Dance of water molecules turns fire-coloured beetles into antifreeze artists
RUB researchers and colleagues describe new mode of action for antifreeze proteins in PNAS
Water dynamics mediates interaction between proteins and ice crystals
Protein-ice interaction: locally and over longer distances
The structure of the fire beetle antifreeze proteins resembles a triangular prism. The ice binding surface of the “prism” contains many exposed side chains, as fragments of the amino acid threonine protrude from the surface here. These side chains bind ice crystals. Up until now, it was assumed that the antifreeze proteins only interact locally with nano ice crystals and thus prevent the formation of larger ice crystals. The international group of researchers showed, however, that this interaction also takes place between proteins and ice crystals over longer distances via water molecules, which also contributes to the freeze-protection.
The dynamics of the water molecules is important for the freeze-protection
Close to the ice binding surface, the scientists observed a much slower movement of the water molecules, which differed significantly from the water movements on the non-ice-binding sides of the protein and of free water. The lower the temperature, the slower the water moved. “We suspect that the calmer water movement on the binding surface of the protein facilitates the docking of the nano ice crystals,” Martina Havenith speculated. In accordance with this, the researchers found little change in the movement of the water molecules in an inactive mutant of the antifreeze protein.
More efficient than in fish
The antifreeze proteins of the fire-coloured beetle are ten to one hundred times more active than those of Arctic and Antarctic fish that need to protect themselves against temperatures of -1.9 degrees Celsius. The insects achieve this high antifreeze activity through the combination of the two strategies: direct interaction between proteins and ice and interaction via water molecules.
Observing the role of the solvent
“The special role of water in natural antifreeze is an excellent example demonstrating that when looking at the function of a biomolecule, you not only have to consider its 3D structure, but also its entire environment - especially the solvent; in this case water,” Prof. Havenith said. This topic is the focus of the cluster of excellence RESOLV, which was launched on the 1st November 2012 at the RUB and whose spokesperson is Martina Havenith. The current studies were funded by the Volkswagen Foundation.
K. Meister, S. Ebbinghaus, Y. Xu, J.G. Duman, A.L. DeVries, M. Gruebele, D.M. Leitner, M. Havenith (2012): Long-range protein-water dynamics in hyperactive insect antifreeze proteins, PNAS, DOI: 10.1073/pnas.1214911110