The transmembrane domains of the nicotinic acetylcholine receptor contain alpha-helical and beta structures.

Abstract

The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) from Torpedo californica electric tissue contains both alpha‐helical and beta structures. The secondary structure was investigated by Fourier transform infrared (FTIR) spectroscopy after the extramembrane moieties of the protein from the extracellular and intracellular sides of the membrane were removed by proteolysis using proteinase K. The secondary structure composition of this membrane structure was: alpha‐helical 50%, beta structure and turns 40%, random 10%. The alpha‐helices are shown to be oriented with respect to the membrane plane in a way allowing them to span the membrane, while no unidirectional structure for the beta structures was observed. These findings contradict previous secondary structure models based on hydropathy plots alone.

Structure and Function of the Glycine Receptor and Related Nicotinicoid Receptors

“…Although M2 and M4 appear to be transmembrane ␣-helices, some experimental evidence has raised questions regarding whether every transmembrane segment is a requisite helix. CD data of reconstituted GlyR (26) and Fourier transform infrared spectroscopic studies showing that the nAChR transmembrane domains contain both ␣-helices and ␤ structure (27) are among the first direct spectroscopic evidence that the 4 TM model may be erroneous. Studies of the GlyR utilizing limited proteolysis coupled with mass spectroscopy (MS) (28) and chemical labeling studies coupled with MS (29) have also provided direct evidence that contradicts aspects of the 4 TM model.…”

Transporters of Nucleotide Sugars, Atp, and Nucleotide Sulfate in the Endoplasmic Reticulum and Golgi Apparatus

“…The periodicity of photolabeling with 125 I-TID [3-trifluoromethyl-3-(m-[ 125 I]iodophenyl)diazirine] may indicate whether a transmembrane segment is exposed to the lipid environment and whether it has alpha-helical secondary structure. Fourier-transformed infrared spectroscopy may also give insight into the secondary structure of membrane proteins, and measurements of linear dichroism may be used to investigate the orientation of secondary-structure elements with respect to the membrane (106).…”

Characterization of the 70 kDa polypeptide of the Na/Ca exchanger

“…The sample was then diluted in 1 M NaCl\0.5 mM Mops (pH 7.4 at 22 mC) and vortex-mixed for 2-3 min to eliminate the protease, digested peptides and non-membrane-associated digestion products [22,23]. The increase in the ionic strength of the solution (to 1 M NaCl) also decreased possible peptide-lipid interactions.…”