Proline 411 biases the conformation of the intrinsically disordered plant UVR8 photoreceptor C27 domain altering the functional properties of the peptide

Abstract

UVR8 (UV RESISTANCE LOCUS 8) is a UV-B photoreceptor responsible for initiating UV-B signalling in plants. UVR8 is a homodimer in its signalling inactive form. Upon absorption of UV radiation, the protein monomerizes into its photoactivated state. In the monomeric form, UVR8 binds the E3 ubiquitin ligase COP1 (CONSTITUTIVELY PHOTOMORPHOGENIC 1), triggering subsequent UV-B-dependent photomorphogenic development in plants. Recent in vivo experiments have shown that the UVR8 C-terminal region (aa 397–423; UVR8C27) alone is sufficient to regulate the activity of COP1. In this work, CD spectroscopy and NMR experiments showed that the UVR8C27 domain was non-structured but gained secondary structure at higher temperatures leading to increased order. Bias-exchange metadynamics simulations were also performed to evaluate the free energy landscape of UVR8C27. An inverted free energy landscape was revealed, with a disordered structure in the global energy minimum. Flanking the global energy minimum, more structured states were found at higher energies. Furthermore, stabilization of the low energy disordered state was attributed to a proline residue, P411, as evident from P411A mutant data. P411 is also a key residue in UVR8 binding to COP1. UVR8C27 is therefore structurally competent to function as a molecular switch for interaction of UVR8 with different binding partners since at higher free energies different structural conformations are being induced in this peptide. P411 has a key role for this function.

Plant photoreceptors and their signaling components compete for binding to the ubiquitin ligase COP1 using their VP-peptide motifs

“…For both types of photoreceptors, interaction through a linear VP-peptide motif and a folded, light-regulated interaction domain leads to cooperative, high-affinity binding of the activated photoreceptor to COP1. We propose that in response to UV-B light, UVR8 dimers monomerize, exposing a new interaction surface that binds to the COP1 WD40 domain and releases the UVR8 C-terminal VP motif from structural restraints that prevent its interaction with COP1 in the absence of UV-B (Yin et al, 2015;Heilmann et al, 2016;Wu et al, 2019;Camacho et al, 2019). Similarly, the VP motif in the CCT domain of cryptochromes may become exposed and available for interaction upon blue-light activation of the photoreceptor (Müller and Bouly, 2015;Wang et al, 2018).…”

Plant photoreceptors and their signaling components compete for COP 1 binding via VP peptide motifs

“…For both types of photoreceptors, interaction through a linear VP peptide motif and a folded, light‐regulated interaction domain leads to cooperative, high‐affinity binding of the activated photoreceptor to COP1. We propose that in response to UV‐B light, UVR8 dimers monomerize, exposing a new interaction surface that binds to the COP1 WD40 domain and releases the UVR8 C‐terminal VP motif from structural restraints that prevent its interaction with COP1 in the absence of UV‐B (Yin et al , ; Heilmann et al , ; Camacho et al , ; Wu et al , ). Similarly, the VP motif in the CCT domain of cryptochromes may become exposed and available for interaction upon blue‐light activation of the photoreceptor (Müller & Bouly, ; Wang et al , ).…”

RUP2 facilitates UVR8 redimerization via two interfaces

“…UVR8 comprises two distinct domains: an N-terminal UV-B sensing core domain (residues 12–381) and a flexible C-terminal domain encompassing the C27 (residues 397–423) and C17 (residues 424–440) subregions ( Christie et al., 2012 ; Cloix et al., 2012 ; Wu et al., 2012 ; Yin et al., 2015 ; Lin et al., 2020 ). The C27 subregion contains a Val-Pro (VP) motif responsible for binding to the COP1/SPA complex ( Holm et al., 2001 ; Yin et al., 2015 ; Lau et al., 2019 ; Wu et al., 2019 ; Wang et al., 2022 ) ( Figure 1 A). In the ground state, UVR8 forms a bottom-to-bottom symmetric dimer via a network of salt bridges mediated by two surface patches of complementary charged residues in the core domains ( Christie et al., 2012 ; Wu et al., 2012 ).…”