Single molecule flips between dim and bright states

Satoshi Habuchi et al. have characterized a reversible photoswitching system that uses individual molecules of Dronpa, a mutant of GFP cloned from the coral Pectiniidae. The authors showed that a single Dronpa molecule can flip between bright and dim states when exposed to light wavelengths of 405 and 488 nm, respectively. Dronpa can switch back and forth 100 times on a millisecond time scale. Previous reports have demonstrated photolevel switching with other GFP mutants, though many of these required minutes of illumination to trigger the switch, resulting in slow response times. Habuchi et al. suggest that the key to Dronpa’s rapid switching behavior may be that minimal structural change is required to flip from dim to bright. The authors also note that, because the chromophore in Dronpa is buried deep within its protein structure, the switching mechanism is protected from environmental influences, thus possibly making it a robust optical tag. Dronpa could be particularly useful for optically tracking the diffusion or transport of molecules in live cells. The authors say such a molecular tag could enable the development of molecular-scale devices for use in optoelectronics and bioimaging. — B.T.