Autoantibodies and monoclonal antibodies in the purification and molecular characterization of neurotransmitter receptors

Molecular receptors and their potential for artificial transduction

The thesis is presented that molecular receptor physical chemistry offers an interesting model for the design of biosensors with respect to chemical recognition and transduction. In order to appreciate the desirable features of this system and the inherent difficulties, the structures and binding state energetics of molecular receptors are considered via a direct comparison with enzyme chemistry. Detailed analyses of the candidate species nicotinic and beta-adrenergic receptors are provided to illustrate the complexity of molecular receptor binding properties. A revised ternary-complex model, which combines enzymatic and receptor energetics, is proposed to explain the free-energy changes which drive ligand-binding reactions of coupled systems. Throughout this discussion the relevance of the various arguments to applications in biosensor development is highlighted. Finally, a brief appraisal of attempts to produce devices ready for marriage to molecular receptor material is presented.

Reconstitution of solubilized atrial cholinergic muscarinic receptors in liposomes

The reconstitution of solubilized bovine atrial cholinergic muscarinic receptor into liposomes made of exogenous lipids has been achieved by polyethyleneglycol precipitation. Of the different lipid mixtures used, soybean lecithins were shown to be the best on the basis of receptor recovery. The receptor reconstituted into soybean lecithins liposomes exhibited ligand binding properties very similar to those of the native receptor. The dissociation constant of [3H]-N-methyl-scopolamine ([3H]NMS) was 0.46 and 0.30 nM as determined by equilibrium and kinetics experiments respectively. The potency of a range of muscarinic ligands in displacing [3H]NMS binding was atropine greater than methyl-atropine greater than scopolamine greater than pirenzepine oxotremorine greater than gallamine greater than carbamylcholine greater than pilocarpine bethanechol. The Hill slopes of the displacement curves were near 1 for the antagonists and smaller than 1 for the agonists and for gallamine. The agonist binding may be modulated by guanine nucleotides. These results indicate that soybean lecithins fulfill the lipid requirements for the reconstitution of the atrial muscarinic receptor.

Monoclonal antibodies detect the conservation of muscarinic cholinergic receptor structure from Drosophila to human brain and detect possible structural homology with alpha 1-adrenergic receptors

Muscarinic cholinergic receptors isolated from Drosophila heads, rat and human brain, dog heart, and monkey ciliary muscle were examined for structural similarities/differences by utilizing isoelectric focusing, sodium dodecyl sulfate/polyacrylamide gel electrophoresis, and monoclonal antibody crossreactivity. Muscarinic receptors were affinity labeled with [3H]propylbenzilylcholine mustard and subjected to isoelectric focusing. Muscarinic receptors from each species focused with an isoelectric point of 5.9. The same proteins all migrated with an apparent molecular mass of 80,000 daltons on sodium dodecyl sulfate gels. Six hybridomas secreting monoclonal antibodies specific for muscarinic receptors were developed by using purified rat brain muscarinic receptors as the antigen. The six different monoclonal antibodies immunoprecipitated muscarinic receptors from all tissues and species tested, including human and Drosophila brains, with equal efficacy. These data indicate that muscarinic receptors are highly conserved over a considerable evolutionary period. One of the six muscarinic receptor monoclonal antibodies also immunoprecipitated rat liver alpha 1-adrenergic receptors. Furthermore, two out of five monoclonal antibodies raised against alpha 1-receptors immunoprecipitated muscarinic receptors. These data suggest that some degree of structural homology exists between muscarinic cholinergic receptors and alpha 1-adrenergic receptors.