Antifreeze proteins (AFPs) have the unique ability to adsorb to ice and inhibit its growth. Many organisms ranging from fish to bacteria use AFPs to retard freezing or lessen the damage incurred upon freezing and thawing. The ice-binding mechanism of the long linear alpha-helical type I AFPs has been attributed to their regularly spaced polar residues matching the ice lattice along a pyramidal plane. In contrast, it is not known how globular antifreeze proteins such as type III AFP that lack repeating ice-binding residues bind to ice. Here we report the 1.25 A crystal structure of recombinant type III AFP (QAE isoform) from eel pout (Macrozoarces americanus), which reveals a remarkably flat amphipathic ice-binding site where five hydrogen-bonding atoms match two ranks of oxygens on the [1010] ice prism plane in the <0001> direction, giving high ice-binding affinity and specificity. This binding site, substantiated by the structures and properties of several ice-binding site mutants, suggests that the AFP occupies a niche in the ice surface in which it covers the basal plane while binding to the prism face.
PDB ID: 1MSIDownload
MMDB ID: 50356
PDB Deposition Date: 1996/10/8
Updated in MMDB: 2007/10
Experimental Method:
x-ray diffraction
Resolution: 1.25  Å
Source Organism:
Similar Structures:
Biological Unit for 1MSI: monomeric; determined by author
Molecular Components in 1MSI
Label Count Molecule
Protein (1 molecule)
Type III Antifreeze Protein Isoform Hplc 12
Molecule annotation
* Click molecule labels to explore molecular sequence information.

Citing MMDB