. Author manuscript; available in PMC: 2016 Jun 14.
Published in final edited form as: Nat Chem Biol. 2015 Dec 14;12(2):117–123. doi: 10.1038/nchembio.1981
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