Lateral transfer of a lectin-like antifreeze protein gene in fishes

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DOIResolve DOI: http://doi.org/10.1371/journal.pone.0002616
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TypeArticle
Journal titlePLoS ONE
ISSN1932-6203
Volume3
Issue7
Pagese2616:1e2616:11
Subjectantifreeze protein gene; fish
AbstractFishes living in icy seawater are usually protected from freezing by endogenous antifreeze proteins (AFPs) that bind to ice crystals and stop them from growing. The scattered distribution of five highly diverse AFP types across phylogenetically disparate fish species is puzzling. The appearance of radically different AFPs in closely related species has been attributed to the rapid, independent evolution of these proteins in response to natural selection caused by sea level glaciations within the last 20 million years. In at least one instance the same type of simple repetitive AFP has independently originated in two distant species by convergent evolution. But, the isolated occurrence of three very similar type II AFPs in three distantly related species (herring, smelt and sea raven) cannot be explained by this mechanism. These globular, lectin-like AFPs have a unique disulfide-bonding pattern, and share up to 85% identity in their amino acid sequences, with regions of even higher identity in their genes. A thorough search of current databases failed to find a homolog in any other species with greater than 40% amino acid sequence identity. Consistent with this result, genomic Southern blots showed the lectin-like AFP gene was absent from all other fish species tested. The remarkable conservation of both intron and exon sequences, the lack of correlation between evolutionary distance and mutation rate, and the pattern of silent vs non-silent codon changes make it unlikely that the gene for this AFP pre-existed but was lost from most branches of the teleost radiation. We propose instead that lateral gene transfer has resulted in the occurrence of the type II AFPs in herring, smelt and sea raven and allowed these species to survive in an otherwise lethal niche.
Publication date
LanguageEnglish
AffiliationNRC Institute for Marine Biosciences; National Research Council Canada
Peer reviewedYes
NRC number55502
1416
NPARC number3538315
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Record identifiera114dc1e-47ed-444c-9180-3a797af0e278
Record created2009-03-01
Record modified2016-05-09
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