Conformational and Solvation Dynamics of an Amyloidogenic Intrinsically Disordered Domain of a Melanosomal Protein

The conformational plasticity of intrinsically disordered proteins (IDPs) allows them to adopt a range of conformational states that can be important for their biological functions. The driving force for the conformational preference of an IDP emanates from an intricate interplay between chain-chain and chain-solvent interactions. Using ultrafast femtosecond and picosecond time-resolved fluorescence measurements, we characterized the conformational and solvation dynamics around the Nand C-terminal segments of a disordered repeat domain of a melanosomal protein Pmel17 that forms functional amyloid responsible for melanin biosynthesis. Our time-resolved fluorescence anisotropy results revealed slight compaction and slower rotational dynamics around the amyloidogenic C-terminal segment when compared to the proline-rich N-terminal segment of the repeat domain. The compaction of the C-terminal region was also associated with the restrained mobility of hydration water as indicated by our solvation dynamics measurements. Our findings indicate that sequence-dependent chain-solvent interactions govern both the conformational and solvation dynamics that are crucial in directing the conversion of a highly dynamic IDP into an ordered amyloid assembly. Such an interplay of amino acid composition-dependent conformational and solvation dynamics might have important physicochemical consequences in specific water-protein, ion-protein, and protein-protein interactions involved in amyloid formation and phase transitions.

Automated summary

The conformational plasticity of intrinsically disordered proteins (IDPs) is important for their biological functions, and is governed by chain-chain and chain-solvent interactions. In this study, the conformational and solvation dynamics around the N and C-terminal segments of a protein called Pmel17, which forms functional amyloid responsible for melanin biosynthesis, were characterized using fluorescence measurements. The results showed slight compaction and slower rotational dynamics around the amyloidogenic C-terminal segment compared to the proline-rich N-terminal segment. This compaction was associated with restrained mobility of hydration water. These findings highlight the importance of sequence-dependent chain-solvent interactions in directing the conversion of dynamic IDPs into ordered amyloid assemblies.