Structure and Biological Activity of a Turripeptide from Unedogemmula bisaya Venom.

The turripeptide ubi3a was isolated from the venom of the marine gastropod Unedogemmula bisaya, family Turridae, by bioassay-guided purification; both native and synthetic ubi3a elicited prolonged tremors when injected intracranially into mice. The sequence of the peptide, DCCOCOAGAVRCRFACC-NH2 (O = 4-hydroxyproline) follows the framework III pattern for cysteines (CC-C-C-CC) in the M-superfamily of conopeptides. The three-dimensional structure determined by NMR spectroscopy indicated a disulfide connectivity that is not found in conopeptides with the cysteine framework III: C1-C4, C2-C6, C3-C5. The peptide inhibited the activity of the α9α10 nicotinic acetylcholine receptor with relatively low affinity (IC50, 10.2 µM). Initial Constellation Pharmacology data revealed an excitatory activity of ubi3a on a specific subset of mouse dorsal root ganglion neurons.

Boronated tartrolon antibiotic produced by symbiotic cellulose-degrading bacteria in shipworm gills.

Shipworms are marine wood-boring bivalve mollusks (family Teredinidae) that harbor a community of closely related Gammaproteobacteria as intracellular endosymbionts in their gills. These symbionts have been proposed to assist the shipworm host in cellulose digestion and have been shown to play a role in nitrogen fixation. The genome of one strain of Teredinibacter turnerae, the first shipworm symbiont to be cultivated, was sequenced, revealing potential as a rich source of polyketides and nonribosomal peptides. Bioassay-guided fractionation led to the isolation and identification of two macrodioloide polyketides belonging to the tartrolon class. Both compounds were found to possess antibacterial properties, and the major compound was found to inhibit other shipworm symbiont strains and various pathogenic bacteria. The gene cluster responsible for the synthesis of these compounds was identified and characterized, and the ketosynthase domains were analyzed phylogenetically. Reverse-transcription PCR in addition to liquid chromatography and high-resolution mass spectrometry and tandem mass spectrometry revealed the transcription of these genes and the presence of the compounds in the shipworm, suggesting that the gene cluster is expressed in vivo and that the compounds may fulfill a specific function for the shipworm host. This study reports tartrolon polyketides from a shipworm symbiont and unveils the biosynthetic gene cluster of a member of this class of compounds, which might reveal the mechanism by which these bioactive metabolites are biosynthesized.

Neuroactive diol and acyloin metabolites from cone snail-associated bacteria.

The bacterium Gordonia sp. 647W.R.1a.05 was cultivated from the venom duct of the cone snail, Conus circumcisus. The Gordonia sp. organic extract modulated the action potential of mouse dorsal root ganglion neurons. Assay-guided fractionation led to the identification of the new compound circumcin A (1) and 11 known analogs (2-12). Two of these compounds, kurasoin B (7) and soraphinol A (8), were active in a human norepinephrine transporter assay with Ki values of 2575 and 867 nM, respectively. No neuroactivity had previously been reported for compounds in this structural class. Gordonia species have been reproducibly isolated from four different cone snail species, indicating a consistent association between these organisms.

Totopotensamides, polyketide-cyclic peptide hybrids from a mollusk-associated bacterium Streptomyces sp.

Two new compounds, the peptide-polyketide glycoside totopotensamide A (1) and its aglycone totopotensamide B (2), were isolated from a Streptomyces sp. cultivated from the gastropod mollusk Lienardia totopotens collected in the Philippines. The compounds contain a previously undescribed polyketide component, a novel 2,3-diaminobutyric acid-containing macrolactam, and a new amino acid, 4-chloro-5,7-dihydroxy-6-methylphenylglycine. The application of Marfey's method to phenylglycine derivatives was explored using quantum mechanical calculations and NMR.

Synergistic anti-methicillin-resistant Staphylococcus aureus (MRSA) activity and absolute stereochemistry of 7,8-dideoxygriseorhodin C.

The emergence of antibiotic resistance necessitates not only the identification of new compounds with antimicrobial properties, but also new strategies and combination therapies to circumvent this growing problem. Here, we report synergistic activity against methicillin-resistant Staphylococcus aureus (MRSA) of the ß-lactam antibiotic oxacillin combined with 7,8-dideoxygriseorhodin C in vitro. Ongoing efforts to identify antibiotics from marine mollusk-associated bacteria resulted in the isolation of 7,8-dideoxygriseorhodin C from a Streptomyces sp. strain cultivated from a marine gastropod tissue homogenate. Despite the long history of 7,8-dideoxygriseorhodin C in the literature, the absolute configuration has never been previously reported. A comparison of measured and calculated ECD spectra resolved the configuration of the spiroketal carbon C6, and 2D ROESY NMR spectroscopy established the absolute configuration as 6s,6aS. The compound is selective against Gram-positive bacteria including MRSA and Enterococcus faecium with an MIC range of 0.125-0.5 µg ml-1. Moreover, the compound synergizes with oxacillin against MRSA as observed in the antimicrobial microdilution and time-kill assays. Simultaneous treatment of the compound with oxacillin resulted in an approximately tenfold decrease in MIC with a combination index of <0.5, indicating synergistic anti-MRSA activity.

A bacterial source for mollusk pyrone polyketides.

In the oceans, secondary metabolites often protect otherwise poorly defended invertebrates, such as shell-less mollusks, from predation. The origins of these metabolites are largely unknown, but many of them are thought to be made by symbiotic bacteria. In contrast, mollusks with thick shells and toxic venoms are thought to lack these secondary metabolites because of reduced defensive needs. Here, we show that heavily defended cone snails also occasionally contain abundant secondary metabolites, γ-pyrones known as nocapyrones, which are synthesized by symbiotic bacteria. The bacteria, Nocardiopsis alba CR167, are related to widespread actinomycetes that we propose to be casual symbionts of invertebrates on land and in the sea. The natural roles of nocapyrones are unknown, but they are active in neurological assays, revealing that mollusks with external shells are an overlooked source of secondary metabolite diversity.