Probing The Length Of The Gating Pore In K-channels By Mutations Along The Spiral Arginine Thread of S4

Abstract

Voltage-gated ion channels sense voltage by moving arginine residues located in the S4 segment across the membrane electric field. According to the helical screw model these arginines, which gates the channel, move through a defined molecular gating pore. Tombola et al., 2007 were able to show a leak current (omega current) when the first arginine R1 was substituted with a smaller amino acid. For Nav1.2 channels, Sokolov et al., 2005 reported that the leak current only appears when the two outermost arginines are replaced by glutamine. In the present study, we probe the length of the gating pore and ask for the minimum number of amino acids which should occupy the gating pore in order to block it. To check that, the short Alanine 359 which lies next to R1S (362) was replaced by arginine. We expected that A359R will mimic the function of R1 and block or at least diminish the omega current. Approximately 80% of the omega current was blocked compared to the classical R1S construct. The mutation of the second arginine R2 to serine (R1,R2S,R3) also shows a little omega current. In both of these mutations ,(A359R, R1S,R2) (R1,R2S,R3), two long amino acids are separated by one short amino acid. However, the construct with the double mutation (R1, R2S, R3S, R4) produced a large omega current. These findings suggest that the length of the narrow part of the gating pore is just about two inter-arginine distances.