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

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

“…(i) In the case of wt - LH–RC, the Car band originating from the optically allowed S 2 (1 1 B u + ) ← S 0 (1 1 A g – ) transition is as intense as the B880 Q y band, which is understandable in view of the BChl:Car ratio of 3:2 and the larger extinction coefficient of Car than BChl. The spectrum exhibits distinct vibronic features at 454 nm (2–0), 477 nm (1–0), and 509 nm (0–0), which can be assigned to γ-Car and its derivatives . Compared to the previously reported spectra of Rfl .…”

“…The BChls of m-LH–RC are shown in dark gray for comparison. Structural coordination of wt-LH–RC and m-LH–RC is based on PDB 8IUG and PDB 8IUN, respectively …”

“…Most recently, the cryo-EM structure of Rfl. castenholzii LH–RC with a resolution of 2.86 Å has unraveled the previously unresolved details in Car compositions and RC subunits, as well as in the polypeptides embracing the gap of the LH ring . The higher-resolution structure shows that Rfl.…”

“…castenholzii (PDB code: 8IUG). Color code: α-polypeptide, gray; β-polypeptide, light blue; B880, green; B800, marine; γ-carotene (γ-Car), orange; OH-γ-carotene glucoside ester (γ-CarGE), wheat. Zoom-in regions highlight the BChl–Car interactions.…”

“…castenholzii (m-LH–RC) and compared its excitation dynamics with those of the wild-type one (wt-LH–RC). Here, it is noteworthy that m-LH–RC binds 5 residual γ-Car molecules (Group-A) in the 2nd, 5th, 7th, 11th, and 14th subunits as revealed by its 2.85 Å structure . Femtosecond time-resolved absorption ( fs -TA) spectroscopy was carried out for the pair of LH–RCs under selective photoexcitation of B800 and B880 in the near-infrared (NIR) region, for which the spectral dynamics were examined over a broad spectral region (400–950 nm).…”