The chemistry of Briareum excavatum, a Formosan gorgonian coral, was investigated. This study has led to the isolation of five novel marine natural products, excavatolides A-E (1-5), together with brianolide (6). The structures of the above compounds were established by spectral and chemical methods. The relative configuration of excavatolide B (2) was further confirmed by a single-crystal X-ray structure analysis. Cytotoxicity of these compounds toward various cancer cell lines also is described.
Symbiosomes are specific intracellular membrane-bound vacuoles containing microalgae in a mutualistic Cnidaria (host)-dinoflagellate (symbiont) association. The symbiosome membrane is originally derived from host plasma membranes during phagocytosis of the symbiont; however, its molecular components and functions are not clear. In order to investigate the protein components of the symbiosome membranes, homogenous symbiosomes were isolated from the sea anemone Aiptasia pulchella and their purities and membrane intactness examined by Western blot analysis for host contaminants and microscopic analysis using various fluorescent probes, respectively. Pure and intact symbiosomes were then subjected to biotinylation by a cell impermeant agent (Biotin-XX sulfosuccinimidyl ester) to label membrane surface proteins. The biotinylated proteins, both Triton X-100 soluble and insoluble fractions, were subjected to 2-D SDS-PAGE and identified by MS using an LC-nano-ESI-MS/MS. A total of 17 proteins were identified. Based on their different subcellular origins and functional categories, it indicates that symbiosome membranes serve as the interface for interaction between host and symbiont by fulfilling several crucial cellular functions such as those of membrane receptors/cell recognition, cytoskeletal remodeling, ATP synthesis/proton homeostasis, transporters, stress responses/chaperones, and anti-apoptosis. The results of proteomic analysis not only indicate the molecular identity of the symbiosome membrane, but also provide insight into the possible role of symbiosome membranes during the endosymbiotic association.
Gastrodermal lipid bodies (LBs) are organelles involved in the regulation of the mutualistic endosymbiosis between reef-building corals and their dinoflagellate endosymbionts (genus Symbiodinium). As their molecular composition remains poorly defined, we herein describe the first gastrodermal LB proteome and examine in situ morphology of LBs in order to provide insight into their structure and function. After tissue separation of the tentacles of the stony coral Euphyllia glabrescens, buoyant LBs of the gastroderm encompassing a variety of sizes (0.5-4 μm in diameter) were isolated after two cycles of subcellular fractionation via stepwise sucrose gradient ultracentrifugation and detergent washing. The purity of the isolated LBs was demonstrated by their high degree of lipid enrichment and as well as the absence of contaminating proteins of the host cell and Symbiodinium. LB-associated proteins were then purified, subjected to SDS-PAGE, and identified by MS using an LC-nano-ESI-MS/MS. A total of 42 proteins were identified within eight functional groups, including metabolism, intracellular trafficking, the stress response/molecular modification and development. Ultrastructural analyses of LBs in situ showed that they exhibit defined morphological characteristics, including a high-electron density resulting from a distinct lipid composition from that of the lipid droplets of mammalian cells. Coral LBs were also characterized by the presence of numerous electron-transparent inclusions of unknown origin and composition. Both proteomic and ultrastructural observations seem to suggest that both Symbiodinium and host organelles, such as the ER, are involved in LB biogenesis.
We examined zooxanthellae diversity in scleractinian corals from southern Taiwan and the Penghu Archipelago, a tropical coral reef and a subtropical nonreefal community, respectively. Zooxanthellae diversity was investigated in 52 species of scleractinian corals from 26 genera and 13 families, using restriction fragment length polymorphism (RFLP), and phylogenetic analyses of the nuclear small-subunit ribosomal DNA (nssrDNA) and large-subunit ribosomal DNA (nlsrDNA). RFLP and phylogenetic analyses of nuclearencoded ribosomal RNA genes showed that Symbiodinium clade C was the dominant zooxanthellae in scleractinian corals in the seas around Taiwan; Symbiodinium clade D was also found in some species. Both Symbiodinium clade C and D were found in colonies of seven species of scleractinian corals. Symbiodinium clade D was associated with corals that inhabit either shallow water or the reef edge in deep water, supporting the hypothesis that Symbiodinium clade D is a relatively stress-tolerant zooxanthellae found in marginal habitats.
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