Unexpected Route To Crystallization

Long-range electrostatic repulsion can drive crystallization in three-dimensional networks of like-charged peptide-based filaments, according to a study from Northwestern University (Science, DOI: 10.1126/science.1182340). The unprecedented crystallization mechanism could play a previously unrecognized role in forming cytoskeletal structures—the protein “scaffolding” in cells—and lead to advances in biomedical applications. Honggang Cui, Samuel I. Stupp, and coworkers report that a synthetic molecule made from a peptide sequence grafted to an alkyl chain spontaneously forms networks of cylindrical fibers. These filaments consist of a hydrocarbon core and peptide periphery that are roughly 10 nm in diameter and estimated to be at least tens of micrometers in length. In dilute solutions of about 1 wt % or higher, repulsion between negatively charged nanofibers causes the structures to crystallize spontaneously. In less concentrated solutions, deprotonation stimulated by X-rays triggers reversible crystallization, leading to ordered fiber bundles with interfiber separations of up to 320 Å. That distance is on the order of 10 times the range of values reported for cytoskeleton filaments and DNA strands, the team says.