Correction to: Nature Structural and Molecular Biology https://doi.org/10.1038/s41594-019-0344-5, published online 2 December 2019.

In the version of this article initially published, in Fig. 6b, top left panel, the β-sheet was labeled as a “Three-stranded bridging sheet.” The correct label is “Four-stranded bridging sheet.” The error has been corrected in the HTML and PDF versions of the article.