Purification and structural characterization of a d‐amino acid‐containing conopeptide, conomarphin, from Conus marmoreus

Abstract

Cone snails, a group of gastropod animals that inhabit tropical seas, are capable of producing a mixture of peptide neurotoxins, namely conotoxins, for defense and predation. Conotoxins are mainly disulfide‐rich short peptides that act on different ion channels, neurotransmitter receptors, or transporters in the nervous system. They exhibit highly diverse compositions, structures, and biological functions. In this work, a novel Cys‐free 15‐residue conopeptide from Conus marmoreus was purified and designated as conomarphin. Conomarphin is unique because of its d‐configuration Phe at the third residue from the C‐terminus, which was identified using HPLC by comparing native conomarphin fragments and the corresponding synthetic peptides cleaved by different proteases. Surprisingly, the cDNA‐encoded precursor of conomarphin was found to share the conserved signal peptide with other M‐superfamily conotoxins, clearly indicating that conomarphin should belong to the M‐superfamily, although conomarphin shares no homology with other six‐Cys‐containing M‐superfamily conotoxins. Furthermore, NMR spectroscopy experiments established that conomarphin adopts a well‐defined structure in solution, with a tight loop in the middle of the peptide and a short 310‐helix at the C‐terminus. By contrast, no loop in l‐Phe13‐conomarphin was found, which suggests that d‐Phe13 is essential for the structure of conomarphin. In conclusion, conomarphin may represent a new conotoxin family, whose biological activity remains to be identified.

Deep Venomics Reveals the Mechanism for Expanded Peptide Diversity in Cone Snail Venom

“…Two precursors Mr036 (conomarphin) and Mr037 cluster with the gene superfamily M (m-c branch) (30). Both precursors contain the cleavage site LKKR, producing a mature linear peptide of 17 amino acids, and both were expressed at relatively high levels (161 and 92 reads for Mr036 and Mr037, respectively).…”

Experimental strategies for the analysis of d-amino acid containing peptides in crustaceans: A review

“…For example, Nuclear Magnetic Resonance (NMR) experiments have been performed to confirm the presence of a d-residue in two platypus toxins, C-type natriuretic peptide (d-Leu 2 for OvCNPb) and defensin-like peptide (d-Met 2 for DLP-2) [34], [35]. In NMR experiments on the conotoxin peptide, conomorphin, it was demonstrated the DPhe 13 is necessary to form a tight loop in the middle of the peptide, as this loop was not present in the l-counterpart of the toxin [36].…”

In the picture: disulfide-poor conopeptides, a class of pharmacologically interesting compounds

“…The peptides containing D -Val were termed conophans while the peptides with γ-hydroxyvaline were named γ-hydroxyconophans (Table 8). Conophans are not the only conopeptides including D -amino acids, other examples are contryphan-R [20], conomap-Vt [53] and conomarphin [54]. The latter two will be discussed in the following sections.…”

“…Conomarphin was discovered in 2008 by Han et al [54]. The cDNA-encoded precursor of conomarphin shares the conserved signal peptide with peptides from the M-superfamily, but the amino acid sequence of this peptide totally differs from other members of this superfamily.…”