THE TRANSMEMBRANE DOMAINS OF THE NICOTINIC ACETYLCHOLINE-RECEPTOR CONTAIN ALPHA-HELICAL AND BETA-STRUCTURES

The transmembrane domain of the nicotinic acetylcholine receptor (nACh R) from Torpedo californica electric tissue contains both alpha-helica l and beta structures. The secondary structure was investigated by Fou rier transform infrared (FTIR) spectroscopy after the extramembrane mo ieties of the protein from the extracellular and intracellular sides o f the membrane were removed by proteolysis using proteinase K. The sec ondary structure composition of this membrane structure was: alpha-hel ical 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 a llowing them to span the membrane, while no unidirectional structure f or the beta structures was observed. These findings contradict previou s secondary structure models based on hydropathy plots alone.