No abstract

Light absorption can trigger biologically relevant protein conformational changes. The light-induced structural rearrangement at the level of a photoexcited chromophore is known to occur in the femtosecond timescale and is expected to propagate through the protein as a quake-like intramolecular motion. Here we report direct experimental evidence of such ‘proteinquake’ observed in myoglobin through femtosecond X-ray solution scattering measurements performed at the Linac Coherent Light Source X-ray free-electron laser. An ultrafast increase of myoglobin radius of gyration occurs within 1 picosecond and is followed by a delayed protein expansion. As the system approaches equilibrium it undergoes damped oscillations with a ~3.6-picosecond time period. Our results unambiguously show how initially localized chemical changes can propagate at the level of the global protein conformation in the picosecond timescale.

Some organisms can survive complete dehydration and/or high temperature in a state of suspended animation called anydrobiosis, in which all metabolic processes are “switched off” however, upon rehydration, their normal life cycle is restored, without formation of irreversible damages. A common feature of these organisms, when in anhydrobiosis, is the presence of large amounts of sugar, particularly trehalose, which has been found to protect most effectively biomaterials. Several studies have attempted to understand how trehalose interacts with biomolecules. To address this problem, we performed molecular dynamics simulations of carboxy-myoglobin embedded in a trehalose aqueous solution and in a trehalose–water plasticized amorphous matrix. The results show that, in an aqueous solution, trehalose is excluded from the protein domain. This behavior extends also to the trehalose–water plasticized amorphous matrix, where we find sugar–water–protein structures with more water molecules that those derived from system concentration, and only few trehalose molecules bound to the protein, mainly through single hydrogen bonds.