Abstract
Life phenomena such as signal transduction and chemical balance in neural systems, are determined by proper and exquisitely timed changes in ion channel mediated conductance and/or membrane potential. The fundamental structure of ion channels is a bundle arrangement of the amphiphilic domains of a channel protein situated in a biological membrane. Stimulation induced high-order structural changes in the bundle resulting in the regulation of ion permeability through the membrane. We prepared a photo-responsive amphiphilic polypeptide composed of two amphiphilic α-helical polypeptides, poly [(γ-methyl L-glutamate) -co- (L-glutamic acid)] jointed by an azobenzene molecule as our photo-responsive ion channel model. We investigated the photo-induced structural and functional changes of this photo-responsive polypeptide within a lipid membrane. In the dark, the polypeptide formed a transmembrane bundle within the membrane by self-association causing the bundle to act as an ion permeable path. Photo-irradiation induced bending of the polypeptide via a trans-cis photo-isomerization of the azobenzene moiety. The photo-induced structural changes in the polypeptide resulted in a destablization of the transmembrane bundle, and the subsequent blocking of the ion permeable path. This behavior arose from the photo-induced denaturation of the amphiphilic character of the polypeptide. As a result, photo-induced structural changes of the polypeptide were observed to regulate transmembrane ion transport.
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