From the green glow to the deep tunnel

Abstract

Biophysics Once green fluorescent protein has unleashed its eponymous green glow, a proton must journey back to the chromophore to reset the photophysical cycle. Salna et al. have now timed that journey over a temperature range from ambient temperature to down below −190 °C. Based on the large and temperature-dependent rate differences associated with isotopic substitution by deuterium, they conclude that quantum-mechanical tunneling plays a central role in the process. Specifically, the OH group on a serine residue participates in the proton transfer chain, despite its comparatively low acidity. Deep tunneling by serine's proton, at energies well below the threshold for classical deprotonation, helps bias overall transport in the right direction. Nature Chem. 10.1038/NCHEM.2527 (2016).