Oxidative Folding Catalysts of Conotoxins Derived from the Venom Duct Transcriptome of C. frigidus and C. amadis .

Two novel redox conopeptides with proline residues outside and within the active site disulfide loop were derived from the venom duct transcriptome of the marine cone snails Conus frigidus and Conus amadis . Mature peptides with possible post-translational modification of 4-trans-hydroxylation of proline, namely, Fr874, Fr890[P1O], Fr890[P2O], Fr906, Am1038, and Am1054, have been chemically synthesized and characterized using mass spectrometry. The estimated reduction potential of cysteine disulfides of synthetic peptides varied from -298 to -328 mV, similar to the active site cysteine disulfide motifs of the redox family of proteins. Fr906/Am1054 exhibited pronounced catalytic activity and assisted in improving the yields of natively folded globular form α-conotoxin ImI. Three-dimensional (3D) structures of the redox conopeptides were optimized using computational methods and verified by 2D-ROESY NMR spectroscopy: C. frigidus peptides adopt an N-terminal helical fold and C. amadis peptides adopt distinct structures based on the Phe4-Pro/Hyp5 peptide bond configuration. The shift in the cis - trans configuration of the Phe4-Pro/Hyp5 peptide bond of Am1038/Am1054 was observed between reduced free thiol and oxidized disulfide forms of the optimized peptides. The report confirms the position-specific effect of hydroxyproline on the oxidative folding of conotoxins and sequence diversity of redox conopeptides in the venom duct of cone snails.