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Published April 8, 2014 | Published + Supplemental Material
Journal Article Open

On the mechanism of photoinduced dimer dissociation in the plant UVR8 photoreceptor

Abstract

UV-B absorption by the photoreceptor UV resistance locus 8 (UVR8) consisting of two identical protein units triggers a signal chain used by plants in connection with protection and repair of UV-B induced damage. X-ray structural analysis of the purified protein [Christie JM, et al. (2012) Science 335(6075):1492–1496] [Wu D, et al. (2012) Nature 484(7393): 214–220] has revealed that the dimer is held together by arginine–aspartate salt bridges. In this paper we address the initial processes in the signal chain. On the basis of high-level quantum-chemical calculations, we propose a mechanism for the photodissociation of UVR8 that consists of three steps: (i) In each monomer, multiple tryptophans form an extended light-harvesting system in which the L_a excited state of Trp233 experiences strong electrostatic stabilization by the protein environment. The strong stabilization singles out this tryptophan to be an efficient exciton acceptor that accumulates the excitation energy from the entire protein subunit. (ii) A fast decay of the locally excited state by charge separation generates the radical ion pair Trp285(+)-Trp233(−) with a dipole moment of ∼18 D. (iii) Key to the proposed mechanism is that this large dipole moment drives the breaking of the salt bridges between the two monomer subunits. The suggested mechanism for the UV-B–driven dissociation of the dimer that rests on the prominent players Trp233 and Trp285 explains the experimental results obtained from mutagenesis of UVR8.

Additional Information

© 2014 National Academy of Sciences. Contributed by Rudolph A. Marcus, February 20, 2014 (sent for review January 21, 2014). Published online before print March 17, 2014. The authors thank Lars-Oliver Essen for bringing the protein UVR8 in all its aspects to their knowledge. The authors thank William W. Parson for critically reading the manuscript and for many constructive comments. A.A.V. thanks the Ministry of Science and Innovation of Spain for financial support under Grant CTQ 2011-26573. R.A.M. thanks the Office of Naval Research and the Army Research Office for the support of his research. This work was generously supported by the Nanyang Technological University (M.-E.M.-B.). Author contributions: A.A.V. and M.-E.M.-B. designed research; A.A.V. performed research; A.A.V., R.A.M., and M.-E.M.-B. analyzed data; and A.A.V. and M.-E.M.-B. wrote the paper.

Attached Files

Published - PNAS-2014-Voityuk-5219-24.pdf

Supplemental Material - pnas.201402025SI.pdf

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