Large polymer molecules that self-assemble, generally adopt a globular, spherical shape, limiting their ability to form orderly aggregates. Polypeptides can adopt a spiral shape and act like cylindrical rods, but these tend to be insoluble in water. Any charge introduced into the side chains to promote solubility has led to the destabilization of the helix.

Jianjun Cheng and co-workers, University of Illinois, USA, have overcome this problem by elongating the side chains. This moved the charges farther from the backbone and produced water-soluble, ultra-stable α-helical polypeptides.

The polypeptides displayed remarkable stability even compared to non-charged helices. The helices were stable under changing environmental conditions such as temperature, pH, and in the presence of denaturing agents that would unwind most polypeptides.

The stable nature of the self-assembling polypeptides could lead to their use as agents for drug and gene delivery.

• Ionic polypeptides with unusual helical stability
  H. Lu, J. Wang, Y. Bai, J. W. Lang, S. Liu, Y. Lin, J. Cheng,
  Nat. Commun. 2011.
  DOI: 10.1038/ncomms1209