A broad glass transition in hydrated proteins

We performed Raman and Brillouin scattering measurements to estimate glass transition temperature, T-g, of hydrated protein. The measurements reveal very broad glass transition in hydrated lysozyme with approximate T-g similar to 180 +/- 15 K. This result agrees with a broad range of T-g similar to 160-200 K reported in literature for hydrated globular proteins and stresses the difference between behavior of hydrated biomolecules and simple glass-forming systems. Moreover, the main structural relaxation of the hydrated protein system that freezes at T-g similar to 180 K remains unknown. We emphasize the difference between the "dynamic transition", known as a sharp rise in mean-squared atomic displacement <r(2)> at temperatures around T-D similar to 200-230 K, and the glass transition. They have different physical origin and should not be confused. (C) 2009 Elsevier B.V. All rights reserved.