Bioactive Polyethers

Diversified secondary metabolite biosynthesis gene repertoire revealed in symbiotic dinoflagellates

Symbiodiniaceae dinoflagellates possess smaller nuclear genomes than other dinoflagellates and produce structurally specialized, biologically active, secondary metabolites. Till date, little is known about the evolution of secondary metabolism in dinoflagellates as comparative genomic approaches have been hampered by their large genome sizes. Here, we overcome this challenge by combining genomic and metabolomics approaches to investigate how chemical diversity arises in three decoded Symbiodiniaceae genomes (clades A3, B1 and C). Our analyses identify extensive diversification of polyketide synthase and non-ribosomal peptide synthetase genes from two newly decoded genomes of Symbiodinium tridacnidorum (A3) and Cladocopium sp. (C). Phylogenetic analyses indicate that almost all the gene families are derived from lineage-specific gene duplications in all three clades, suggesting divergence for environmental adaptation. Few metabolic pathways are conserved among the three clades and we detect metabolic similarity only in the recently diverged clades, B1 and C. We establish that secondary metabolism protein architecture guides substrate specificity and that gene duplication and domain shuffling have resulted in diversification of secondary metabolism genes.

Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis (SDS-PAGE) Analysis of Palytoxin

Many natural products have been isolated from various marine organisms. These natural products, especially huge polyol and polyether compounds, are expected to be promising drug-leads. On the other hand, the accumulation of these compounds in fish and shellfish can cause food poisoning in humans. Therefore, the development of effective methods for the detection of these compounds is important from both academic and public health perspectives. We subjected palytoxin to an SDS-PAGE analysis, which is very easy, quick, and inexpensive, to determine whether this approach could be effective for detecting huge polyol natural products. Eventually, we were able to detect a band of palytoxin by SDS-PAGE analysis, which demonstrated that SDS-PAGE could be useful for detecting polyol and polyether compounds.

Zooxanthellactone, a Novel γ-Lactone-type Oxylipine from Dinoflagellates ofSymbiodiniumsp.: Structure, Distribution, and Biological Activity

A novel fatty acid derivative named zooxanthellactone (ZL) was isolated from several strains of symbiotic microalgae, dinoflagellates of the genus Symbiodinium. The metabolite is structurally related to docosahexaenoic acid (DHA) and seems to be biosynthesized by oxidation and subsequent lactonization. The absolute stereochemistry was determined from the specific rotation of the perhydro derivative. The distribution of ZL within several Symbiodinium isolates was quantitatively analyzed by HPLC techniques and suggested a relationship between the productivity of this metabolite and the Symbiodinium phylogeny. The cytotoxicity of ZL was evaluated by using human squamous cell carcinoma cell lines in comparison with that of DHA and other common fatty acids, suggesting that the long unsaturated chain was important rather than the gamma-lactone moiety.

Surface plasmon resonance biosensor method for palytoxin detection based on Na+,K+-ATPase affinity

Palytoxin (PLTX), produced by dinoflagellates from the genus Ostreopsis was first discovered, isolated, and purified from zoanthids belonging to the genus Palythoa. The detection of this toxin in contaminated shellfish is essential for human health preservation. A broad range of studies indicate that mammalian Na⁺,K⁺-ATPase is a high affinity cellular receptor for PLTX. The toxin converts the pump into an open channel that stimulates sodium influx and potassium efflux. In this work we develop a detection method for PLTX based on its binding to the Na⁺,K⁺-ATPase. The method was developed by using the phenomenon of surface plasmon resonance (SPR) to monitor biomolecular reactions. This technique does not require any labeling of components. The interaction of PLTX over immobilized Na⁺,K⁺-ATPase is quantified by injecting different concentrations of toxin in the biosensor and checking the binding rate constant (k_obs). From the representation of k_obs versus PLTX concentration, the kinetic equilibrium dissociation constant (K_D) for the PLTX-Na⁺,K⁺-ATPase association can be calculated. The value of this constant is K_D = 6.38 × 10⁻⁷ ± 6.67 × 10⁻⁸ M PLTX. In this way the PLTX-Na⁺,K⁺-ATPase association was used as a suitable method for determination of the toxin concentration in a sample. This method represents a new and useful approach to easily detect the presence of PLTX-like compounds in marine products using the mechanism of action of these toxins and in this way reduce the use of other more expensive and animal based methods.

