Nat. Struct. Mol. Biol. 16, 833–839 (2009); published online 2 August 2009; corrected after print 22 September 2009

In the version of this article initially published, the Grp1 structure described in Figure 3c was incorrectly labeled Grb1. The corrected figure panel is shown below. The error has been corrected in the HTML and PDF versions of the article.