Characterizing the evolution and functions of the M-superfamily conotoxins.

Conotoxins from cone snails are valuable in physiology research and therapeutic applications. Evolutionary mechanisms of conotoxins have been investigated in several superfamilies, but there is no phylogenetic analysis on M-superfamily conotoxins. In this study, we characterized identical sequences, gene structure, novel cysteine frameworks, functions and evolutionary mechanisms of M-superfamily conotoxins. Identical M-superfamily conotoxins can be found in different Conus species from the analysis of novel 467 M-superfamily conotoxin sequences and other published M-superfamily conotoxins sequences. M-superfamily conotoxin genes consist of two introns and three exons from the results of genome walking. Eighteen cysteine frameworks were identified from the M-superfamily conotoxins, and 10 of the 18 may be generated from framework III. An analysis between diet types and phylogeny of the M-superfamily conotoxins indicate that M-superfamily conotoxins might not evolve in a concerted manner but were subject to birth-and-death evolution. Codon usage analysis shows that position-specific codon conservation is not restricted to cysteines, but also to other conserved residues. By analysing primary structures and physiological functions of M-superfamily conotoxins, we proposed a hypothesis that insertions and deletions, especially insertions in the third cysteine loop, are involved in the creation of new functions and structures of the M-superfamily conotoxins.