Conformational changes of polypeptides in intense electric fields.

Abstract

AbstractEmploying a simple “all or none” statistical theory, a calculation is given of the phase diagram in electric field–temperature space for the helix–coil transition of a polypeptide with nonpolar residues but charged end groups. The principal results are (i) the transition field extrapolated to absolute zero is on the order of millions of volts per centimeter, (ii) the normal transition temperature of large molecules is predicted to be significantly affected by fields as low as 30,000 V/cm, and (iii) for temperatures just above the helix‐coil transition temperature, the application of a field to a large molecule causes an initial transition to the helix state and with a further isothermal increase of field the coil state returns. The theory is extended to the case of the unfolding of a globular protein in an electric field. The fields are somewhat lower than those for the helix‐coil transition and are always single‐valued at a given temperature. Lastly the effect of including the presence of charged residues is shown to decrease the estimated critical fields but keep them of the same order of magnitude as those given for the case of nonpolar residues.