title: Two different groups of signal sequence in M-superfamily conotoxins.
abstract: M-superfamily conotoxins can be divided into four branches (M-1, M-2, M-3 and M-4) according to the number of amino acid residues in the third Cys loop. In general, it is widely accepted that the conotoxin signal peptides of each superfamily are strictly conserved. Recently, we cloned six cDNAs of novel M-superfamily conotoxins from Conus leopardus, Conus marmoreus and Conus quercinus, belonging to either M-1 or M-3 branch. These conotoxins, judging from the putative peptide sequences deducted from cDNAs, are rich in acidic residues and share highly conserved signal and pro-peptide region. However, they are quite different from the reported conotoxins of M-2 and M-4 branches even in their signal peptides, which in general are considered highly conserved for each superfamily of conotoxins. The signal sequences of M-1 and M-3 conotoxins composed of 24 residues start with MLKMGVVL-, while those of M-2 and M-4 conotoxins composed of 25 residues start with MMSKLGVL-. It is another example that different types of signal peptides can exist within a superfamily besides the I-conotoxin superfamily. In addition to the different disulfide connectivity of M-1 conotoxins from that of M-4 or M-2 conotoxins, the sequence alignment, preferential Cys codon usage and phylogenetic tree analysis suggest that M-1 and M-3 conotoxins have much closer relationship, being different from the conotoxins of other two branches (M-4 and M-2) of M-superfamily.
authors.affiliation: Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, 320 YueYang Road, Shanghai 200031, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Hui
authors.initials: H
authors.lastname: Jiang
authors.forename: Yu-Hong
authors.initials: YH
authors.lastname: Han
authors.forename: Duo-Duo
authors.initials: DD
authors.lastname: Yuan
authors.forename: Cheng-Wu
authors.initials: CW
authors.lastname: Chi
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D003001:Cloning, Molecular; D020916:Conotoxins / Q000737:chemistry* / Q000145:classification* / Q000235:genetics / Q000378:metabolism; D052078:Conus Snail / Q000235:genetics / Q000378:metabolism; D018076:DNA, Complementary / Q000737:chemistry; D005786:Gene Expression Regulation; D008969:Molecular Sequence Data; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D016415:Sequence Alignment
chemical_list: D020916:Conotoxins; D018076:DNA, Complementary