Nat. Chem. Biol. 9, 485–487 (2013); published online 23 June 2013; corrected after print 19 December 2013

In the version of this article initially published, the Protein Data Bank codes for the P450 and P411 constructs were inadvertently switched. Accession code 4H23 actually corresponds to the P411 structure, and 4H24 corresponds to the P450 structure. The error has been corrected in the HTML and PDF versions of the article.