310 helices in channels and other membrane proteins

Structures of three potassium channels of the six-transmembrane (TM) helix type, a ligand-gated channel, and two voltage-gated channels were solved recently by x-ray crystallography ([Long et al., 2005a][1],[b][2], [2007][3]; [Clayton et al., 2008][4]). In all three channel structures, the fourth TM