Reevaluation of hydropathy profiles of voltage-gated ionic channels.

A reevaluation of the secondary structure of Na, Ca and K channel proteins led to the following results. Only three segments (S1, S5 and S6) of each repeat are sufficiently hydrophobic to be predicted as transmembrane helices, if a window of 19 amino acids is used. Some of the S2 and S3 segments show higher hydrophobic values when calculated with the window of 9 amino acids and can be predicted as short helices. S4 segments are strongly hydrophilic and cannot be predicted as transmembrane helices. Some of the S2, S3 and S4 segments have an amphipathic character; however, these helices do not span a membrane. A model is proposed where 12 hydrophobic transmembrane helices surround 12 shorter helices, forming a hydrophilic pore. In addition, a unique pattern for S4 segments of voltage-gated channel proteins is defined.