On the mechanism of photoinduced dimer dissociation in the plant UVR8 photoreceptor
Voityuk, Alexander A.
Marcus, Rudolph A.
Date of Issue2014
School of Physical and Mathematical Sciences
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 La 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.
DRNTU::Science::Physics::Optics and light
Proceedings of the national academy of sciences of the United States of America
© 2014 The Author(s). This paper was published in Proceedings of the National Academy of Sciences of the United States of America and is made available as an electronic reprint (preprint) with permission of the Author(s). The paper can be found at the following official DOI: http://dx.doi.org/10.1073/pnas.1402025111. One print or electronic copy may be made for personal use only. Systematic or multiple reproduction, distribution to multiple locations via electronic or other means, duplication of any material in this paper for a fee or for commercial purposes, or modification of the content of the paper is prohibited and is subject to penalties under law.