Asymmetry of chlorophylls in photosynthetic proteins: from the viewpoint of coordination chemistry

Abstract

We conducted a meta-analysis of (bacterio)chlorophyll [(B)Chl] molecules in photosynthetic pigment-protein complexes from the viewpoint of coordination chemistry. We surveyed the ligand species and site in the axial coordination of 146 Chl and 21 BChl molecules in 42 reported crystal structures of 12-type proteins. The imidazolyl moiety of histidine (His) is the most abundant ligand, and the second is water, a much weaker ligand. We focused on the positions, the circumstances, and the macrocycle sides for the coordination of the 31 hydrated (B)Chl molecules found in these proteins. A ligand water molecule of a hydrated (B)Chl is not necessarily hydrogen-bonded to the surrounding protein residues. A hydrated (B)Chl seems to occupy the redundant space where more strongly coupled His-Chl complexes cannot be formed. It is noted that 28 of 31 hydrated (B)Chl molecules (90) were coordinated from the α-side of the (bacterio)chlorin macrocycle, the opposite side from which the C 17-propionic ester protrudes. Among them, all five hydrated Chl molecules at the edges of the proteins were coordinated from the α-side, suggesting that (B)Chl molecules prefer this side for the coordination bondings to the β-side. The analysis also revealed that each (B)Chl binding site was composed of both the protein residues and the neighboring pigment molecules contributing roughly equally. It can be safely said that the cofactor pigments aggregated even in the proteins. Penta-coordination is advantageous to flexible adjustment of intermolecular orientations of (B)Chl molecules in the aggregates.

Coordination‐Driven Dimerization of Zinc Chlorophyll Derivatives Possessing a Dialkylamino Group

“…It has been reported that the a-ligated coordination of chlorophyllsi sp referred to the b-ligation in variousp hotosynthetic proteins. [36][37][38] Our molecular modeling study by molecular mechanics (MM +)a nd semi-empirical molecular orbitalc alculations (PM3) showedt hat the a/a-coordination dimer structure ( Figure 9) was the most energeticallys table (Figures S25-S33 and Ta ble S2).…”

Self‐Assemblies of Zinc Bacteriochlorophyll‐d Analogues Having Amide, Ester, and Urea Groups as Substituents at 17‐Position and Observation of Lamellar Supramolecular Nanostructures

“…[1][2][3] LH antennas contain severalp igments, including chlorophylls (Chls), bacteriochlorophylls (BChls), bilins, and carotenoids. [4] X-ray analysis of crystal structures of several LH antennasindicated that the pigments are located in specific arrays by binding with peptides: [5] photosystem (PS) 1, [6] PS1light harvesting complex (LHC) 1s upercomplex, [7] PS2, [8] LHC2, [9] peridinin chlorophyll protein, [10] LH1-RC, [11] LH2, [12] and Fenna-Matthews-Olson protein. [13] Chlorosomes are one of the unique LH antenna apparatuseso fg reen photosynthetic bac-teria and have attracted much attention from the viewpoints of supramolecular structures and photophysicalp roperties.…”

Reduction Processes in Biosynthesis of Chlorophyll Molecules: Chemical Implication of Enzymatically Regio- and Stereoselective Hydrogenations in the Late Stages of Their Biosynthetic Pathway

“…The concentrated excitation energy is utilized for electron transfer between chlorophyll pigments in a reaction center. These ultrafast photoinduced processes with high efficiency are performed in pigment-peptide complexes 6 or pigment self-aggregates. 7 Chlorophylls-a, -b, -c, -d, and -f are recognized as photosynthetically active pigments in oxygenic phototrophs, while bacteriochlorophylls-a, -b, -c, -d, -e, -f, and -g function in anoxygenic photosynthetic bacteria ( Figure 1).…”