Raman spectroscopy and imaging of protein droplet formation and aggregation

Raman microscopy offers a unique combination of chemical and spatial resolution with structural sensitivity. This makes it an ideal tool for studies of protein structural changes in heterogenous samples such as protein liquid-liquid phase separation (LLPS) and amyloid formation. These processes are characterized by the spontaneous assembly of proteins to form either microscopic liquid droplets or insoluble filaments stabilized by β-sheets. LLPS and amyloid formation are closely related, with many proteins that undergo LLPS also forming amyloids. This has led to the proposal that development of β-sheets in droplets is an initiating event in toxic amyloid formation. This review surveys recent applications of Raman microscopic methods to studies of LLPS and amyloid formation both in vitro and in cellulo.