title: Photoswitchable Fluorescent Proteins: Do Not Always Look on the Bright Side.
abstract: Photoactivatable fluorescent proteins (FPs) have become essential markers for nanoscopy on live specimens. In this issue of ACS Nano, Wang et al. present a reversibly photoswitching FP, GMars-Q, which they promote as an advanced marker for RESOLFT imaging because of its low residual intensity in the off state and low switching fatigue. Here, we explain the observed peculiar photobleaching behavior of GMars-Q by a mechanism that involves efficient shelving of proteins in dark states, resulting in low switching fatigue and low residual off intensity. There is a continuing demand for novel FP markers with properties optimized for specific imaging techniques. Endeavors to engineer such proteins can greatly benefit from increased efforts to acquire deeper mechanistic understanding of their photophysics and photochemistry.
authors.affiliation: Institute of Applied Physics, Karlsruhe Institute of Technology , 76131 Karlsruhe, Germany.
authors.forename: Karin
authors.initials: K
authors.lastname: Nienhaus
authors.affiliation: Institute of Applied Physics, Karlsruhe Institute of Technology , 76131 Karlsruhe, Germany.|Institute of Nanotechnology, Karlsruhe Institute of Technology , 76344 Eggenstein-Leopoldshafen, Germany.|Institute of Toxicology and Genetics, Karlsruhe Institute of Technology , 76344 Eggenstein-Leopoldshafen, Germany.|Department of Physics, University of Illinois at Urbana-Champaign , Urbana, Illinois 61801, United States.
authors.forename: Gerd Ulrich
authors.initials: GU
authors.lastname: Nienhaus