. Author manuscript; available in PMC: 2015 Jan 1.
Published in final edited form as: Nat Chem. 2014 Jun 1;6(7):635–643. doi: 10.1038/nchem.1963
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