Synthetic control of ion channels
Ion channels are an important group of proteins whose function entails large conformational motion. These molecules are pores embedded in the cell membrane which open and close on millisecond timescales, selectively allowing ionic currents to flow in and out of the cell. Specifically, voltage gated channels open and close in response to the polarization of the cell membrane; they are the molecular switches which sustain the action potential in nerve cells. The basic process is that these molecules undergo deformations in response to the large electric field across the membrane (of order 100 mV / 4 nm).
It is a matter of considerable interest to design new modes of control for ion channels: these can then be used in neuroscience research. Our approach is that such deformable molecules can always be controlled mechanically. Thus we design artificial control mechanisms based ultimately on exerting stresses on the molecule.
At left: Cell free electrophysiology setup for testing ion channel response.
One example is to add phosphorylation sites (by mutagenesis) to a voltage gated channel (the KvAP). The electric field due to the additional charges may bias the opening probability of the channel. With this construction we put the response of the channel under the control of a specific Kinase, adding a new layer of chemical control.
We explore a number of different designs for the artificial control of channels. The response of the modified channels is tested in a supported bilayer electrophysiology setup; the channels are expressed in bacteria and reconstituted in vesicles; the latter are fused to the artificial bilayer.
This work is in collaboration with the group of Elisha Moses at the Weizmann Institute in Israel: http://www.weizmann.ac.il/complex/EMoses//home.html.
At right, ion channel geometry with artificial phosphorylation sites. Opening and closing of the channel is controlled by the position of the α-helix (yellow) containing the positively charged Arginines; phosphorylation (addition of two negative charges) at the position shown may bias the position of this α-helix through electrostatic interactions, thus biasing the opening probability of the channel.
- A. Wang and G. Zocchi, "Artificial modulation of the gating behavior of a K+ channel in a KvAP-DNA chimera," PLoS ONE 6 (4), e18598 (2011).
- A. Ariyaratne and G. Zocchi, "Artificial phosphorylation sites modulate the activity of a voltage gated potassium channel," submitted (2014).