TPE-MI (Tetraphenylethene maleimide) is a thiol probe for measuring unfolded protein load and proteostasis in cells. TPE-MI can report imbalances in proteostasis in induced pluripotent stem cell models of Huntington disease, as well as cells transfected with mutant Huntington exon 1 before the formation of visible aggregates. TPE-MI also detects protein damage following dihydroartemisinin treatment of the malaria parasitesPlasmodium falciparum [2].In Vitro: TPE-MI is inherently non-fluorescent until it is conjugated to a thiol via the maleimide. TPE-MI fluorescence is activated upon labelling free cysteine thiols, normally buried in the core of globular proteins that are exposed upon unfolding.
TPE-MI (50?μM; 0-60 min) exhibits a homogeneous cytoplasmic labelling pattern in live HeLa cells, with a lower level of labelling in the nucleus and apparent concentration in the region of the ER, which was anticipated as a major location for protein synthesis and folding.
At the high expression level, the mutant 97Q form of Httex1 was associated with an elevated TPE-MI fluorescence signal relative to a non-disease-causing 25Q form of Httex1.
TPE-MI consists of the aggregation-induced emission (AIE) fluorogen tetraphenylethane (TPE) and the thiol-reactive group maleimide (MI), thereby possessing both AIE phenomenon and selective thiol reactivity[2].