Native Mass Spectrometry Reveals the Conformational Diversity of the UVR8 Photoreceptor

UVR8 is a plant photoreceptor protein that regulates photomorphogenic and protective responsesto UV light. The inactive, homodimeric state absorbs UV-B light resulting in dissociation into monomers,which are considered to be the active state and comprise a b-propeller core domain and intrinsicallydisordered N- and C-terminal tails. The C-terminus is required for functional binding to signalling partnerCOP1. To date, however, structural studies have only been conducted with the core domain where theterminal tails have been truncated. Here, we report structural investigations of full-length UVR8 using nativeion mobility mass spectrometry adapted for photo-activation. We show that, whilst truncated UVR8 photoconvertsfrom a single conformation of dimers to a single monomer conformation, the full-length proteinexists in numerous conformational families. The full-length dimer adopts both a compact state and anextended state where the C-terminus is primed for activation. In the monomer the extended C-terminusdestabilises the core domain to produce highly extended yet stable conformations, which we propose arethe fully active states that bind COP1. Our results reveal the conformational diversity of full-length UVR8. Wealso demonstrate the potential power of native mass spectrometry to probe functionally important structuraldynamics of photoreceptor proteins throughout nature.