Conformation Sensors that Distinguish Monomeric Proteins from Oligomers in Live Cells

SummaryProteins prone to misfolding form large macroscopic deposits in many neurodegenerative diseases. Yet the in situ aggregation kinetics remains poorly understood because of an inability to demarcate precursor oligomers from monomers. We developed a strategy for mapping the localization of soluble oligomers and monomers directly in live cells. Sensors for mutant huntingtin, which forms aggregates in Huntington's disease, were made by introducing a tetracysteine motif into huntingtin that becomes occluded from binding biarsenical fluorophores in oligomers, but not monomers. Up to 70% of the diffusely distributed huntingtin molecules appeared as submicroscopic oligomers in individual neuroblastoma cells expressing mutant huntingtin. We anticipate the sensors to enable insight into cellular mechanisms mediated by oligomers and monomers and for the approach to be adaptable more generally in the study of protein self-association.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (278 K)Download as PowerPoint slideHighlights► Submicroscopic oligomers of misfolded proteins, such as mutant huntingtin, are difficult to detect in live cells using established approaches ► We generated tetracysteine-tagged variants of mutant huntingtin that can only bind the biarsenical dyes FlAsH and ReAsH as monomers ► In tandem with a fluorescent protein for localization, the sensors enabled submicroscopic oligomers to be visually discerned from monomers in live cells ► The sensors showed individual cells to contain a high proportion of oligomers, distinct to the presence of large macroscopic aggregates