Tarunendu Mapder, Lipika Adhya
Department of Engineering Physics, B.P. Poddar Institute of Management and Technology, Poddar Vihar, 137-VIP Road, Kolkata-700052, India.
The structure and functionality of voltage-gated ion channels and their neuronal and cardiac excitability in eukaryotes and some prokaryotes is reviewed1. The voltage-gated K+ ion channel of Aeropyrum pernix (KvAP) controls the flux of K+ ions through the cytosolic lipid membrane. This KvAP ion channel protein is a tetramer around a pore or passage of the ions. Accommodated within the 30Å lipid membrane each monomer is folded into six interlinked alpha helices (S1-S6), which are grouped into two functional domains: the voltage sensor domain (VSD(S1-S4)), and the pore domain (PD(S5-S6)). The response to the transmembrane voltage the conformation of the protein is dictated by the four dynamic transmembrane α-helices of the VSD. The spatial relationship among the transmembrane α-helices and the two domains within the ion channel protein affects the passage of ions through the pore domain. The H-bonded CO and NH groups of the polypeptide backbone of each monomer are oriented roughly parallel to the helix axis, therefore behaving like micro-dipoles. The aligned microdipoles along the alpha helix summate to form a macrodipole2. By using different methods3-4, the structure (fig.1) of the VSD of the KvAP voltage gated ion channel protein has been shown to consist of antiparallel helices with the N- and C-terminals of the adjacent α-helix remaining close to each other. Read more…