Preparation of silk-like fibers designed by self-assembled ionic polypeptides

Natural protein fibers, such as silk, having high-performance characteristics have been important materials in biopolymer research. This article reports the development of a silk-like extensive poly(alpha,L-amino acid) fiber inspired by self- assembly of polypeptides in living systems. Electrostatic interaction was employed as the driving force for building the fiber, and we succeeded in spinning the fiber from an aqueous solution interface between poly(alpha,L-lysine) (PPL) and poly(alpha,L-glutamic acid) (PLG). When the PLL/PLG fiber was formed, the conformations of PLL and PLG were changed from random to beta-structures. A remarkable feature of the PLL/PLG fiber resulted in a change from an extensible fiber to a rigid and strong fiber. These features depend on the molecular conformation and the deviation in the amino acid composition of the PLL/PLG fibers. This concept and the poly(alpha,L-amino acid) fibers themselved allow the production of new protein fobers and aid the development of the science of protein folding as well as giving insight into the noncovalent interactions involved in self-assembly.