Chae Un Kim1, Mark W. Tate2 and
Sol M. Gruner1,2
1Cornell High Energy Synchrotron Source (CHESS) and Macromolecular Crystallography at CHESS (MacCHESS), Cornell University, Ithaca, NY
2Physics Department, Cornell University, Ithaca NY
Proteins must fluctuate to perform cellular functions, such as enzymatic catalysis, protein-protein interactions, and interactions with DNA and RNA. When proteins are cooled the conformational fluctuations dampen and eventually stop, typically at 200-240 K. This is called a protein dynamical transition. Proteins below the transition temperature show no appreciable biological function. Above the transition temperature flexibility is restored and the protein becomes increasingly biologically active. The underlying physical origin of the protein dynamical transition is controversial. Water is thought to be involved, since proteins below the transition temperature behave as if they are dehydrated. But the exact nature of the water-protein coupling is not clearly understood. We studied protein dynamics inside high-pressure cryocooled protein crystals and observed a protein dynamical transition as low as 110K. This unexpected protein dynamical transition precisely correlated with the cryogenic phase transition of water from high-density amorphous to low-density amorphous state. The results provide new insights into the underlying mechanism of protein dynamical transition and its relationship with the unusual physical properties of supercooled water.
 Chae Un Kim, Mark W. Tate and Sol M. Gruner; "Protein Dynamical Transition at 110 K", Proc. Natl. Acad. Sci. 108, 20897-20901 (2011)
 Chae Un Kim, Buz Barstow, Mark W. Tate and Sol M. Gruner; "Evidence for Liquid Water During the High-density to Low-density Amorphous Ice Transition", Proc. Natl. Acad. Sci. 106, 4596-4600 (2009)