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The conformation of the neurotransmitter acetylcholine bound to the fully functional nicotinic acetylcholine receptor embedded in its native membrane environment has been characterized by using frequency-selective recoupling solid-state NMR. Six dipolar couplings among five resolved [sup.13]C-labeled atoms of acetylcholine were measured. Bound acetylcholine adopts a bent conformation characterized with a quaternary ammonium-to-carbonyl distance of 5.1 [Angstrom]. In this conformation, and with its orientation constrained to that previously determined by us, the acetylcholine could be docked satisfactorily in the agonist pocket of the agonist-bound, but not the agonist-free, crystal structure of a soluble acetylcholine-binding protein from Lymnaea stagnali. The quaternary ammonium group of the acetylcholine was determined to be within 3.9 [Angstrom] of five aromatic residues and its acetyl group close to residues C187/188 of the principle and residue Ll12 of the complementary subunit. The observed >C=O chemical shift is consistent with H bonding to the nicotinic acetylcholine receptor residues [gamma]Y116 and [delta]T119 that are homologous to L112 in the soluble acetylcholine-binding protein. magic-angle spinning | membrane proteins | receptor pharmacology | solid-state NMR

The design principles of spider dragline silk, nature's high-performance fiber, are still largely unknown, in particular for the noncrystalline glycine-rich domains, which form the bulk of the material. Here we apply two-dimensional solid-state NMR to determine the distribution of the backbone torsion angles ([phi],[psi]) as well as the orientation of the polypeptide backbone toward the fiber at both the glycine and alanine residues. Instead of an 'amorphous matrix,' suggested earlier for the glycine-rich domains, these new data indicate that all domains in dragline silk have a preferred secondary structure and are strongly oriented, with the chains predominantly parallel to the fiber. As proposed previously, the alanine residues are predominantly found in [beta] sheet conformation. The glycine residues are partly incorporated into the [beta] sheets and otherwise form helical structures with an approximate 3-fold symmetry.

High-resolution magic-angle sample spinning experiments using total through-bond correlation spectroscopy and total through-space spectroscopy were carried out to examine the structure of organic solids. The results demonstrated the feasibility of probing both through-bond and through-space connectivities of calcium acetate monohydrate. However, both methods are limited to maximum distances of five angstrom and through-bond connectivities of up to three bonds only.

Nuclear magnetic resonance and power X-ray diffraction techniques have been used to study the crystal structure of anhydrous disodium hydrogen phosphate. NMR spectra reveal the superposition of several second-order quadrupolar centerband patterns and three inequivalent sodium sites consistent with a P2(sub1)/c space group and not the predicted P2(sub1)/m structure. Simultaneous double rotation experiments were further conducted to check number of sodium sites. The results of the test are presented.

Solid-state NMR and neutron diffraction technique are employed to analyze the alpha-base and beta-phase structures of methanol crystals. Temperature influences the alpha-phase methanol crystal structure. The relative orientation of two phases is calculated using a 13C chemical shielding tensor analysis. Hydrogen bonded chain rotates about its axis to induce the structure change. Labile methyl group is observed in the staggered conformation of beta-phase.