Synthesis and characterization of αM-conotoxin SIIID, a reversible human α7 nicotinic acetylcholine receptor antagonist

alpha-Conotoxins, a group of small marine peptide toxins that target nAChRs with high potency and selectivity, are valuable pharmacological tools and potential drug leads. In this study, we reported the synthesis and physiological functions of a novel alpha M-superfamily conotoxin SIIID (CCGEGSSCPKYFKNNFICGCC) from a fish-hunting Conus striatus. Three SIIID isomers with different cystine connectivities were synthesized by solid-phase polypeptide synthesis and confirmed by mass spectrometry. Patch clamp experiments on HEK293 cells expressing nAChR subtypes showed that 1 mu M SIIID (1-4, 2-5, 3-6) inhibited PNU-120596 and acetylcholine induced human alpha 7 nAChR currents by 48.45%, which was higher than 5.08% of SIIID (1-5, 2-4, 3-6) and 9.57% of SIIID (1-6, 2-4, 3-5). Further study on the most active SIIID isomer showed that 10 mu M SIIID inhibited PNU-120596 and acetylcholine induced human alpha 7 nAChR currents by 76.33% but had no obvious effect on acetylcholine induced human alpha 3 beta 4 nAChR currents. In addition, SIIID inhibited PNU-120596 and acetylcholine induced human alpha 7 nAChR currents with an IC50 value of 880.71 +/- 271.91 nM, and this inhibition was reversible. Patch clamp experiments on rat DRG neurons showed that 10 mu M SIIID had <15% inhibitory effects on sodium, potassium and calcium currents. Our results suggested that SIIID would be a promising neumpharmacology tool for the study of human alpha 7 nAChR and its related diseases.

Automated summary

This study reported the synthesis and physiological functions of a novel alpha M-superfamily conotoxin SIIID, which has high potency and selectivity on nAChRs, particularly inhibiting human alpha 7 nAChR currents. It could serve as a promising tool for studying human alpha 7 nAChR and related diseases.