Nat. Neurosci. 10, 953–962 (2007); published online 22 July 2007; corrected after print 2 August 2007

In the version of this article initially published, the RCSB Protein Database accession code for the crystal structure was omitted. At the end of the first paragraph in the Methods section, the following sentence should have been included: “The coordinates for this crystal structure have been deposited in the RCSB Protein Database under the accession code 2QC1.” The error has been corrected in the HTML and PDF versions of the article.