Schistosoma mansoni: an enkephalinergic system that may participate in internal and host-parasite signaling.
The present study is concerned with an opioid system in the human trematode Schistosoma mansoni, both as part of the endogenous chemical messenger system and as a tool in the parasite reaction to the host(s). A high-affinity opioid binding site was characterized in membrane suspensions prepared from adult worms. Scatchard analysis revealed a single class of receptors with a dissociation constant of 1.8 nM and a Bmax of 24.9 pmol/g protein for (D-Ala2, Met5)-enkephalin (DAME). The displacement experiments demonstrated that the most potent ligands were beta-endorphin, DAME, and met-enkephalin. These characteristics and the effects of various ions on DAME affinity suggest that S. mansoni has a delta-like opioid receptor, as previously described in other invertebrates. A met-enkephalin-like peptide was also characterized in a miracidial extract. Radioimmunoassay, reverse-phase HPLC, and bioassay by induction of cell conformational changes of human polymorphonuclear leukocytes revealed that the parasite peptide is very similar to authentic met-enkephalin. A met-enkephalin-like peptide was also shown to be present in adult worms and in their incubation medium. Taken together, these observations demonstrate the existence of a complete opiate system in S. mansoni. We discuss its role in molecular signaling within the parasite and in host-parasite interactions.
Duvaux-Miret
O
O
Centre d'Immunologie et de Biologie Parasitaire, INSERM U167-CNRS 624, Institut Pasteur, Lille, France.
Leung
M K
MK
Capron
A
A
Stefano
G B
GB
D000818:Animals; D001667:Binding, Competitive; D001700:Biomphalaria; D002450:Cell Communication; D006224:Cricetinae; D004744:Enkephalin, Methionine / Q000031:analogs & derivatives / Q000032:analysis / Q000378:metabolism; D004745:Enkephalins / Q000378:metabolism*; D006790:Host-Parasite Interactions; D009270:Naloxone / Q000494:pharmacology; D011863:Radioimmunoassay; D011957:Receptors, Opioid / Q000187:drug effects / Q000378:metabolism*; D012550:Schistosoma mansoni / Q000378:metabolism*; D015398:Signal Transduction; D014357:Trypsin / Q000494:pharmacology; D014361:Trypsin Inhibitors / Q000494:pharmacology; D001615:beta-Endorphin / Q000378:metabolism
D004745:Enkephalins; D011957:Receptors, Opioid; D014361:Trypsin Inhibitors; D009270:Naloxone; D004744:Enkephalin, Methionine; D001615:beta-Endorphin; C022118:enkephalinamide-Met, Ala(2)-; D014357:Trypsin