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

Abstract

: In photosynthetic complexes, tuning of chlorophyll light-absorption spectra by the protein environment is crucial to their efficiency and robustness. Water Soluble Chlorophyll-binding Proteins from Brassicaceae (WSCPs) are useful for...

Deciphering the Spectral Tuning Mechanism in Proteorhodopsin: The Dominant Role of Electrostatics Instead of Chromophore Geometry

“…This indicates that the C 14 −C 15 bond length elongation is not the origin of the spectral tuning which is instead controlled by the direct electrostatic interactions between the protein and the retinal chromophore. A similar conclusion was reached for other photoreceptor proteins, where the geometric distortions of the chromophore are secondary to electrostatic effects [49–51] . Work by Collete et al.…”

“…A similar conclusion was reached for other photoreceptor proteins, where the geometric distortions of the chromophore are secondary to electrostatic effects. [49][50][51] Work [13,17,27] (B) Spectral shifts obtained after the removal of the protein environment.…”

Magnetophotoselection in the Investigation of Excitonically Coupled Chromophores: The Case of the Water-Soluble Chlorophyll Protein

“…Figure 1C shows an illustrative stick spectrum of the four excitonic transitions calculated in the framework of the point-dipole approximation (labelled M1, M2, M3 and M4), assuming that the Qy TDM of each monomeric Chl a is aligned with the molecular y axes, while in Figure 1D the corresponding TDMs are shown for the two most intense transitions, M3 and M2 [16]. WSCP is an ideal model system for detailed spectroscopic investigations [16,27,29,[35][36][37][38][39][40][41][42][43][44][45][46][47], particularly when compared to Chl-binding complexes involved in photosynthesis where tens to hundreds of chlorophylls are bound in finely tuned Chls binding sites along with other chromophores such as carotenoids [1,2,48]. Knowledge of the TDM orientation within the molecular structure can be obtained from magnetophotoselection (MPS) studies of triplet states performed by time-resolved electron paramagnetic resonance (TR-EPR, [49][50][51]); a summary of the key concepts of the techniques are reported in the Supporting Information.…”

Electrostatic profiling of photosynthetic pigments: implications for directed spectral tuning

“…Various factors are responsible for spectral tuning of pigments, such as long-and short-range protein electrostatics, 7,8 hydrogen bonding, 9 polarization, axial ligation, macrocyclic ring deformation, [10][11][12] and out-of-plane motion of π-conjugated functional groups of the macrocyclic ring. 13 In addition, excitonic coupling between closely placed pigments produces spectral shifts.…”

“…14 Electrostatic effects are often found to be the leading factor. [6][7][8][14][15][16][17][18][19][20][21][22][23][24][25] For example, a recent systematic study by Schapiro and coworkers 8 on Chlorophyll a based water soluble chlorophyll-binding proteins (WSCPs) demonstrated protein electrostatics to be dominant in modulating the site energy over ring deformations. In addition, the functioning of the reaction center of Photosystem II is also explicitly governed by protein electrostatics.…”