# Dark-State-Mediated Photobleaching in mCherry-Based Red Fluorescent Proteins

## TL;DR

Researchers studied how dark states in red fluorescent proteins cause photobleaching and how to improve their brightness and stability.

## Contribution

The study introduces a framework linking photobleaching to dark-state conversion and provides insights for engineering better red fluorescent proteins.

## Key findings

- Photobleaching in RFPs is linked to dark-state conversion and ground-state recovery.
- mCherry-d shows enhanced dark-state behavior and chromophore fluctuations.
- The work offers a strategy to engineer photostable and bright red fluorescent proteins.

## Abstract

Developing bright
and photostable red fluorescent proteins (RFPs)
is one of the “holy grails” of the protein engineering
community. Despite several attempts, such fluorescent proteins (FPs)
have remained elusive. One bottleneck to engineering next-generation
RFPs is our lack of understanding of nonfluorescent or dark-state
properties in such constructs. Here, we develop a theoretical and
experimental framework that describes how photobleaching decays in
FPs relate to dark-state conversion and ground-state recovery. Our
systematic photophysical investigation of mCherry and mCherry-d, an
RFP with enhanced dark-state behavior, showed the presence of photodestructive
dark states in such FPs. Molecular dynamics simulations reveal enhanced
fluctuation around the imidazolinone end of the chromophore in mCherry-d,
potentially facilitating conversion to nonfluorescent states. Collectively,
this work quantifies dark-state kinetics and provides insights into
engineering dark states in RFPs to develop bright, yet photostable,
molecular probes.