Novel αD-Conopeptides and Their Precursors Identified by cDNA Cloning Define the D-Conotoxin Superfamily

alpha D-Conotoxins are peptide inhibitors of nicotinic acetylcholine receptors (nAChRs) first described from Conus vexillum (alpha D-VxXIIA-C and renamed here to alpha D-VxXXA, alpha D-VxXXB, and alpha D-VxXXC). In this study, we report cDNA sequences encoding D-superfamily conopeptides identified in the Clade XII Conidae Conus vexillum, Conus capitaneus, Conus mustelinus, and Conus miles, together with partial sequences of corresponding peptides from this family. The D-superfamily signal peptide sequences display greater heterogeneity than reported for other conotoxin superfamilies. Phylogenetic analysis of the relationships among alpha D-conotoxin precursors reveals two distinct groups containing either an EMM or AVV signal peptide sequence motif. Homodimer and heterodimer combinations of predicted mature toxin sequences likely account for the partial amino acid sequences and mass values observed for several of the native dimeric peptide components identified in C. capitaneus, C. miles, and C. mustelinus venom. The discovery of the precursors and several novel conotoxins from different species defines this large conotoxin family and expands our understanding of sequence diversification mechanisms in Conus species.