Light-Quality-Adapted Carotenoid Photoprotection in the Photosystem of Roseiflexus castenholzii.

The photosystem of filamentous anoxygenic phototroph Roseiflexus (Rfl.) castenholzii comprises a light-harvesting (LH) complex encircling a reaction center (RC), which intensely absorbs blue-green light by carotenoid (Car) and near-infrared light by bacteriochlorophyll (BChl). To explore the influence of light quality (color) on the photosynthetic activity, we compared the pigment compositions and triplet excitation dynamics of the LH-RCs from Rfl. castenholzii was adapted to blue-green light (bg-LH-RC) and to near-infrared light (nir-LH-RC). Both LH-RCs bind γ-carotene derivatives; however, compared to that of nir-LH-RC (12%), bg-LH-RC contains substantially higher keto-γ-carotene content (43%) and shows considerably faster BChl-to-Car triplet excitation transfer (10.9 ns vs 15.0 ns). For bg-LH-RC, but not nir-LH-RC, selective photoexcitation of Car and the 800 nm-absorbing BChl led to Car-to-Car triplet transfer and BChl-Car singlet fission reactions, respectively. The unique excitation dynamics of bg-LH-RC enhances its photoprotection, which is crucial for the survival of aquatic anoxygenic phototrophs from photooxidative stress.

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

The light harvesting-reaction center complex (LH-RC) of Roseiflexus castenholzii binds bacteriochlorophylls a (BChls a), B800 and B880, absorbing around 800 and 880 nm, respectively. We comparatively investigated the interband excitation energy transfer (EET) dynamics of the wild-type LH-RC (wt-LH-RC) of Rfl. castenholzii and its carotenoid (Car)-less mutant (m-LH-RC) and found that Car can boost the B800 → B880 EET rate from (2.43 ps)-1 to (1.75 ps)-1, accounting for 38% acceleration of the EET process. Interestingly, photoexcitation of wt-LH-RC at 800 nm induced pronounced excitation dynamics of Car despite the insufficient photon energy for direct Car excitation, a phenomenon which is attributed to the BChl-Car exciplex 1[B800(↑↑)···Car(↓↓)]*. Such an exciplex is suggested to play an essential role in promoting the B800 → B880 EET process, as corroborated by the recently reported cryo-EM structures of wt-LH-RC and m-LH-RC. The mechanism of Car-mediated EET will be helpful to deepen the understanding of the role of Car in bacterial photosynthesis.

Inhibitory effect of astragalus membranaceus injection on apoptosis and autophagy induced by enterovirus 71 / 中国生物制品学杂志

@#Objective To investigate the effect of astragalus membranaceus（AM）injection on apoptosis and autophagy of human gastric epithelial cell line（GES⁃1）induced by enterovirus 71（EV71）. Methods GES⁃1 cells were cultured in vitro and divided into infected group（EV71 infected at a MOI of 3 and control group（no virus infected）. The morpho⁃logical changes of EV71 infected cells were observed by inverted microscope. The level of VP1 in GES⁃1 cells infected with EV71 was detected by Western blot；CCK⁃8 assay was used to detect the viability of GES⁃1 cells infected with EV71；Nuclear staining with DAPI was used to observe the morphological changes of nuclear apoptosis infected with EV71. GES⁃1 cells were divided into control group（without virus infection），infection group and AM intervention group with final concentration of 1，2. 5，5 and 10 μg／mL，respectively. Western blot was used to detect the effect of AM intervention on the expression of apoptosis⁃related proteins Caspase⁃3，PARP and autophagy⁃related proteins LC3 and P62 in GES⁃1 cells infected withEV71. CCK⁃8 method was used to detect the effect of AM intervention on the viability of GES⁃1 cells infected with EV71. Results GES⁃1 cells were round，shrunken with nuclear pyknosis and uneven size；VP1 level increased（t = 41. 56，P < 0. 01），cell viability decreased（t = 19. 07，P < 0. 01），Caspase⁃3 and PARP proteins were cut off（t = 35. 29 and 3. 648， P < 0. 01 and 0. 021 8，respectively），LC3Ⅱ／LC3Ⅰ ratio increased（t = 10. 16，P = 0. 000 5）and P62 protein was degraded（t = 68. 68，P < 0. 01）；AM inhibited the degradation of Caspase⁃3，PARP and P62 proteins induced by EV71 （t = 52. 66，59. 60 and 40. 22，respectively，each P < 0. 01）and increased the ratio of LC3Ⅱ／LC3Ⅰ（t = 5. 521，P = 0. 005 3），andreducedtheinhibitoryeffectofEV71ontheviabilityofGES⁃1cells（t =4. 420，P =0. 0115）. Conclusion EV71 infection induced apoptosis of GES⁃ 1 cells and AM intervention inhibited EV71 induced apoptosis by inhibiting EV71 induced autophagy.