title: Secondary structure analysis of individual transmembrane segments of the nicotinic acetylcholine receptor by circular dichroism and Fourier transform infrared spectroscopy.
abstract: Circular dichroism (CD) and attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy are used to establish the secondary structure of peptides containing one or more transmembrane segments (M1-M4) of the Torpedo californica nicotinic acetylcholine receptor (AChR). Peptides containing the M2-M3 and M1-M2-M3 transmembrane segments of the AChR beta-subunit and the M4 segment of the alpha- and gamma-subunits were isolated from proteolytic digests of receptor subunits, purified, and reconstituted into lipid vesicles. For each peptide, an amide I vibrational frequency centered between 1650 and 1656 cm-1 and negative CD absorption bands at 208 and 222 nm indicate that the peptide is largely alpha-helical. In addition, the CD spectrum of a tryptic peptide of the alpha-subunit containing the M1 segment is also consistent with a largely alpha-helical structure. However, secondary structure analysis of the alpha-M1 CD spectrum indicates the presence of other structures, suggesting that the M1 segment may represent either a distorted alpha-helix, likely the consequence of several proline residues, or may not be entirely alpha-helical. Overall, these findings are consistent with studies that indicate that the transmembrane region of the AChR comprises predominantly, if not exclusively, membrane-spanning alpha-helices.
authors.affiliation: Department of Biology, University of California, Santa Cruz, California 95064, USA.
authors.forename: J
authors.initials: J
authors.lastname: Corbin
authors.forename: N
authors.initials: N
authors.lastname: Méthot
authors.forename: H H
authors.initials: HH
authors.lastname: Wang
authors.forename: J E
authors.initials: JE
authors.lastname: Baenziger
authors.forename: M P
authors.initials: MP
authors.lastname: Blanton
mesh_terms: D000818:Animals; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D006868:Hydrolysis; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000378:metabolism; D017550:Spectroscopy, Fourier Transform Infrared; D014101:Torpedo
chemical_list: D008565:Membrane Proteins; D011978:Receptors, Nicotinic