| Description |
(Z)-7-dideceb-1-yl acetate, a compound present in preovulatory urine of female Asian elephants, functions as a sex pheromone, triggering mating behaviors in male elephants. Presented work aims to ascertain the role of proteins in the female urine and in the male chemosensory organs in transport and recognition of the pheromone. High specific activity tritium labeled probes were synthesized and used to find and functionally characterize proteins that interact with the pheromone. Photoaffinity labeling with radiolabeled pheromone analog, and nondenaturing electrophoresis after incubation with the radiolabeled pheromone were used to identify proteins that bind the pheromone. Binding properties of these proteins were investigated using the violate odorant binding assay, as well as a gel filtration based binding assay. All known mammalian pheromones are secreted bound to lipocalin-type proteins. In contrast, our results show that the elephant pheromone is present in the urine bound to elephant albumin (ESA). Binding of the pheromone by ESA depends of pH - it is strong at alkaline pH of the elephant urine, and weaker in the acidic environment of the chemosensory organs. ESA is therefore likely to serve a dual role: extending the period of pheromonal activity of the excreted urine by decelerating the evaporation of the pheromone, and facilitating diction of the pheromone by releasing it in the proximity of sensory organs. Elephant ortholog of mammalian odorant binding (OBPs) was found to bind the pheromone in the trunk mucus. Pheromone binding by the OBP was found to occur slowly, which supports the hypothesis that OBP's sequester ligands. Some evidence was found in published structural data to support this hypothesis as well. This evidence is in opposition to the prevalent notion that OBP's bind and deliver ligands to sensory cells. DNAs coding for member of two large known mammalian chemoreceptor families have been cloned. These chemoreceptor families likely play a crucial role in pheromone recognition. A mode of transport and recognition of the elephant pheromone is being proposed, in which the urinary albumin delivers the pheromone to the proximity of sensory organs, the receptor proteins recognize it, and the OBP sequesters it. |
