecular description of the CB1 receptor is not yet available. Utilizing the minor binding pocket of the CB1 receptor as the primary ligand interaction site, we explored HU210 binding using lipid bilayer molecular dynamics (MD) simulations. Among the potential ligand contact residues, we identified ...[more]

PMID: 21795705

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Project description:[Structure: see text]. FHA domains are protein modules that switch signals in diverse biological pathways by monitoring the phosphorylation of threonine residues of target proteins. As part of the effort to gain insight into cellular avoidance of cancer, FHA domains involved in the cellular response to DNA damage have been especially well-characterized. The complete protein where the FHA domain resides and the interaction partners determine the nature of the signaling. Thus, a key biochemical question is how do FHA domains pick out their partners from among thousands of alternatives in the cell? This Account discusses the structure, affinity, and specificity of FHA domains and the formation of their functional structure. Although FHA domains share sequence identity at only five loop residues, they all fold into a beta-sandwich of two beta-sheets. The conserved arginine and serine of the recognition loops recognize the phosphorylation of the threonine targeted. Side chains emanating from loops that join beta-strand 4 with 5, 6 with 7, or 10 with 11 make specific contacts with amino acids of the ligand that tailor sequence preferences. Many FHA domains choose a partner in extended conformation, somewhat according to the residue three after the phosphothreonine in sequence (pT + 3 position). One group of FHA domains chooses a short carboxylate-containing side chain at pT + 3. Another group chooses a long, branched aliphatic side chain. A third group prefers other hydrophobic or uncharged polar side chains at pT + 3. However, another FHA domain instead chooses on the basis of pT - 2, pT - 3, and pT + 1 positions. An FHA domain from a marker of human cancer instead chooses a much longer protein fragment that adds a beta-strand to its beta-sheet and that presents hydrophobic residues from a novel helix to the usual recognition surface. This novel recognition site and more remote sites for the binding of other types of protein partners were predicted for the entire family of FHA domains by a bioinformatics approach. The phosphopeptide-dependent dynamics of an FHA domain, SH2 domain, and PTB domain suggest a common theme: rigid, preformed binding surfaces support van der Waals contacts that provide favorable binding enthalpy. Despite the lack of pronounced conformational changes in FHA domains linked to binding events, more subtle adjustments may be possible. In the one FHA domain tested, phosphothreonine peptide binding is accompanied by increased flexibility just outside the binding site and increased rigidity across the beta-sandwich. The folding of the same FHA domain progresses through near-native intermediates that stabilize the recognition loops in the center of the phosphoprotein-binding surface; this may promote rigidity in the interface and affinity for targets phosphorylated on threonine.

Dataset Information

Identification of essential cannabinoid-binding domains: structural insights into early dynamic events in receptor activation.

Publications

Identification of essential cannabinoid-binding domains: structural insights into early dynamic events in receptor activation.

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