Bichromophoric dyes for wavelength shifting of dye-protein fluoromodules

Hybrid Small-Molecule/Protein Fluorescent Probes

Hybrid small-molecule/protein fluorescent probes are powerful tools for visualizing protein localization and function in living cells. These hybrid probes are constructed by diverse site-specific chemical protein labeling approaches through chemical reactions to exogenous peptide/small protein tags, enzymatic post-translational modifications, bioorthogonal reactions for genetically incorporated unnatural amino acids, and ligand-directed chemical reactions. The hybrid small-molecule/protein fluorescent probes are employed for imaging protein trafficking, conformational changes, and bioanalytes surrounding proteins. In addition, fluorescent hybrid probes facilitate visualization of protein dynamics at the single-molecule level and the defined structure with super-resolution imaging. In this review, we discuss development and the bioimaging applications of fluorescent probes based on small-molecule/protein hybrids.

A multipurpose mitochondrial NIR probe for imaging ferroptosis and mitophagy

This paper explores the use of a di-cationic fluorophore for visualizing mitochondria in live cells independent of membrane potential. Through the synthesized di-cationic fluorophore, we investigate the monitoring of viscosity, ferroptosis, stress-induced mitophagy, and lysosomal uptake of damaged mitochondria. The designed fluorophore is based on DQAsomes, cationic vesicles responsible for transporting drugs and DNA to mitochondria. The symmetric fluorophores possess two charge centres separated by an alkyl chain and are distinguished by a pyridinium group for mitochondrial selectivity, the C-12 alkyl substitution for membrane affinity, and an electron donor-π-acceptor fluorescent scaffold for intramolecular charge transfer. The synthesized fluorophores, PP and NP, emit wavelengths exceeding 600 nm, with a significant Stokes shift (130-211 nm), and NP demonstrates near-infrared emission (∼690 nm). Our study underscores the potential of these fluorophores for live-cell imaging, examining physiological responses such as viscosity and ferroptosis, and highlights their utility in investigating mitophagy damage and lysosomal uptake.

Specific and Reversible Enrichment of Early-Stage Glycated Proteome Based on Thiazolidine Chemistry and Palladium-Mediated Cleavage

Comprehensive analysis of protein glycation is important for better understanding of its formation mechanism and biological significance. The current preconcentration methods of glycated proteome mainly depend on the reversible combination of boronic acid and cis-dihydroxy group by pH adjustment, but it has inherent limitations (e.g., poor specificity and time-consuming). Herein, for the first time, a novel enrichment method for glycated peptides is proposed based on the reversible chemical reaction between aldehyde and 1,2-aminothiol groups, in which oxidized glycated peptides are captured onto the magnetic nanoparticles via thiazolidine chemistry and then released by palladium-mediated cleavage. The method is rapid, with excellent selectivity (even at a 1:1000 molar ratio of glycated peptides/nonglycated peptides) and high sensitivity (1 fmol/μL). As a good evidence, 1549 glycated peptides were identified from glycated human serum with 94.6% specificity, providing a powerful technique for high-throughput analysis of glycated peptides.

Design, synthesis and application in biological imaging of a novel red fluorescent dye based on a rhodanine derivative

A novel acceptor–donor–acceptor type molecule, namely 2-triphenylamine-1,3-dia[2-(3-ethyl-4-oxo-thiazolidin-2-ylidene)-malononitrile] (2RDNTPA), is designed and synthesized. 2RDNTPA exhibits a large Stokes shift of 244 nm and red fluorescence emission of 629 nm with a decent photoluminescence quantum yield of 13%. Furthermore, as a potential red fluorescent dye, 2RDNTPA can be applied in fluorescence imaging of living cancer cells (HepG2) with negligible cytotoxicity and a half maximal inhibitory concentration much more than 100 μM.

2RDNTPA can be applied in fluorescence imaging of living cancer cells (HepG2) with red emission of 620 nm and negligible cytotoxicity with a half maximal inhibitory concentration much more than 100 μM.

Antibody-Linked Fluorogen-Activating Proteins for Antigen Detection and Cell Ablation

We demonstrate selective labeling of cell surface proteins using fluorogen-activating proteins (FAPs) conjugated to standard immunoglobulins (IgGs). Conjugation was achieved with a polypeptide reagent comprised of an N-terminal photoactivatable Fc-binding domain and a C-terminal FAP domain. The resulting FAP-antibody conjugates were effective agents for protein detection and cell ablation in cultured mammalian cells and for visualizing cell-cell contacts using a tethered fluorogen assay. Because our approach allows FAP-antibody conjugates to be generated for most currently available IgGs, it should have broad utility for experimental and therapeutic applications.

Breaking the color barrier - a multi-selective antibody reporter offers innovative strategies of fluorescence detection

A novel bi-partite fluorescence platform exploits the high affinity and selectivity of antibody scaffolds to capture and activate small-molecule fluorogens. In this report, we investigated the property of multi-selectivity activation by a single antibody against diverse cyanine family fluorogens. Our fluorescence screen identified three cell-impermeant fluorogens, each with unique emission spectra (blue, green and red) and nanomolar affinities. Most importantly, as a protein fusion tag to G-protein-coupled receptors, the antibody biosensor retained full activity - displaying bright fluorogen signals with minimal background on live cells. Because fluorogen-activating antibodies interact with their target ligands via non-covalent interactions, we were able to perform advanced multi-color detection strategies on live cells, previously difficult or impossible with conventional reporters. We found that by fine-tuning the concentrations of the different color fluorogen molecules in solution, a user may interchange the fluorescence signal (onset versus offset), execute real-time signal exchange via fluorogen competition, measure multi-channel fluorescence via co-labeling, and assess real-time cell surface receptor traffic via pulse-chase experiments. Thus, here we inform of an innovative reporter technology based on tri-color signal that allows user-defined fluorescence tuning in live-cell applications.

Dark dyes-bright complexes: fluorogenic protein labeling

Complexes formed between organic dyes and genetically encoded proteins combine the advantages of stable and tunable fluorescent molecules and targetable, biologically integrated labels. To overcome the challenges imposed by labeling with bright fluorescent dyes, a number of approaches now exploit chemical or environmental changes to control the properties of a bound dye, converting dyes from a weakly fluorescent state to a bright, easily detectable complex. Optimized, such approaches avoid the need for removal of unbound dyes, facilitate rapid and simple assays in cultured cells and enable hybrid labeling to function more robustly in living model organisms.