How water-mediated hydrogen bonds affect chlorophyll a/b selectivity in Water-Soluble Chlorophyll Protein

Abstract

The Water-Soluble Chlorophyll Protein (WSCP) of Brassicaceae is a remarkably stable tetrapyrrole-binding protein that, by virtue of its simple design, is an exceptional model to investigate the interactions taking place between pigments and their protein scaffold and how they affect the photophysical properties and the functionality of the complexes. We investigated variants of WSCP from Lepidium virginicum (Lv) and Brassica oleracea (Bo), reconstituted with Chlorophyll (Chl) b, to determine the mechanisms by which the different Chl binding sites control their Chl a/b specificities. A combined Raman and crystallographic investigation has been employed, aimed to characterize in detail the hydrogen-bond network involving the formyl group of Chl b. The study revealed a variable degree of conformational freedom of the hydrogen bond networks among the WSCP variants, and an unexpected mixed presence of hydrogen-bonded and not hydrogen-bonded Chls b in the case of the L91P mutant of Lv WSCP. These findings helped to refine the description of the mechanisms underlying the different Chl a/b specificities of WSCP versions, highlighting the importance of the structural rigidity of the Chl binding site in the vicinity of the Chl b formyl group in granting a strong selectivity to binding sites.

Accurate Computation of the Absorption Spectrum of Chlorophyll a with Pair Natural Orbital Coupled Cluster Methods

“…Based on their study, this overlap was evident as the excitation energy of S 2 decreases as a result of the axial ligation due to HOMO – 1 destabilization. On the same principle, the heterogeneous protein environment can also modulate the Q y –Q x energy gap and other properties of the chromophores 122 through axial ligation, 78 hydrogen bonding, 123 , 124 macrocyclic ring distortion, 125 , 126 and electrostatic effects. 119 The vibrational modes of Chl a are also fine-tuned in a protein matrix for efficient energy transfer and charge separation.…”

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 water-soluble chlorophyll protein (WSCP) [1] has emerged in recent years as a promising model system for the investigation of tetrapyrroles in a protein environment [2], by virtue of its structural simplicity [3][4][5], high stability [6][7][8], and capability to be reconstituted in vitro with different tetrapyrroles [9][10][11]. Upon tetramerization of four identical protein monomers, each binding one tetrapyrrole, a homotetrameric complex in which the tetrapyrroles are organized into a "dimer of dimers" configuration is obtained (Fig.…”

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

“…An important advantage of using type II WSCPs for studying spectral tuning is the ability to rigorously modify the protein environment of the Chls by assembling them in vitro with recombinantly expressed proteins [21][22][23][24] . By implementing this strategy, Bednarczyk et al 19 demonstrated a spectral tuning mechanism based on a single-point mutation accounting for two-thirds of the spectral shifts between CaWSCP, and LvWSCP.…”