Selective Binding of Carotenoids with a Shorter Conjugated Chain to the LH2 Antenna Complex and Those with a Longer Conjugated Chain to the Reaction Center from Rubrivivax gelatinosus

Abstract

Rubrivivax gelatinosus having both the spheroidene and spirilloxanthin biosynthetic pathways produces carotenoids (Cars) with a variety of conjugated chains, which consist of different numbers of conjugated double bonds (n), including the C=C (m) and C=O (o) bonds. When grown under anaerobic conditions, the wild type produces Cars for which n = m = 9-13, whereas under semiaerobic conditions, it additionally produces Cars for which n = m + o = 10 + 1, 13 + 1, and 13 + 2. On the other hand, a mutant, in which the latter pathway is genetically blocked, produces only Cars for which n = 9 and 10 under anaerobic conditions and n = 9, 10, and 10 + 1 under semianaerobic conditions. Those Cars that were extracted from the LH2 complex (LH2) and the reaction center (RC), isolated from the wild-type and the mutant Rvi. gelatinosus, were analyzed by HPLC, and their structures were determined by mass spectrometry and 1H NMR spectroscopy. The selective binding of Cars to those pigment-protein complexes has been characterized as follows. (1) Cars with a shorter conjugated chain are selectively bound to LH2 whereas Cars with a longer conjugated chain to the RC. (2) Shorter chain Cars with a hydroxyl group are bound to LH2 almost exclusively. This rule holds either in the absence or in the presence of the keto group. The natural selection of shorter chain Cars by LH2 and longer chain Cars by the RC is discussed, on the basis of the results now available, in relation to the light-harvesting and photoprotective functions of Cars.

Composition and localization of bacteriochlorophyll a intermediates in the purple photosynthetic bacterium Rhodopseudomonas sp. Rits

“…palustris synthesizes RC-LH1 core and LH2 under high-light intensity, and the latter can be mainly substituted by LH4 which has different absorption properties from those of LH2, under low-light intensity: LH2 showed absorption bands at 800 and 850 nm in the near-infrared region, while LH4 showed only an 800-nm band (Tharia et al 1999;Hartigan et al 2002). Moreover, carotenoid composition in LH systems could be changed by variation in light intensity (Evans et al 1990;Gardiner et al 1993a), oxygen concentration (Goodwin 1956;Kakitani et al 2007), and growth phase (Schwerzmann and Bachofen 1989). Such alternations of photosynthetic apparatus have been intensively studied and are comprehended as the adaptation of purple photosynthetic bacteria to various environments, which is controlled by regulating the relevant gene expression level (Bauer et al 2003;Young and Beatty 2003;Evans et al 2005;Giraud et al 2005).…”

Purification and Partial Characterization of a Lutein-Binding Protein from Human Retina

“…In the case of the macular carotenoids, this is further emphasized by the saturation effects often observed in dietary supplementation studies (nonresponders) and the difficulty of depleting macular pigment through dietary restrictions − . In the plant and invertebrate world, numerous specific carotenoid-binding proteins have been purified and characterized from organisms as diverse as maize, bacteria, algae, lobsters, and silkworms − . By contrast, much less is known about specific carotenoid-binding proteins in vertebrates.…”

Photoprotection in intact cells of photosynthetic bacteria: quenching of bacteriochlorophyll fluorescence by carotenoid triplets

“…The tight connection between structure and photoprotective function of carotenoids has led to the idea of natural selection of configurations and conjugation lengths of Cars by the antenna and the RC (Kakitani et al 2007b;Koyama et al 2007): in LH2, shorter conjugated chain in the all-trans configuration is selected for the light harvesting function, whereas in the RC a longer conjugated chain in the 15-cis configuration is used for the photoprotective function. According to our view, the photoprotective role of Cars is not restricted to those in the RC but very effective protection takes place in the antenna, as well.…”