Institute of Physics, Faculty of Science, University of South Bohemia, Branišovská 1760, 370 05 České Budějovice, Czech Republic.
Environmental Genomics and Systems Biology and Molecular Biophysics and Integrated Bioimaging Divisions, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
J Phys Chem B. 2020 Jun 18;124(24):4896-4905. doi: 10.1021/acs.jpcb.0c03137. Epub 2020 Jun 3.
Recently a new family of carotenoproteins, homologues of the N-terminal domain of the orange carotenoid protein (NTD-OCP), have been identified in cyanobacteria. These homologues are called helical carotenoid proteins (HCPs) as they are all predicted to maintain the all-helical structure of the NTD-OCP and to bind carotenoids. Here, HCP2 and HCP3 isolated from the cyanobacterium PCC 7601 were studied by ultrafast transient absorption spectroscopy to explore the excited-state dynamics of the bound carotenoid, canthaxanthin. The lowest excited state, S, of canthaxanthin in both HCPs yields a lifetime of 3.5 ps; it is thus shorter than for canthaxanthin in solution (4.5 ps). This is because of the longer effective conjugation of canthaxanthin in HCPs, as one of the terminal rings is in an s-trans configuration. Use of two different excitation wavelengths, 470 and 570 nm, revealed excitation wavelength dependent spectroscopic response. Additional excited-state absorption bands are observed after excitation at 470 nm for both HCPs, proving the presence of more than one ground state conformer.
最近，在蓝藻中发现了一类新的类胡萝卜素蛋白家族，它们是橙色类胡萝卜素蛋白（NTD-OCP）N 端结构域的同源物。由于它们都被预测能保持 NTD-OCP 的全螺旋结构并结合类胡萝卜素，因此这些同源物被称为螺旋类胡萝卜素蛋白（HCP）。本研究使用超快瞬态吸收光谱法对从蓝藻 PCC 7601 中分离得到的 HCP2 和 HCP3 进行了研究，以探讨结合态类胡萝卜素——角黄素的激发态动力学。在这两种 HCP 中，角黄素的最低激发态 S 的寿命为 3.5 ps；因此，它比在溶液中的角黄素（4.5 ps）短。这是因为 HCP 中角黄素的有效共轭更长，因为其中一个末端环呈 s-反式构型。使用 470nm 和 570nm 两种不同的激发波长，揭示了激发波长依赖性的光谱响应。在 470nm 激发时，两种 HCP 都观察到了额外的激发态吸收带，证明了存在不止一种基态构象。
