Rhodobacter capsulatus forms a compact crescent-shaped LH1–RC photocomplex

Abstract

Rhodobacter (Rba.) capsulatus has been a favored model for studies of all aspects of bacterial photosynthesis. This purple phototroph contains PufX, a polypeptide crucial for dimerization of the light-harvesting 1–reaction center (LH1–RC) complex, but lacks protein-U, a U-shaped polypeptide in the LH1–RC of its close relative Rba. sphaeroides. Here we present a cryo-EM structure of the Rba. capsulatus LH1–RC purified by DEAE chromatography. The crescent-shaped LH1–RC exhibits a compact structure containing only 10 LH1 αβ-subunits. Four αβ-subunits corresponding to those adjacent to protein-U in Rba. sphaeroides were absent. PufX in Rba. capsulatus exhibits a unique conformation in its N-terminus that self-associates with amino acids in its own transmembrane domain and interacts with nearby polypeptides, preventing it from interacting with proteins in other complexes and forming dimeric structures. These features are discussed in relation to the minimal requirements for the formation of LH1–RC monomers and dimers, the spectroscopic behavior of both the LH1 and RC, and the bioenergetics of energy transfer from LH1 to the RC.

New insights on the photocomplex of Roseiflexus castenholzii revealed from comparisons of native and carotenoid-depleted complexes

“…2 A ), respectively. Protein h occupies the exact position of the N-terminal helix of the H-subunit in all known structures of purple bacterial RC complexes ( 16 , 17 , 18 , 19 , 20 , 21 , 22 , 23 , 24 , 25 ) ( Fig. 2 B ), whereas protein I resides close to the irregular region of the LH complex ( Fig.…”

Calcium and the ecology of photosynthesis in purple sulfur bacteria

“…Curiously, however, unlike the two thermophilic species (Figures 4A and 6A), Alc. vinosum can be serially subcultured for at least seven transfers in media lacking Ca 2+ without a noticeable reduction in growth yield (Tani et al, 2024). Collectively, these results indicate that Ca 2+ plays structural and functional roles in the Alc.…”

“…vinosum Core photocomplex revealed it to be quite similar to that of Alc. tepidum in that it included multiple forms of LH1 αβ‐polypeptides (Tani et al, 2024) (Figure 9A), and six Ca 2+ were bound in a manner similar to that in the Alc. tepidum complex (Tani et al, 2022a).…”

“…tepidum (Ma et al, 2015(Ma et al, , 2016 and reviewed from work in several other purple bacteria (Kimura et al, 2023) and in the context of bioengineering for artificial photosynthesis (Noy et al, 2011). The Core photocomplex shows significant structural variation between purple bacterial species and can consist of a closed LH1 ring structure composed of 16-17 subunits, a crescent-shaped LH1 structure composed of 10-15 subunits or an S-shaped LH1 structure composed of 28-30 subunits (Gardiner et al, 2020;Swainsbury et al, 2023;Tani et al, 2020Tani et al, , 2022aTani et al, , 2022bTani et al, , 2024Tani et al, , 2023. Each LH1 subunit contains two proteins (α and β) and a single layer of Bchl molecules, and the LH1 ring either completely (circular or elliptical closed ring) or partially (C-or S-shaped open ring) surrounds the RC.…”

Carotenoid-Mediated Long-Range Energy Transfer in the Light Harvesting–Reaction Center Complex from Photosynthetic Bacterium Roseiflexus castenholzii

“…Meanwhile, Car stabilizes the structure of the light-harvesting pigment–protein assemblies and protects them from the potential oxidative damage by reacting with singlet oxygen. Car is thus known as an accessory light harvester, structural stabilizer, and photoprotector in bacterial photosynthesis. − To date, both intra- and intercomplex EET processes and primary electron transfer reactions in RC have been extensively investigated, which is benefited from the continuing advances in unraveling the structural details of various core and peripheral complexes. − …”