Pigment−Pigment and Pigment−Protein Interactions in Recombinant Water-Soluble Chlorophyll Proteins (WSCP) from Cauliflower

Abstract

Plants contain water-soluble chlorophyll-binding proteins (WSCPs) that function neither as antennas nor as components of light-induced electron transfer of photosynthesis but are likely constituents of regulatory protective pathways in particular under stress conditions. This study presents results on the spectroscopic properties of recombinant WSCP from cauliflower reconstituted with chlorophyll b (Chl b) alone or with mixtures of Chl a and Chl b. Two types of experiments were performed: (a) measurements of stationary absorption spectra at 77 and 298 K and CD spectra at 298 K and (b) monitoring of laser flash-induced transient absorption changes with a resolution of 200 fs in the time domain of up to 100 ps. On the basis of a theoretical analysis outlined by Renger et al. (J. Phys. Chem. B 2007, 111, 10487) the data obtained in part (a) are interpreted within a model where tetrameric WSCP binds predominantly two Chl molecules in the form of an excitonically coupled "open sandwich" dimer with a tilt angle of about 30 degrees between the chlorin planes. The time-resolved measurements on Chl a/Chl b heterodimers are described by two exponential kinetics with time constants of 400 fs and 7 ps. These kinetics are assumed to reflect a heterogeneous population of WSCPs with Chl dimers either in excitonic coupled "open sandwich" or weakly coupled geometric arrays. The 400 fs component is assigned to excited-state relaxations from the upper to the lower excitonic level of the strongly coupled "open sandwich" dimer, while the 7-8 ps component probably indicates excitation energy transfer from 1Chl b* to Chl a in a dimer array with weak coupling due to significantly longer mutual distances between the chlorin rings.

Protein and solvent dynamics of the water-soluble chlorophyll-binding protein (WSCP)

“…A recombinant type of WSCP from cauliflower was found to contain 2 chlorophylls (class-IIa), while WSCP from Lepidium virginicum binds 4 chlorophylls per tetramer (class-IIb). Recombinant class-IIa WSCP binding only two chlorophylls has been used to investigate pigmentprotein interactions and excitation energy transfer by a number of spectroscopic techniques including timeresolved absorption and fluorescence experiments, spectral line-narrowing and 2D electronic spectroscopy [10][11][12][13][14].…”

Water-soluble chlorophyll protein (WSCP) of Arabidopsis is expressed in the gynoecium and developing silique

“…Satoh et al (1998) expressed a recombinant version of this protein fused to maltose-binding protein and showed that the protein can be reconstituted with Chl in vitro and, upon Chl binding, adopts the tetrameric form that can also be extracted from cauliflower leaves. Recombinant cauliflower WSCP, either with or without the fused maltose-binding protein, has been used extensively for studying its biochemical (Schmidt et al 2003) and spectroscopic properties such as (magnetic) circular dichroism (CD) (Hughes et al 2006), fluorescence, time-resolved absorption and fluorescence spectroscopy Theiss et al 2007;Schmitt et al 2008), fluorescence line narrowing (Pieper et al 2011a), and spectral hole burning (Pieper et al 2011b). WSCP turns out to be an excellent tool for studying Chl-Chl and Chl-protein interactions because of the low number of bound Chls and the absence of any other chromophores (Renger et al 2011).…”

Artificial photoactive proteins

“…On the other hand, they bind Chl when they are mixed with thylakoid membranes. Complexes of WSCP with Chl a and Chl d were prepared by this method to study the spectroscopic properties of Chl in a single well-defined protein environment and its exciton interactions with nearby Chl molecules (Hughes et al 2006;Theiss et al 2007). …”