Effects of Analogs of the Fungal Sexual Pheromone Sirenin on Male Gamete Motility in Allomyces macrogynus

Abstract

ABSTRACrThe ability of various structural analogs of the sexual pheromone sirenin to attract male gametes of the aquatic fungus Allomyces macrogynus was determined. Previous studies had shown that several structural analogs and stereoisomers of natural I-sirenin were devoid of activity at physiological concentrations. We now report the discovery of a structural analog that exhibits biological activity indistinguishable from the natural pheromone. The bioassay system used to determine chemotaxis was calibrated using synthetic, racemic sirenin, which exhibited a threshold concentration for gamete attraction at an applied concentration of 10 picomolar. The new synthetic monohydroxy analog of sirenin also had a threshold concentration of 10 picomolar. In the process of developing a new total synthesis of sirenin, a variety of other analogs were prepared and tested. All of these analogs exhibited threshold concentrations at 1 micromolar or higher, although attraction at these higher concentrations still varied according to their structural resemblance to sirenin. Thus, the results of these studies demonstrate that the hydroxymethyl group attached to the six-membered ring of sirenin is not essential for biological activity at physiological concentrations. The studies with other analogs demonstrate that biological activity at any concentration involves a balance between hydrophilic hydroxyl groups and hydrophobic hydrocarbon groups in the structure.The gametes of the aquatic fungus Allomyces macrogynus exhibit a dual attraction system. It was demonstrated recently (15) that the female gametes are attracted to the male gametes as a result of the production by the male gametes of a sexual pheromone called parisin. On the other hand, it has been known for some time that the sexual pheromone sirenin (4) produced by the female gametes ofA. macrogynus has the ability to attract male gametes (7,11 or chemically synthesized l-sirenin was active; none of the analogs exhibited any biological activity in chemotaxis bioassays (8). Furthermore, Machlis (8) was able to demonstrate that d-sirenin and isosirenin lacked activity, strongly suggesting the presence of receptors with specific structural requirements. Receptor studies involving competition binding or inhibition have not been possible to carry out due to the lack of sensory adaptation to sirenin by male gametes (12, 13).More recent studies into the mechanism of male chemotaxis in A. macrogynus (13) have been hindered by the unavailability of structural analogs that can be used to determine the basic structural features of sirenin necessary for biological activity. In addition, synthetic sirenin has not been available for comparing the potency of synthetic analogs as pheromones.Results described in this report demonstrate that synthetic sirenin analogs can exhibit biological activity identical to that of naturally occurring sirenin. These results provide information about chemical recognition by the male gametes of A. macrogynus. MATERIALS AND METHODSCultures. These studies w...

The Fungal Sexual Pheromone Sirenin Activates the Human CatSper Channel Complex

“…Synthetic sirenin produced a concentration-dependent rise in [Ca 2+ ] i in human sperm with an EC 50 of 2.9 ± 0.7 μM (Figure A, black traces). As sirenin was reported to increase chemotaxis of A. macrogynus gametes at concentrations as low as 10 pM, this fungal pheromone has several orders of magnitude lower potency at the human channel, reflecting the billion years of separation between the two species. The time-course for increase in [Ca 2+ ] i elicited by sirenin was similar to that of progesterone (Figure A, red) and prostaglandin E 1 (PGE 1 , Figure A, blue), two endogenous openers of the CatSper channel.…”

External Signal-Mediated Overall Role of Hormones/Pheromones in Fungi

“…Consequently, further research has been carried out single-handedly on sirenin almost entirely by Jeffrey Pommerville. In his works, it was shown that male gametes helped in releasing a hormone that complements to sirenin, parisin which is attributed to attracting female gametes [21]. It resulted in the demonstration that there are parallels in the system of Allomyces hormone for several others that are present due to specific male as well as female hormones.…”

Gamete orientation and induction of gametogenesis by pheromones in algae and plants

“…2c), but significantly less so to isomers, including enantiomers, and other structurally related compounds (Machlis 1973). The threshold concentration for chemotaxis is of the order of lOnmol m~\ the optimum concentration is around 1 mmol m"\ The structureresponse relationship was recently investigated by Pommerville et al (1988). Sirenin is taken up and inactivated by male gametes in an unknown way (Machlis 1973).…”