Neuroactive diol and acyloin metabolites from cone snail-associated bacteria

Abstract

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.

Keywords: Natural product; Neuroassay; Symbiont.

Figure 1

Structures of compounds 1–12.

Figure 2. Activity of crude extract and compounds 2 and 8 observed by calcium imaging of dissociated DRG neurons in culture

Each trace is the response of a single neuron. Responses from ~100 neurons were monitored individually and simultaneously in a given experimental trial. Selected traces are shown from three different experimental trials. The y-axis is a measure of relative intracellular (cytoplasmic) calcium concentration, [Ca²⁺]_i, obtained by standard ratiometric calcium-imaging techniques (i.e. ratio of 340 nm/380 nm excitation while monitoring fluorescence emission at 510 nm). The x-axis is time in minutes. Increases in [Ca²⁺]_i were elicited by briefly depolarizing the neurons with 25 mM KCl, as indicated by vertical arrows. Each KCl pulse elicited an increase in [Ca²⁺]_i (by activating voltage-gated calcium channels) that is observed as a peak in each trace. After the second KCl pulse, the compound was applied to the cells for 5 minutes (horizontal bar). Both the crude extract (100 µg/mL) (A) and the two test compounds 2 (73 µM) and 8 (67 µM) (B) caused an amplification of the calcium-transient elicited by a KCl pulse.