R-helix Movement during Common Gating Affects Cl Binding in the CLC-0 Channel Pore

Abstract

Common (slow) gating of CLC-0 generates long silent periods in single-channel recordings and contributes significantly to regulation of Cl- permeation. Our previous study suggests that movement of the pore-forming R-helix is directly coupled to common gating. We now report that R-helix movement appears to directly interfere with Cl- binding in the pore. Binding of Cl- to the pore facilitates common gate opening, while removing Cl- slows down common gate opening. Mutations in R-helix that strongly affect common gating also appreciably shift the Cl- dependence of channel open rate, apparently by altering the binding affinity of Cl- in the pore. In this way, the common gating mechanism of CLC-0 is reminiscent of the fast gating, which also involves the control of chloride binding to the pore.