The transmembrane domains of the nicotinic acetylcholine receptor contain α-helical and β structures

Abstract

The transmembrane domain of the nicotinic acetylcholine receptor (nAChR) from Torpedo californica electric tissue contains both α-helical and β 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 α- helical 50%, β structure and turns 40%, random 10%. The α-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 β structures was observed. These findings contradict previous secondary structure models based on hydropathy plots alone.