| An exciting new field, physical organic chemistry on the brain, is emerging as a major frontier at the interface between chemistry and neurobiology. The present work addresses some of the fundamental structural and mechanistic questions about the nicotinic acetylcholine receptor (nAChR) by using a wide spectrum of methods, ranging from ab initio quantum mechanical calculation and chemical synthesis to molecular biology and electrophysiology.; We present convincing mutagenesis data in Chapter 2 to support a crucial role for cation-π interactions in acetylcholine (ACh) binding to the nAChF, confirming the proposal by Dougherty and Stauffer eight years ago. We found that at one and only one site—αTrp 149—EC50 correlates strongly with the cation-π binding ability of the aromatic sidechain. This is clear evidence that the αTrp 149 sidechain is in van der Waals contact with the quaternary ammonium group of ACh, providing the most precise structural information to date on this complex, multisubunit protein. In Chapter 3, we report supporting evidence for this model by incorporating Tyr-O3Q, an amino acid with a quaternary ammonium group, at α 149 and evaluating the behavior of the constitutively active nAChR molecules. This also opens the possibility for much broader exploration of the tethered agonist approach in studying ion channels.; In Chapter 4, we describe findings of remote couplings (over a distance of some 50 Å) in receptor activation between acidic residues near the agonist binding site and hydrophobic leucines at the 9′ position in the M2 pore region. The βLeu9′ couples most strongly to these acidic residues. In addition, we document studies aimed to probe a putative hydrogen bond at subunit interfaces.; Methods in electrophysiology, molecular biology, and synthesis of various amino acids are summarized in Chapter 5. In Chapter 6, we discuss studies to explore the cation-π interaction in superamolecular systems. The design and synthesis of a potential alkali metal ion host are described. |
