Conformational stability and dynamics in crystals recapitulate protein behaviour in solution

A growing body of evidences has established that in many cases proteins may preserve most of their function and flexibility in a crystalline environment, and several techniques are today capable to detect transiently-populated states of macromolecules in tightly packed lattices. Intriguingly, in the case of amyloidogenic precursors, the presence of these conformations (hidden to conventional crystallographic studies) can be correlated to the pathological fate of the native fold. It remains unclear, however, to which extent these minor conformations reflect the protein behaviour that is more commonly studied in solution. Here, we address this question by investigating some biophysical properties of a prototypical amyloidogenic system, {beta}2-microglobulin ({beta}2m) in solution and in microcrystalline state. By combining NMR chemical shifts with Molecular Dynamics (MD) simulations, we confirmed that conformational dynamics of {beta}2m native state in the crystal lattice is in keeping with what observed in solution. A comparative study of protein stability in solution and in crystallo is then carried out, monitoring the change in protein secondary structure at increasing temperature by Fourier transform infrared (FTIR) spectroscopy. The increased structural order of the crystalline state contributes to provide better resolved spectral components compared to those collected in solution and crucially, the crystalline samples display thermal stabilities in good agreement with the trend observed in solution. Overall, this work shows that protein stability and occurrence of pathological hidden states in crystals parallel their solution counterpart, confirming the interest of crystals as a platform for the biophysical characterisation of processes such as unfolding and aggregation.