دانلود رایگان مقاله شناسایی گونه متعدد انتشار در مجموعه آنتن کوچک جمع آوری شده

Abstract

Aggregation induced conformational change of light harvesting antenna complexes is believed to constitute one of the pathways through which photosynthetic organisms can safely dissipate the surplus of energy while exposed to saturating light. In this study, Stark fluorescence (SF) spectroscopy is applied to minor antenna complexes (CP24, CP26 and CP29) both in their light-harvesting and energy-dissipating states to trace and characterize different species generated upon energy dissipation through aggregation (in-vitro) induced conformational change. SF spectroscopy could identify three spectral species in the dissipative state of CP24, two in CP26 and only one in CP29. The comprehensive analysis of the SF spectra yielded different sets of molecular parameters for the multiple spectral species identified in CP24 or CP26, indicating the involvement of different pigments in their formation. Interestingly, a species giving emission around the 730 nm spectral region is found to form in both CP24 and CP26 following transition to the energy dissipative state, but not in CP29. The SF analyses revealed that the far red species has exceptionally large charge transfer (CT) character in the excited state. Moreover, the far red species was found to be formed invariably in both Zeaxanthin (Z)- and Violaxathin (V)-enriched CP24 and CP26 antennas with identical CT character but with larger emission yield in Z-enriched ones. This suggests that the carotenoid Z is not directly involved but only confers an allosteric effect on the formation of the far red species. Similar far red species with remarkably large CT character were also observed in the dissipative state of the major light harvesting antenna (LHCII) of plants [Wahadoszamen et al. PCCP, 2012], the fucoxanthin-chlorophyll protein (FCP) of brown algae [Wahadoszamen et al. BBA, 2014] and cyanobacterial IsiA [Wahadoszamen et al. BBA, 2015], thus pointing to identical sites and pigments active in the formation of the far red quenching species in different organisms.

5. Discussion

By applying SF spectroscopy, we could identify multiple emissive species in the quenched aggregated CP24 and CP26 minor antennas. Three species giving emission peaks at around 680, 700 and 730 nm spectral regions are found to be formed in CP24, whereas two species giving emission peaks at 690–694 and 730 nm spectral regions are generated in CP26 following aggregation. The comprehensive modeling of the SF spectra employing standard Liptay formalism yielded small but for this species. Due the involvement of a CT state in the nonradiative deactivation, clustering the Chls due to such aggregation induced modified local protein environment may potentially dissipate a large amount of excitation energy via a mechanism like concentration quenching [63,64] or open up a quenching channel to the Car [27], as aggregation is supposed to move the carotenoid (especially Lut) closer to the Chla cluster (and vice versa) within the terminal emitter domain. Similarly, by comparing the values of ZDC, Δα and Δμ with those obtained for the first quenched complexes of CP24 and CP26, we can assume that the only quenched emissive species of CP29 is generated from the enhanced Chl-Chl interaction upon aggregation. However, the SF analysis yielded nonzero magnitude of Δμ (1.03 [D]) for 5Q-Z-CP29 together with almost two times larger negative ZDC and Δα compared to 5Q-VCP29 (which gave a zero Δμ). The larger magnitudes of the ZDC and electro-optic parameters may reflect the direct the involvement of Z in energy dissipation process in CP29.