Fluorescent Protein Fluorophore Maturation Mechanisms

Fluorescent proteins (FPs) undergo autocatalytic fluorophore formation during maturation, a process essential for their bright and stable fluorescence. After synthesis, most FPs fold, cyclize their fluorophore ring, and undergo subsequent modifications. The resulting spectral properties depend on the fluorophore structure and interactions with nearby or distant amino acid residues.

GFP and Variants

The green fluorescent protein (GFP) from Aequorea victoria forms a tripeptide chromophore (Ser65-Tyr66-Gly67). Variants like EGFP replace Ser65 with Threonine, enhancing brightness and stability.

Red Fluorescent Proteins (DsRed, eqFP611, HcRed)

DsRed, from Discosoma coral, emits at 583 nm with a stable beta-barrel structure. Far-red proteins like eqFP611 (611 nm) and HcRed (645 nm) show large Stokes shifts, useful for multi-color imaging and deep tissue visualization.

Yellow Fluorescent Protein (ZsYellow)

ZsYellow (zFP538) from Zoanthus coral emits at 538 nm, filling the spectrum between GFP and DsRed. Its unique three-ring chromophore enables yellow fluorescence in live-cell imaging.

Photoconvertible Proteins (Kaede, EosFP, Kikume)

Some FPs, like Kaede, undergo green-to-red photoconversion upon UV or violet light exposure. These optical highlighters are invaluable for tracking proteins and cells over time.