Variety of antimicrobial peptides in the Bombina maxima toad and evidence of their rapid diversification.
Antimicrobial peptides secreted by the skin of many amphibians play an important role in innate immunity. From two skin cDNA libraries of two individuals of the Chinese red belly toad (Bombina maxima), we identified 56 different antimicrobial peptide cDNA sequences, each of which encodes a precursor peptide that can give rise to two kinds of antimicrobial peptides, maximin and maximin H. Among these cDNA, we found that the mean number of nucleotide substitution per non-synonymous site in both the maximin and maximin H domains significantly exceed the mean number of nucleotide substitution per synonymous site, whereas the same pattern was not observed in other structural regions, such as the signal and propiece peptide regions, suggesting that these antimicrobial peptide genes have been experiencing rapid diversification driven by Darwinian selection. We cloned and sequenced seven genes amplified from skin or liver genomic DNA. These genes have three exons and share the same gene structure, in which both maximin and maximin H are encoded by the third exon. This suggests that alternative splicing and somatic recombination are less likely to play a role in creating the diversity of maximins and maximin Hs. The gene trees based on different domain regions revealed that domain shuffling or gene conversion among these genes might have happened frequently.
Lee
Wen-Hui
WH
Department of Animal Toxinology, Kunming Institute of Zoology, The Chinese Academy of Sciences (CAS), Kunming, P. R. China.
Li
Yan
Y
Lai
Ren
R
Li
Sha
S
Zhang
Yun
Y
Wang
Wen
W
D000595:Amino Acid Sequence; D000818:Animals; D023181:Antimicrobial Cationic Peptides / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D001001:Anura; D015139:Blotting, Southern; D019143:Evolution, Molecular; D020869:Gene Expression Profiling; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010455:Peptides / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D012867:Skin / Q000276:immunology / Q000378:metabolism*
D023181:Antimicrobial Cationic Peptides; D010446:Peptide Fragments; D010455:Peptides; C451507:maximin H1