Shedding Light on Luminescence - Scientists at HZB reveal the structure of a designer protein

Band model of the fluorescent protein “Dreiklang”,<br />the structure of which was measured at the electron<br />storage ring BESSY.

Band model of the fluorescent protein “Dreiklang”,
the structure of which was measured at the electron
storage ring BESSY.

Fluorescent proteins are important investigative tools in the biosciences: Coupled to other proteins, they help us to study the processes of life inside cells and organisms at the molecular level. Fluorescent proteins are made to light up at specific target sites or to become dark again where necessary. In other words, they are switched on and off like light bulbs. Now, for the first time, at Helmholtz-Zentrum Berlin (HZB) scientists have studied the structural characteristics involved in fluorescence on one single protein crystal when switched on and when switched off. Their results are published in Nature Biotechnology (doi:10.1038/nbt.1952).

The researchers from the Max Planck Institute for Biophysical Chemistry in Göttingen and from Freie Universität Berlin performed their work on the MX Beamline BL14.2 at HZB’s electron storage ring BESSY, which is co-operated together with FU-Berlin, HU, MDC and FMP as part of the Joint Berlin MX Laboratory. The intense X-ray light on the beamline can be used to measure protein crystals at extremely high resolution. The object of study was a green-fluorescent protein dubbed “Dreiklang”. They first switched the protein crystal from fluorescent to non-fluorescent state at room temperature – they “switched it off”. Next, the scientists measured the deep-frozen crystal at around minus 170 degrees Celsius on the BESSY beamline.

“Normally a protein crystal breaks when heated back up to room temperature after measurement,” Dr. Uwe Müller, head of the HZB “Macromolecular Crystallography” workgroup, describes the special nature of the study: “In this case, however, it was possible to keep the protein functional.” The researchers brought the protein crystal back into fluorescent state at 30 degrees Celsius, then froze it and studied it a second time on the beamline. The subsequent data analysis revealed that the protein’s structure differs when switched on or switched off by the number of water molecules embedded in it.

“The study of the Dreiklang molecule broke new ground at BESSY,” Uwe Müller says. It is a designer protein that does not naturally exist in this form. Müller continues: “The MX beamline lets scientists study not only natural proteins but even entirely novel materials. The work with Dreiklang has taken us another step forward in HZB’s core research area of ‘Functional Materials’,” Müller concludes.