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Uvr8

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Uvr8

UVB-resistance protein UVR8
Crystal structure of UVB-resistance protein UVR8.[1]
Identifiers
Organism
Symbol UVR8
Entrez 836506
PDB 4DNW More structures
RefSeq (mRNA) NM_125781
RefSeq (Prot) NP_201191
UniProt Q9XHD7
Other data
Chromosome 5: 25.55 - 25.56 Mb

UV-B resistance 8 (UVR8) also known as ultraviolet-B receptor UVR8 is an UV-Bsensing protein found in plants and possibly other sources.[2] It is responsible for sensing ultraviolet light in the range 280-315 nm and initiating the plant stress response. UVR8 was first identified as a crucial mediator of a plant's repsonse to UV-B in Arabidopsis thaliana containing a mutation in this protein. This plant was found to have a hypersensitivity to UV-B[3] which damages DNA. UVR8 is thought to be a unique photoreceptor as it doesn't contain a prosthetic chromophore but its light-sensing ability is intrinsic to the molecule. Tryptophan (Trp) residue 285 has been suggested to act the UV-B sensor, while other Trp residues have been also seen to be involved (Trp233 > Trp337 > Trp94).[2]

Structure

UVR8 is a β-propeller protein with 7 blade-shaped β-sheets. It shares sequence homology with mammalian proteins involved in regulating chromatin condensation, for example the human RCC1 gene product. In the dark state, UVR8 forms a homodimer that is localized in the cytosol, but UV-B illumination induces the dissociation of UVR8 dimer to its respective monomers and translocation to the nucleus occurs.[4] The dimer is held together via a complex salt bridge network.[2]

Mechanism

Upon UV-B irradiation, light is absorbed by one or more Trp residues which are situated adjacent to Arg residues which form salt bridges across the dimer interface. It is thought that this light absorption induces the disruption of the salt-bridges and thus leads to the molecule's monomerization.[2][5] Following monomerization, UVR8 accumulates in the nucleus where it interacts with a protein called constitutively photomorphogenic 1 (COP1). COP1 is known to act as an E3 Ubiquitin ligase that targets key transcription factors for ubiquitination and proteasome-mediated degradation. However, in the case of UVR8, it has been shown to act as a positive regulator of UVR8-mediated UV-B signalling.[6] Upon UV-B illumination, UVR8 interacts via a C-terminal 27 amino acid region with the WD40 domain of COP1 in the nucleus,[7] which triggers the induction of a elongated hypocotyl5 (HY5)- a key transcription factor for several UV-B responsive genes- and overall results in UV-B acclimation.[8]

References

  1. ^ ; Wu D, Hu Q, Yan Z, Chen W, Yan C, Huang X, Zhang J, Yang P, Deng H, Wang J, Deng X, Shi Y (April 2012). "Structural basis of ultraviolet-B perception by UVR8". Nature 484 (7393): 214–9.  
  2. ^ a b c d Christie JM, Arvai AS, Baxter KJ, Heilmann M, Pratt AJ, O'Hara A, Kelly SM, Hothorn M, Smith BO, Hitomi K, Jenkins GI, Getzoff ED (February 2012). "Plant UVR8 Photoreceptor Senses UV-B by Tryptophan-Mediated Disruption of Cross-Dimer Salt Bridges". Science 335 (6075): 1492–6.  
  3. ^ Kliebenstein DJ, Lim JE, Landry LG, Last RL (September 2002). "Arabidopsis UVR8 regulates ultraviolet-B signal transduction and tolerance and contains sequence similarity to human regulator of chromatin condensation 1". Plant Physiol. 130 (1): 234–43.  
  4. ^ Cloix C, Jenkins GI (January 2008). "Interaction of the Arabidopsis UV-B-specific signaling component UVR8 with chromatin". Mol Plant 1 (1): 118–28.  
  5. ^ Rizzini L, Favory JJ, Cloix C, Faggionato D, O'Hara A, Kaiserli E, Baumeister R, Schäfer E, Nagy F, Jenkins GI, Ulm R (April 2011). "Perception of UV-B by the Arabidopsis UVR8 protein". Science 332 (6025): 103–6.  
  6. ^ Jenkins GI (2009). "Signal transduction in responses to UV-B radiation". Annu Rev Plant Biol 60: 407–31.  
  7. ^ Cloix C, Kaiserli E, Heilmann M, Baxter KJ, Brown BA, O'Hara A, Smith BO, Christie JM, Jenkins GI (October 2012). "C-terminal region of the UV-B photoreceptor UVR8 initiates signaling through interaction with the COP1 protein". Proc. Natl. Acad. Sci. U.S.A. 109 (40): 16366–70.  
  8. ^ Heijde M, Ulm R (April 2012). "UV-B photoreceptor-mediated signalling in plants". Trends Plant Sci. 17 (4): 230–7.  

External links

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