. Author manuscript; available in PMC: 2016 Oct 18.
Published in final edited form as: Nat Chem. 2016 Apr 18;8(6):556–562. doi: 10.1038/nchem.2493
Users may view, print, copy, and download text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms
Reprints and permissions information is available online at www.nature.com/reprints