Evolution of serum antifreeze glycoproteins Fish that live in polar waters have serum antifreeze glycoproteins (AFGPs) which allow them to tolerate temperatures of as low as –1.9°C It has been shown that fish from the north and south poles have evolved very similar AFGPs independently: AFGP of Antarctic fish, made up of a simple tripeptide repeat: evolved by recruitment of the 5' and 3' ends of an ancestral trypsinogen gene (secretory signal and 3' UTR) and de novo amplification of a 9bp Thr-Ala-Ala motif Arctic cod also have a Thr-Ala-Ala tripeptide repeat-based AFGP but this has no relationship with the trypsinogen gene Threonines are O-linked to galactosyl-N-acetylgalactosamine and periodicity of repeats matches periodicity of water molecules Convergent evolution of the tripeptide-based AFGP
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