Summary
SCF
(Skp1-Cullin-F-box)
ubiquitin ligases comprise several dozen modular enzymes that have diverse roles
in biological regulation. SCF enzymes share a common catalytic core containing
Cul1•Rbx1, which is directed towards different substrates by a variable
substrate receptor (SR) module comprising one of 69 F-box proteins bound to
Skp1. Despite the broad cellular impact of SCF enzymes, important questions
remain about the architecture and regulation of the SCF repertoire, including
whether SRs compete for Cul1, and if so, how this competition is managed. Here,
we devise methods that preserve the in vivo assemblages of SCF
complexes, and apply quantitative mass spectrometry to perform a census of these
complexes (the ‘SCFome’) in various states. We show that Nedd8
conjugation and the SR exchange factor Cand1 have a profound effect on shaping
the SCFome. Together, these factors enable rapid remodeling of SCF complexes to
promote biased assembly of SR modules bound to substrate.