Chain stiffness of elastin-like polypeptides.

The hydrodynamic radii of a series of genetically engineered monodisperse elastin like polypeptides (ELP) was determined by dynamic light scattering in aqueous solution as function of molar mass. Utilizing the known theoretical expression for the hydrodynamic radius of wormlike chains, the Kuhn statistical segment length was determined to be = 2.1 nm, assuming that the length of the peptide repeat unit was = 0.365 nm, a value derived for a coiled conformation of ELP. The resulting chain stiffness is significantly larger than previously reported by force-distance curve analysis ( < 0.4 nm). The possible occurrence of superstructures, such as hairpins or helices, would reduce the contour length of the ELP, further increasing . Accordingly, the value = 2.1 nm reported here represents a lower limit of the chain stiffness for ELP.