Joined: May 2002
Interesting...scrolling down to the bottom of the PNAS article, there is a link to a Science article that cited it. Guess what? Plants have evolved antifreeze proteins as well:
A Carrot Leucine-Rich-Repeat Protein That Inhibits Ice Recrystallization
Dawn Worrall, Luisa Elias, David Ashford, Maggie Smallwood, * Chris Sidebottom, Peter Lillford, Julia Telford, Chris Holt, Dianna Bowles
It appears that proteins have been coopted to antifreeze activity from other functions quite recently in evolution (20). In plants, pathogenesis-related proteins such as the (1-3)endoglucanase and chitinase of winter rye (5) and the PGIP-related carrot protein have been recruited. The cell wall is modified in response to both low temperature and pathogen attack (21). Because ice crystallizes in the apoplast, proteins involved in such cell wall modification are well suited for cooption into antifreeze activity if their protein structures permit.
PGIPs belong to a large family of proteins known as the leucine-rich-repeat (LRR) proteins (22). LRR proteins contain 10 to 30 repeated units of a ~24-amino acid peptide containing regularly spaced leucine residues. The carrot AFP consensus sequence is similar to the motif found in other LRR proteins (Fig. 3B). One LRR protein exhibits an unusual nonglobular protein structure with a solvent-exposed parallel sheet (23), and this structure has been compared with the related parallel sheet found in pectin-degrading enzymes such as pectate lyase (22). In this context, it may be relevant that fish AFPIII contains a sheet on its presumptive ice-binding face (24) and that the AFPII ice-binding face may also contain a sheet structure (25).
The co-option of an LRR protein into antifreeze function in carrot suggests an additional common structural feature of AFPs. Of the seven AFPs known (1, 2), four contain repeated sequences. Thus, a repetitive structure may correlate with antifreeze activity.
The carrot AFP can be stably produced in tobacco plants grown under normal greenhouse conditions. The RI properties of this protein may be useful for improving food storage and protecting crop plants against cold temperatures.