We thank J. Lei and the staff at the Tsinghua University Branch of China National Center for Protein Sciences Beijing for providing facility support. This work was supported by the Chinese MOST (2017YFA0102900), the National Natural Science Foundation of China (31825016, 31570731, 31630046) to Z.C. and (11834018) to Ming Li.

Reviewer information

Nature thanks Beat Fierz and the other anonymous reviewer(s) for their contribution to the peer review of this work.