Proteins undergo a number of changes when their temperature is dropped from the physiological range to much lower values. One of the most well-known dynamical changes undergone by proteins in a solid state is a so-called protein glass-transition, which is a dynamic transition occurring at about 200-230K leading to a loss of biological activity. Methyl groups are thought to dominate the dynamics of proteins after slow collective modes of motion freeze out in a glass-transition process.
Our previous work conducted at EMSL investigated methyl group dynamics of a key hydrophobic core leucine-69 residue in chicken villin headpiece subdomain protein (HP36) between 140-4K using deuteron NMR longitudinal relaxation measurements. A distinct increase in the apparent activation energy was observed at around 98K, indicating an abrupt freezing of methyl group dynamics. We propose to elucidate the biophysical basis of this transition by looking at site-specific data for several locations in the hydrophobic core of native and mutant HP36 samples. The main technique will be deuteron NMR longitudinal relaxation measurements with multiple echo acquisition scheme. The results will provide information on whether the phenomenon is typical for methyl groups buried in the core and whether there is a requirement of certain structural features in proximity to the methyl groups.
This work will advance our understanding of complex dynamical behavior of globular proteins. The cryogenic probes developed at PNNL make a unique opportunity for this study.
Proposal Type: Open call, standard access, non-proprietary, general
1) Vugmeyster L, Ostrovsky D, Lipton AS, J. Phys. Chem. B (2013) ?Origin of Abrupt Rise in Deuteron NMR Longitudinal Relaxation Times of Protein Methyl Groups Below 90 K? http://dx.doi.org/10.1021/jp4021596