VOLTAGE-DEPENDENT GATING OF AN ASYMMETRIC GRAMICIDIN CHANNEL

In an effort to understand the molecular mechanisms of voltage activat ion of ion channels, we have chosen a system of known structure and ex amined the properties of heterodimeric channels formed between [Val(1) ]gramicidin A ([Val(1)]gA) and [F(6)Val(1)]gramicidin A ([F(6)Val(1)]g A). Gramicidin channels are usually not voltage-dependent; but the int roduction of a single symmetrybreaking dipolar F(6)Val(1) residue into a ([Val(1)]gA)(2) dimer to form the [F(6)Val(1)]gA/[Val(1)]gA heterod imer induces voltage-dependent transitions between two conducting stat es: a high-conductance state and a zero conductance (closed) state. Th e distribution between these states varies as a function of the applie d potential but is not dependent on the nature of the permeant ion (H or Cs+). The permeating ions do not seem to contribute to the apparen t gating charge.