Faculty of Science, University of South Bohemia, Branišovská 31, 370 05, České Budějovice, Czech Republic.
Biological Centre, Czech Academy of Sciences, Branišovská 31, 370 05, České Budějovice, Czech Republic.
Photosynth Res. 2018 Mar;135(1-3):33-43. doi: 10.1007/s11120-017-0397-4. Epub 2017 May 20.
RC-LH1-PufX complexes from a genetically modified strain of Rhodobacter sphaeroides that accumulates carotenoids with very long conjugation were studied by ultrafast transient absorption spectroscopy. The complexes predominantly bind the carotenoid diketospirilloxanthin, constituting about 75% of the total carotenoids, which has 13 conjugated C=C bonds, and the conjugation is further extended to two terminal keto groups. Excitation of diketospirilloxanthin in the RC-LH1-PufX complex demonstrates fully functional energy transfer from diketospirilloxanthin to BChl a in the LH1 antenna. As for other purple bacterial LH complexes having carotenoids with long conjugation, the main energy transfer route is via the S-Q pathway. However, in contrast to LH2 complexes binding diketospirilloxanthin, in RC-LH1-PufX we observe an additional, minor energy transfer pathway associated with the S state of diketospirilloxanthin. By comparing the spectral properties of the S state of diketospirilloxanthin in solution, in LH2, and in RC-LH1-PufX, we propose that the carotenoid-binding site in RC-LH1-PufX activates the ICT state of diketospirilloxanthin, resulting in the opening of a minor S/ICT-mediated energy transfer channel.
我们通过超快瞬态吸收光谱研究了来自积累类胡萝卜素具有非常长共轭的基因修饰的红杆菌（Rhodobacter sphaeroides）菌株的 RC-LH1-PufX 复合物。这些复合物主要结合二酮基螺旋藻黄质（diketospirilloxanthin），约占总类胡萝卜素的 75%，其具有 13 个共轭的 C=C 键，共轭进一步扩展到两个末端酮基。在 RC-LH1-PufX 复合物中二酮基螺旋藻黄质的激发表明，二酮基螺旋藻黄质与 LH1 天线中的 BChl a 之间完全实现了功能能量转移。对于其他具有长共轭的紫色细菌 LH 复合物而言，主要的能量转移途径是通过 S-Q 途径。然而，与结合二酮基螺旋藻黄质的 LH2 复合物不同，在 RC-LH1-PufX 中，我们观察到与二酮基螺旋藻黄质的 S 态相关的另一个较小的能量转移途径。通过比较溶液中二酮基螺旋藻黄质的 S 态、在 LH2 中的以及在 RC-LH1-PufX 中的光谱特性，我们提出 RC-LH1-PufX 中的类胡萝卜素结合位点激活了二酮基螺旋藻黄质的 ICT 态，从而开启了较小的 S/ICT 介导的能量转移通道。
