生体膜のイオンチャネルの構造と機能

抄録

The hydrophobic environment of the lipid membrane bilayer is virtually impermeable to ions in aqueous solution. Protein channels permit the rapid flux of ions across membranes. Ion channels have a common structural motif, the transmembrane α-helix. In its most energetically favorable form the protein must be configured such that its most hydrophilic residues point toward the aqueous channel and its hydrophobic residues face the lipid bilayer. Voltage-gated ion channel for Na⁺ is constracted from a single large polypeptide chain. The polypeptide includes four internally homologous domains I-IV, each containing six hydrophobic membrane-spanning regions, S1-S6, that probably correspond to α-helices. These four interconnected domains are thought to arrange as a tetramer surrounding the voltage-gated ion channel. S4 is thought to fuction as the actual voltage sensor of depolarization that causes a conformational change to open the channel pore. A small pore size and the biochemistry of the pore lining conspire to determine the ion selectivity of a particular type of channel.