Dynamic Structural Changes and Thermodynamics in Protein Phase Separation Processes of an Intrinsically Ordered-Disordered Protein Model

Elastin-like proteins (ELPs) are biologically important proteins and models for intrinsically disordered proteins (IDPs) and dynamic structural transitions associated with coacervates and liquid-liquid phase transitions. However, the conformational status below and above coacervation temperature and its role in the phase separation process is still elusive. Employing matrix least-squares global Boltzmann-fitting of the circular dichroism spectra of the ELPs (VPGVG) 20 , (VPGVG) 40 and (VPGVG) 60 , we found that coacervation occurs sharply when a certain number of repeat units has acquired β-turn conformation (in our sequence setting a threshold of ~20 repeat units). The differential scattering of the coacervate suspensions indicated that this fraction of β-turn structure is still retained after polypeptide assembly. Such conformational thresholds may also have a role in other protein assembly processes with implications for the design of protein-based smart materials.