Genomic organization of four novel nondisulfide-bridged peptides from scorpion Mesobuthus martensii Karsch: Gaining insight into evolutionary mechanism

At least 25 nondisulfide-bridged peptides (NDBPs) have been identified and characterized from scorpions. However, the genomic organization of the genes that encode these peptides have not been reported yet. BmKa1, BmKa2 and BmKb1 are three novel genes that code for NDBPs identified by our group from Mesobuthus martensii Karsch. Based on their cDNA sequences, the genomic DNA sequences encoding these peptides were obtained using the PCR method. Sequence analysis showed that three distinct genomic structural patterns are used to encode these three peptides. The BmKa1 gene is not interrupted by any introns. However, the BmKa2 gene is composed of two exons, interrupted by a 67 bp intron that is located in the DNA region encoding the mature peptide. Two genomic homologues of the BmKb1 cDNA sequence, named BmKb1′ and BmKb2, respectively, were obtained. The BmKb1′ gene contains one intron of 593 bp, inserted into the DNA region that encodes the signal peptide. Similarly, the BmKb2 gene also contains an intron that interrupts the exon that encodes the NDBP signal peptide. The amino acid sequences deduced for BmKb2 and BmKb1′ differ only at one position. The data suggest that the genomic organizational pattern of NDBPs displays more divergence than that exhibited by the genes that encode disulfide-bridged peptides from scorpions.