Shimalactone Biosynthesis Involves Spontaneous Double Bicyclo-Ring Formation with 8π-6π Electrocyclization.

Shimalactones A and B are neuritogenic polyketides possessing characteristic oxabicyclo[2.2.1]heptane and bicyclo[4.2.0]octadiene ring systems that are produced by the marine fungus Emericella variecolor GF10. We identified a candidate biosynthetic gene cluster and conducted heterologous expression analysis. Expression of ShmA polyketide synthase in Aspergillus oryzae resulted in the production of preshimalactone. Aspergillus oryzae and Saccharomyces cerevisiae transformants expressing ShmA and ShmB produced shimalactones A and B, thus suggesting that the double bicyclo-ring formation reactions proceed non-enzymatically from preshimalactone epoxide. DFT calculations strongly support the idea that oxabicyclo-ring formation and 8π-6π electrocyclization proceed spontaneously after opening of the preshimalactone epoxide ring through protonation. We confirmed the formation of preshimalactone epoxide in vitro, followed by its non-enzymatic conversion to shimalactones in the dark.

Biochemical characteristics and gene expression profiles of two paralogous luciferases from the Japanese firefly Pyrocoelia atripennis (Coleoptera, Lampyridae, Lampyrinae): insight into the evolution of firefly luciferase genes.

Two paralogous genes of firefly luciferase, Luc1 and Luc2, have been isolated from the species in two subfamilies, Luciolinae and Photurinae, of the family Lampyridae. The gene expression profiles have previously been examined only in the species of Luciolinae. Here we isolated Luc1 and Luc2 genes from the Japanese firefly Pyrocoelia atripennis. This is the first report of the presence of both Luc1 and Luc2 genes in the species of the subfamily Lampyrinae and of the exon-intron structure of Luc2 in the family Lampyridae. The luminescence of both gene products peaked at 547 nm under neutral buffer conditions, and the spectrum of Luc1, but not Luc2, was red-shifted under acidic conditions, as observed for Luc2 in the Luciolinae species. The semi-quantitative reverse transcription-polymerase chain reaction suggested that Luc1 was expressed in lanterns of all the stages except eggs, while Luc2 was expressed in the non-lantern bodies of eggs, prepupae, pupae, and female adults. These expression profiles are consistent with those in the Luciolinae species. Considering the distant phylogenetic relationship between Lampyrinae and Luciolinae in Lampyridae, we propose that fireflies generally possess two different luciferase genes and the biochemical properties and gene expression profiles for each paralog are conserved among lampyrid species.

Symbiospirols: novel long carbon-chain compounds isolated from symbiotic marine dinoflagellate Symbiodinium sp.

Symbiospirols A, B, and C, long carbon-chain compounds with a molecular weight of 1207 were isolated from the cultured symbiotic dinoflagellate Symbiodinium sp. Their planar structures and partial relative stereochemistries were elucidated based on 1D and 2D NMR spectra and a degradation reaction. Symbiospirols consisted of a C67-linear chain with a beta,beta'-dihydroxyl ketone moiety, eight hydroxyl groups, one tetrahydropyran ring, and two 1,6-dioxaspiro[4,4]nonane rings. Symbiospirol A had an inhibitory effect against l-phosphatidylserine-induced PKC activation.