A Killer Protein

This month?s __Nature Biotechnology__ linkurl:includes an article;http://www.nature.com/nbt/journal/v24/n1/abs/nbt1175.html from Sergey Lukyanov that elevates fluorescent proteins from cool to killer. Lukyanov, of the Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences, Moscow, and colleagues report the isolation of a GFP variant called KillerRed that acts as a photosensitizer. Photosensitizers produce reactive oxygen species upon stimulation with light; KillerRed produces enough ROS to kill 96% of __E. coli__, and 40% to 60% of 293T human kidney cells, after 10 minutes. Localizing the protein to mitochondria increased cytotoxic efficiency to nearly 100% after 45 minutes. Lukyanov?s team also demonstrated the protein?s utility in CALI ? chromophore-assisted light inactivation. Irradiation of a KillerRed-beta-galactosidase fusion protein killed the enzyme?s activity in bacteria, both in vitro and in vivo. The CALI effect also worked in eukaryotic cells. Here?s the kicker: Lukyanov et al. are not the first to invent a photosensitizer, nor are they the first to figure out CALI. But whereas other strategies have required addition of some exogenous effector molecule (such as PlAsH), KillerRed is entirely genetic. Thus, the authors note, the molecule opens up a host of potential applications, including developmental studies, photodynamic therapy, and intracellular ablation of specific proteins. Interestingly, that issue of __Nature Biotech__ contains linkurl:another interesting GFP story;http://www.nature.com/nbt/journal/v24/n1/abs/nbt1172.html. GFPs often misfold when expressed as fusion proteins. But Geoffrey Waldo of Los Alamos National Laboratory and colleagues report a "superfolder" variant of the protein that doesn?t have this problem. So where the fluorescence of typical GFP constructs is dependent on folding, superfolder GFP fluorescence is actually directly related to concentration. Look for both superfolder GFP and KillerRed to make an appearance in your favorite biotech?s product catalog soon.

A Killer Protein

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