Enabling Photo-Crosslinking and Photo-Sensitizing Properties for Synthetic Fluorescent Protein Chromophores

Synthetic fluorescent protein chromophores have been reported for their singlet state fluorescence properties and applications in bioimaging, but rarely for the triplet state chemistries. Herein, we enabled their photo-sensitizing and photo-crosslinking properties through rational modulations. Extension of molecular conjugation and introduction of heavy atoms promoted the generation of reactive oxygen species. Unlike other photosensitizers, these chromophores selectively photo-crosslinked aggregated proteins and uncovered the interactome profiles. We also exemplified their general applications in chromophore-assisted light inactivation, photodynamic therapy and photo induced polymerization. Theoretical calculation, pathway analysis and transient absorption spectroscopy provided mechanistic insights for this triplet state chemistry. Overall, this work expands the function and application of synthetic fluorescent protein chromophores by enabling their triplet excited state properties.

Solvatochromic Cellular Stress Sensors Reveal the Compactness Heterogeneity and Dynamics of Aggregated Proteome

Deterioration of protein homeostasis (proteostasis) often induces aberrant proteome aggregation. Visualization and dissection of the stressed proteome are of particular interest given their association with numerous degenerative diseases. Recent progress in chemical cellular stress sensors allows for direct visualization of aggregated proteome. Beyond its localization and morphology, the physicochemical nature and the dynamics of the aggregated proteome have been challenging to explore. Herein, we developed a series of solvatochromic fluorene-based D-π-A probes that can selectively and noncovalently bind to a misfolded and aggregated proteome and report on their compactness heterogeneity upon cellular stresses. We achieved this goal by variation of the heterocyclic acceptors to modulate their solvatochromism and binding affinity to amorphous aggregated proteins. The optimized sensor P6 was capable of sensing the polarity differences among different aggregated proteins via its fluorescence emission wavelength. In live cells, P6 revealed the cellular compactness heterogeneity in the aggregated proteome upon cellular stresses. Given the combinative solvatochromic and noncovalent properties, our probe can reversibly monitor the dynamic changes in the aggregated proteome compactness upon stress and after stress recovery, suggesting its potential applications in search of therapeutics to counteract disease-causing proteome stresses.

A Solvatochromic Fluorescent Probe Reveals Polarity Heterogeneity upon Protein Aggregation in Cells

We report a crystallization-induced emission fluorophore to quantitatively interrogate the polarity of aggregated proteins. This solvatochromic probe, namely "AggRetina" probe, inherently binds to aggregated proteins and exhibits both a polarity-dependent fluorescence emission wavelength shift and a viscosity-dependent fluorescence intensity increase. Regulation of its polarity sensitivity was achieved by extending the conjugation length. Different proteins bear diverse polarity upon aggregation, leading to different resistance to proteolysis. Polarity primarily decreases during protein misfolding but viscosity mainly increases upon the formation of insoluble aggregates. We quantified the polarity of aggregated protein-of-interest in live cells via HaloTag bioorthogonal labeling, revealing polarity heterogeneity within cellular aggregates. The enriched micro-environment details inside misfolded and aggregated proteins may correlate to their bio-chemical properties and pathogenicity.

Rational Design of Crystallization-Induced-Emission Probes To Detect Amorphous Protein Aggregation in Live Cells

Unlike amyloid aggregates, amorphous protein aggregates with no defined structures have been challenging to target and detect in a complex cellular milieu. In this study, we rationally designed sensors of amorphous protein aggregation from aggregation-induced-emission probes (AIEgens). Utilizing dicyanoisophorone as a model AIEgen scaffold, we first sensitized the fluorescence of AIEgens to a nonpolar and viscous environment mimicking the interior of amorphous aggregated proteins. We identified a generally applicable moiety (dimethylaminophenylene) for selective binding and fluorescence enhancement. Regulation of the electron-withdrawing groups tuned the emission wavelength while retaining selective detection. Finally, we utilized the optimized probe to systematically image aggregated proteome upon proteostasis network regulation. Overall, we present a rational approach to develop amorphous protein aggregation sensors from AIEgens with controllable sensitivity, spectral coverage, and cellular performance.