TPE-MI (Synonyms: Tetraphenylethene maleimide)

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 [1][2].

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[1].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[1].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[1].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].

[1]. Chen MZ, et al. A thiol probe for measuring unfolded protein load and proteostasis in cells. Nat Commun. 2017;8(1):474. Published 2017 Sep 7. [2]. Hu Q, et al. In Situ Monitored Vortex Fluidic-Mediated Protein Refolding/Unfolding Using an Aggregation-Induced Emission Bioprobe. Molecules. 2021;26(14):4273. Published 2021 Jul 14.