| mCherry is a monomeric red fluorescent protein engineered from a Discosoma sp. coral-derived precursor as part of the mFruit family, designed as a genetically encoded reporter that maintains red emission while reducing aggregation and cytotoxicity relative to earlier tetrameric red fluorescent proteins. The protein folds to form a β‑barrel scaffold that encloses an internal chromophore formed by autocatalytic cyclization and oxidation of its own residues, creating a rigid, shielded environment that stabilizes the excited state and supports efficient red fluorescence under physiological conditions. The chromophore environment in mCherry defines its characteristic red-shifted excitation and emission, and targeted substitutions around the chromophore pocket modulate protonation equilibria and electronic transitions to generate variants with long Stokes shift or red‑shifted spectra, illustrating how local side-chain composition tunes absorption–emission coupling without disrupting the overall monomeric fold. In living cells, mCherry functions as a constitutively fluorescent tag that reports protein localization, abundance, and dynamics when fused to target proteins, and fluorescence fluctuation spectroscopy of mCherry fusions in mammalian cells shows that the protein maintains brightness and diffusion properties compatible with single-molecule-level analyses of oligomerization and complex formation. The photophysical behavior of mCherry in the crowded intracellular environment supports quantitative measurements of brightness, molecular number, and mobility, and the spectral separation from green fluorescent protein permits dual‑color correlation and cross‑correlation approaches for dissecting coincident or independent motion of labeled partners. Variants derived from the same scaffold with altered excitation–emission profiles extend these applications by enabling multiplexed imaging and by providing templates for reporters that operate under specific illumination regimes while retaining low cytotoxicity and monomeric behavior. In bacterial systems, including strict anaerobes and plant-pathogenic species, codon-optimized mCherry constructs function as transcriptional and translational reporters under defined promoters and as C‑terminal or N‑terminal fusions that resolve periplasmic versus cytoplasmic localization, allowing precise mapping of membrane-associated and cytosolic proteins without impairing bacterial viability or virulence under the tested conditions. |
