Neutron structure of type-III antifreeze protein allows the reconstruction of XXXX -ice interface.

@entity26 @entity4968 @entity160 @entity6189 @entity30646
Antifreeze proteins (AFPs) inhibit ice growth at sub-zero temperatures. The prototypical type-III AFPs have been extensively studied, notably by X-ray crystallography, solid-state and solution NMR, and mutagenesis, leading to the identification of a compound @entity30646 ( @entity30646 ) composed of two adjacent ice-binding sections, each which binds to particular lattice planes of ice crystals, @entity4968 their growth. This surface, including many hydrophobic and some hydrophilic residues, has been extensively used to model the interaction of @entity160 with ice. Experimentally observed water molecules facing the @entity30646 have been used in an attempt to validate these models. However, these trials have been hindered by the limited capability of X-ray crystallography to reliably identify all water molecules of the hydration layer. Due to the strong diffraction signal from both the @entity26 and @entity6189 atoms, neutron diffraction provides a more effective way to determine the water molecule positions (as D(2) O). Here we report the successful structure determination at 293 K of fully perdeuterated type-III @entity160 by joint X-ray and neutron diffraction providing a very detailed description of the protein and its solvent structure. X-ray data were collected to a resolution of 1.05   , and neutron Laue data to a resolution of 1.85    with a "radically small" crystal volume of 0.13 mm(3). The identification of a tetrahedral water cluster in nuclear scattering density maps has allowed the reconstruction of the @entity30646 -bound ice crystal primary prismatic face. Analysis of the interactions between the @entity30646 and the bound ice crystal primary prismatic face indicates the role of the hydrophobic residues, which are found to bind inside the holes of the ice surface, thus explaining the specificity of AFPs for ice versus water.
