Transmuting alpha helices and beta sheets.

Protein architecture involves two main secondary structural classes: alpha helices and beta sheets. Some natural proteins alter their fold in response to changes in solution conditions or as a consequence of mutation. Here, we discuss recent attempts to induce such conformational changes by design: specifically, the motivation and success of efforts to change one protein fold into a different one in response to the 'Paracelsus Challenge'. The results of such efforts may provide a better understanding of the processes that underlie conformational plasticity in proteins.