A significant challenge in designing self-assembled molecular systems is the development of reliable and predictable methods to control the function of these assemblies.  Here, we evaluate the effect of charged groups conjugated to gramicidin A (gA, an ion channel-forming peptide) on the lifetime of these self-assembled ionic pores.  We demonstrate that charged groups attached to the C-terminus of gA can dramatically affect the lifetime (t) and conductance (?) of the channel in bilayers of phosphatidylcholine lipids.  Since t and ? dictate ion flux through gA pores, they represent the most important functional parameters of these self-assembled structures.  Interestingly, we observed opposing trends for the difference in t and ? of positively versus negatively charged derivatives of gA as a function of the ionic strength in the electrolyte.  This contrasting behavior made it possible to control the functional properties (t and ?) of gA pores with light of different wavelengths by introducing a photoactive spiropyran group, which can be switched dynamically between a positive and a neutral state. The methods reported here for using charge to influence the function of gramicidin channels in membranes represents a step towards achieving the level of control between structure and function of self-assembled structures that is typically observed only in nature.

Controlling trans-membrane ion conductance through gramicidin-based nanopores

243rd National Meeting (2012)

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