A highly photostable monomeric red fluorescent protein

A highly photostable and bright green fluorescent protein (FP), along with its monomeric variants, has recently been reported. These FPs enable long-term live-cell imaging. However, red FPs with similarly desirable properties remain scarce. Here, we introduce mScarlet3-S2, which is up to 29 times more photostable than its precursor, mScarlet3, and surpasses all current red FPs in photostability. Using mScarlet3-S2, we imaged mitochondrial cristae dynamics with high spatiotemporal resolution over several minutes using structured illumination microscopy (SIM), with significantly less photobleaching than mScarlet3 variants. mScarlet3-S2 holds great potential for super-resolution and long-term live-cell imaging applications.