Type I Antifreeze Proteins: Possible Origins from Chorion and Keratin Genes in Atlantic Snailfish
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Type I antifreeze proteins (AFPs) are alanine-rich α-helical polypeptides found in some species of right-eye flounders, sculpin, and snailfish. In this study, a shorthorn sculpin skin type I cDNA clone was used to probe an Atlantic snailfish liver cDNA library in order to locate expressed genes corresponding to snailfish plasma AFPs. Clones isolated from the cDNA library had sections with substantial amino acid and nucleotide sequence similarity to snailfish type I AFPs. However, further analysis revealed that the positives were actually three different liver-expressed proteins—two were eggshell proteins, while the third was a type II keratin. We propose that a shift in reading frame could produce alanine-rich candidate AFPs with possible antifreeze activity or ice crystal modification properties. Furthermore, it is plausible that one or more of the liver-expressed proteins represent the progenitors of snailfish type I AFPs.
KeywordsSnailfish Type I Antifreeze Protein Liver Keratin Chorion
We thank M. King and Dr. M. Shears at the OSC for technical assistance and the OSC divers for sample collection. We also thank Dr. Ming Kao for help with antifreeze activity measurements and Dr. Z. Gong for snailfish cDNA library construction. This work was supported by a grant from NSERC.
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