We thank F. Sicheri, J. Fontana, A. Berry, C. Simon, I. Nissim, F. Sobott, J. Cockburn and A. Moloney for useful discussions, and R. Thompson, A. Gordon, M. Iadanza and M. Fuller for technical support. This work was supported by a Sir Henry Dale Fellowship (Wellcome Trust and the Royal Society; 200523/Z/16/Z) to E.Z., MRC MC_PC-16050 grant to E.Z. and F.D.G., NIH R01 CA138835 and a Lupus Research Alliance Target Identification in Lupus grant to R.A.G. and J.M.S., a BBSRC (BB/L021250/1) grant to N.A.R., a BBSRC TDRF grant BB/N021703/1 and North West Cancer Research grants CR1088, CR1097 to P.A.E., and a Polish National Science Centre grant (2014/15/B/NZ1/03359) to K.P. The University of Leeds mass spectrometry facility is supported by BBSRC (BB/E012558/1) and Wellcome Trust (208385/Z/17/Z) grants. The Astbury cryo-EM facility is funded by a University of Leeds ABSL award and Wellcome Trust grant 108466/Z/15/Z.

Reviewer information

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