11-05 :: May/June 2011

nanotimes News in Brief

particles using L-ascorbic acid, In: Green Chemistry, Vol. 13(2011), Issue 4, Pages 900-904, DOI:10.1039/C0G- C00772B:

http://dx.doi.org/10.1039/C0GC00772B http://www.rsc.org/publishing/journals/gc/about.asp

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chia coli bacteria – the microorganism workhorses of genetic engineering, whose natural siblings are also found in the human intestine. Since the team had transferred the modified genetic blueprints for the GFP to the bacteria – including the necessary biosynthesis machinery – it incorporated the cou- marin amino acid at a very specific site into the fluorescent protein.

Protein designers at Technische Universitaet Mu- enchen (TUM) in Weihenstephan, Germany, have managed to incorporate a synthetic amino acid into the natural protein and thus to create a new kind of chimeric fluorescent bio-molecule by means of synthetic biology. By exploiting a special physical effect, the fluorescent protein glows in turquoise when excited with ultraviolet light and displays up to now unmatched properties. By extending the otherwise universal genetic code, the team of Pro- fessor Arne Skerra from the TUM Chair of Biologi- cal Chemistry was able to coerce bacterial cells to produce tailored proteins with synthetic functional groups. To put their idea to the test, they set out to crack a particularly hard nut: The scientists wanted to incorporate a non-natural amino acid at a speci- fic site into a widely used natural protein. In bio- research this protein is commonly known as “GFP” (Green Fluorescent Protein). It emits a bright green glow and stems originally from a jellyfish that uses the protein to make itself visible in the darkness of the deep sea.

The team chose a pale lavender coumarin pigment, serving as side chain of a non-natural amino acid, as the synthetic group. The scientists “fed” this artifi- cial amino acid to a laboratory culture of Escheri-

Professor Skerra: “We positioned the synthetic amino acid at a very close distance from the fluore- scence center of the natural protein.” The scientists employed the principle of the so-called Förster resonance energy transfer, or FRET. Under favorable conditions, this process of physical energy transfer allows energy to be conveyed from one stimula- ted pigment to another in a radiation-less manner. Because of the extreme proximity of the two lumi- nescent groups the pale lavender of the synthetic amino acid can no longer be detected; instead, the typical blue-green color of the fluorescent protein dominates. “What is special here, and different from the natural GFP, is that, thanks to the syntheti- cally incorporated amino acid, the fluorescence can be excited with a commercially available black-light lamp in place of an expensive dedicated LASER ap- paratus,” explains Sebastian Kuhn, who conducted these groundbreaking experiments as part of his doctoral thesis. Sebastian M. Kuhn, Marina Rubini, Michael A. Müller and Arne Skerra: Biosynthesis of a fluorescent protein with extreme pseudo-Stokes shift by introducing a geneti- cally encoded non-natural amino acid outside the fluoro- phore, In: Journal of the American Chemical Society AOP, Vol. 133(2011), February 22, 2011, Pages 3708-3711, DOI: 10.1021/ja1099787: http://pubs.acs.org/doi/abs/10.1021/ja1099787