A broad glass transition in hydrated proteins

We performed Raman and Brillouin scattering measurements to estimate glass transition temperature, Tg, of hydrated protein. The measurements reveal very broad glass transition in hydrated lysozyme with approximate Tg ∼ 180 ± 15 K. This result agrees with a broad range of Tg ∼ 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 Tg ∼ 180 K remains unknown. We emphasize the difference between the “dynamic transition”, known as a sharp rise in mean-squared atomic displacement at temperatures around TD ∼ 200-230 K, and the glass transition. They have different physical origin and should not be confused.