SODIUM DODECYL SULFATE-INDUCED AND CARBAMYLCHOLINE-INDUCED CHANGES INCIRCULAR-DICHROISM SPECTRA OF ACETYLCHOLINE-RECEPTOR SYNTHETIC PEPTIDES

The effect of sodium dodecyl sulfate (SDS) on the conformation of acet ylcholine receptor a-subunit synthetic peptides was investigated by ci rcular dichroism. In the presence of SDS (0.01-0.02%), the affinity of a 173-204 32 residue peptide and a 172-227 56 residue peptide for the competitive antagonist alpha-bungarotoxin increases about 10-fold to the nanomolar range. Circular dichroism spectroscopy of these peptides revealed significant changes in the secondary structure of the peptid es in the presence of SDS at concentrations below the critical micelle concentration. It is concluded that SDS induces a conformation of the peptides that is conducive to high affinity binding. Carbamylcholine, an acetylcholine analog, produced small but significant changes in th e spectrum of the 173-204 peptide. This change could be the result of agonist-induced conformational changes in this region of the acetylcho line receptor alpha-subunit or to changes in the asymmetric environmen ts of aromatic chromophores in the binding site. These studies demonst rate that synthetic peptides alone are capable of retaining significan t functional activity and contain significant secondary structure.