Structural fluctuations between two conformational states of a transmembrane helical peptide are related to its channel‐forming properties in planar lipid membranes

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Abstract
Putative transmembrane helices of membrane proteins in general and channel proteins in particular often contain proline residues which may induce a bend into an otherwise regular helical structure. Here we show by fluorescence‐energy‐transfer measurements and molecular‐dynamics calculations that, in the case of synthetic bilayer‐spanning helical polypeptides, a proline‐induced bend in a helix acts as a flexible element mediating rigid body motions of the helical segments. Most important, such structural fluctuations in the transmembrane helices seem to play a functional role in the formation of ionic channels in planar lipid bilayers and biological membranes.