New Insight into the Water‐Soluble Chlorophyll‐Binding Protein from Lepidium virginicum

Abstract

This study describes new recombinant water-soluble chlorophyll (Chl)-binding proteins (WSCP) from Lepidium virginicum (LvWSCP). This complex binds four Chls (i.e. two dimers of Chls) per protein tetramer. We show that absorption, emission, hole-burned (HB) spectra and the shape of the zero-phonon hole (ZPH) action spectrum are consistent with the presence of uncorrelated excitation energy transfer between two Chl dimers. Thus, there is no need to include slow protein relaxation within the lowest excited state (as suggested in a previous analysis of cauliflower WSCP [Schmitt, F.-J. et al. (2008) J. Phys. Chem. B, 112, 13951; Pieper, J. et al. (2011) J. Phys. Chem. B, 115, 4053]) in order to explain the large shift observed between the maxima of the ZPH action and emission spectra. Experimental evidence is provided which shows that electron exchange between lowest energy Chls and the protein may occur, i.e. electrons can be trapped at low temperature by nearby aromatic amino acids. The latter explains the shape of nonresonant HB spectra (i.e. the absence of antihole), demonstrating that the hole-burning process in LvWSCP is largely photochemical in nature, though a small contribution from nonphotochemical hole burning (in resonant holes) is also observed.

Electron Nuclear Double Resonance of the Chlorophyll Triplet State in the Water-Soluble Chlorophyll Protein from Brassica oleracea: Investigation of the Effect of the Binding Site on the Hyperfine Couplings

“…The four symmetry-related chlorophyll (Chl) binding sites are identical, and therefore, the four bound chromophores experience identical protein surroundings and are spectroscopically equivalent, contrarily to chlorophyll (Chl)-binding complexes involved in photosynthesis, in which tens to hundreds of chromophores are bound in finely tuned individual binding sites [12], resulting in highly complex spectra. It follows that WSCP is an ideal model system for detailed spectroscopic investigation focused on understanding Chl-protein and Chl-Chl interactions [5,[13][14][15][16][17][18][19][20].…”

Spectral tuning of chlorophylls in proteins – electrostatics vs. ring deformation

“…Such a promising model and benchmark is the class of type II Water Soluble Chlorophyll-binding Proteins (WSCPs) from Brassicaceae. [13][14][15][16][17][18] These bind chlorophylls (Chls) with very high-affinity at 1:1 protein:pigment stoichiometry, and assemble them in homotetrameric complexes. Threedimensional structures of two complexes, namely, WSCPs from cauliflower (CaWSCP, PDB ID: 5HPZ) 19 and Virginia pepperweed (LvWSCP, PDB ID: 2DRE) 20 , are available at high-resolution, which is particularly suitable for computational modelling.…”

How Well Does the Hole-Burning Action Spectrum Represent the Site-Distribution Function of the Lowest-Energy State in Photosynthetic Pigment–Protein Complexes?

“…The parameters of the single-site spectra were previously employed to fit the Δ-FLN spectra of Cyt b 6 f 29 and/or WSCP. 24 In a system of interacting pigments, the higher-E pigment may experience NPHB (with the probability reduced according to eq 1) and/or transfer energy to the lower-E pigment; the latter may experience NPHB. The NPHB of the lowest-E pigment results in the shifts of all the excited states of the system.…”