Characterization of novel conotoxins derived from the milked-venom of Conus magus

Abstract

This investigation focused on synthetic peptides derived from Conus magus as potential tools in drug discovery and as pharmacological agents themselves. The starting point was the previously discovered natural compound αM1. In addition the newly discovered αM1280 was also produced as well as a novel hybrid intermediate αM1des[Gly]1. The αM1des[Gly]1 was designed as an intermediate differing by a sole amino acid at the N-terminus. These three peptides were successfully synthesized and tested with the major findings being that all three peptides bind nicotinic acetylcholine receptors (nAChR) of the muscular but not neuronal or adrenal subtypes. Moreover, these peptides showed differential toxicity. They were non-lethal to worms and snails. However the LD50 in fish showed graded responses at 18.5, 8.2 and 5.7 nmoL.g-1 for αM1280, αM1 and αM1des[Gly]1, respectively. The elucidation of specificity of receptor binding for these peptides provides tools for discovering new therapeutic leads. Additionally, the differential toxicity of the engineered peptides demonstrates that peptide truncation and base substitution are valid strategies for increasing toxicity in nature and may also provide leads for pharmacological research. The secondary objective of this thesis was also successful by establishing the differential toxicity (survival time) of variant peptides from another standard C. magus backbone, M2450; in fish. Time to lethality ranged from 10 seconds to non-lethal depending on backbone substitution of cysteines and their disulfide bridge connectivity. This secondary objective provides the foundation for future classification of novel conotoxins found in the milked-venom of C. magus. The third and final objective of this thesis was to determine optimized synthesis and oxidation properties of novel peptides from the M2450 backbone. This was successful in demonstrating that oxidation conditions are critical and by introducing urea and NH4HCO3 at 4oC to the synthetic peptide, four isomers are possible with the first being most potent.