Symbiopolyol, a VCAM-1 inhibitor from a symbiotic dinoflagellate of the jellyfish Mastigias papua

A super-carbon-chain compound, symbiopolyol (1a), was isolated from a symbiotic dinoflagellate of the jellyfish Mastigias papua. Although a direct comparison between symbiopolyol (1a) and lingshuiol B has not been completed, symbiopolyol (1a) is suggested to be the enantiomer of lingshuiol B. The structure of 1a, including its partial relative configuration, was elucidated on the basis of interpretation of spectroscopic data and chemical transformations. This compound exhibited significant inhibitory activity against the expression of VCAM-1 in human umbilical vein endothelial cells (HUVEC).

Marine huge molecules: the longest carbon chains in natural products

Marine huge polyol and polyether compounds are remarkable molecules owing to their extraordinary structures and significant biological activities. Currently, palytoxin and maitotoxin are believed to have the longest carbon chains in nature (more than 100 A in length), except for biopolymers. The structural properties of such marine huge molecules are highlighted, especially with regard to the length and shape of their carbon chains.

Recent aspects of chemical ecology: Natural toxins, coral communities, and symbiotic relationships

The discovery of new ecologically active compounds often triggers the development of basic scientific concepts in the field of biological sciences, since such compounds have direct physiological and behavioral effects on other living organisms. We have focused on the identification of natural key compounds that control biologically and physiologically intriguing phenomena. We describe three recent aspects of chemical ecology that we have investigated: natural toxins, coral communities, and symbiotic relationships. Blarina toxin (BLTX) is a lethal mammalian venom that was isolated from the short-tailed shrew. Duck-billed platypus venom shows potent Ca2+ influx in neuroblastoma cells. The venom of the solitary wasp contains arginine kinase-like protein and is used to paralyze its prey to feed its larva. The ecological behaviors of corals are controlled by combinations of small molecules. The polyol compound symbiodinolide may serve as a defense substance for symbiotic dinoflagellates to prevent digestion of their host animals. These compounds reveal the wonder of nature, in both terrestrial and marine ecological systems.

Self-Assembly of Okadaic Acid as a Pathway to the Cell

The polyether toxin okadaic acid (OA) inhibits several protein serine/threonine phosphatases that play central roles in the regulation of many essential cellular processes. The use of scanning tunneling microscopy (STM) shows that dimerization of such toxins is crucial to understand the mechanism of toxin transport across model membranes.

Bioorganic studies on marine natural products--diverse chemical structures and bioactivities

The discovery of new molecules contributes to the development of basic scientific concepts, leads to valuable drug-oriented compounds, and suggests possible new pharmacological reagents. Newly discovered substances can even be responsible for the creation of new scientific fields. Due to the radically different habitats of marine organisms, several notable examples of secondary metabolites from marine organisms have been isolated. Two of the most remarkable properties of these compounds are their structural and physiological diversities. These bioactive compounds are candidates for drugs or biological probes for physiological studies. Palytoxin is a polyol compound that shows extreme acute toxicity. Halichondrins are remarkable antitumor macrolides from sponge. Pinnatoxins, potent shellfish poisons, cause food poisoning. This paper describes bioorganic studies on such newly discovered wonders of nature. Several bioactive marine alkaloids and important substances involved in dynamic ecological systems are also described.

Shellfish poisons

In our ongoing search for bioactive metabolites from marine organisms, novel shellfish poisons have been isolated. Pinnatoxins, which are amphoteric polyether compounds, were purified from the Okinawan bivalve Pinna muricata. Pinnatoxins show acute toxicity against mice and activate Ca2+ channels. Two novel alkaloids, pinnamine and pinnaic acid, were also obtained from P. muricata. Pinnaic acid inhibits cytosolic phospholipase (cPLA2). Pteriatoxins, which are pinnatoxin analogs, were isolated from the Okinawan bivalve Pteria penguin. A nanomole-order structure determination of pteriatoxins was achieved by the detailed analysis of 2D-NMR and ESI-TOF MS/MS. This review covers the isolation, structure determination, bioactivity, synthesis, and biogenesis of these shellfish poisons and related compounds.