Nat. Chem. Biol. 6, 630 (2010) 10.1038/nchembio0810-630b; published online 19 July 2010; corrected after print 18 August 2010

In the Erratum initially published, the correction date was stated as 17 June 2010, when the correct date should have been 19 July 2010. The error has been corrected in the HTML and PDF versions of the Erratum.