NMR analysis of type III antifreeze protein intramolecular dimer - Structural basis for enhanced activity

The structure of a new antifreeze protein (AFP) variant, RD3, from antarcti c eel pout (Rhigophila dearborni) with enhanced activity has been determine d for the first time by nuclear magnetic resonance spectroscopy. RD3 compri ses a unique translational topology of two homologous type III AFP globular domains, each containing one flat, ice binding plane. The ice binding plan e of the N domain is located similar to3.5 Angstrom "behind" that of the C domain. The two ice binding planes are located laterally with an angle of 3 2 +/- 12 degrees between the planes. These results suggest that the C domai n plane of RD3 binds first to the ice {1010} prism plane in the (0001) dire ction, which induces successive ice binding of the N domain in the (0101) d irection. This manner of ice binding caused by the unique structural topolo gy of RD3 is thought to be crucial for the significant enhancement of antif reeze activity, especially at low AFP concentrations.