Thermosensor protein GrpE of heat shock protein HSP70 system as target for electromagnetic fields
ETH Zurich K 87
Zurich 8092 Switzerland
Preceptors: Ilian Jelesarov, Philipp Christen and Jürg Fröhlich
Co-authors: Christian Beyer1, Ilian Jelesarov2, Philipp Christen2 and Jürg Fröhlich1
1Information Tech and Electrical Engineering, ETH Zurich, Zurich, Switzerland. 2Biochemistry, Univ of Zurich, Zurich, Switzerland
The project is carried out as a collaborative effort of the ‘Group for Electromagnetics in Medicine and Biology’ hosted by the Laboratory for Electromagnetic Fields and Microwave Electronics at the ETH Zurich(1) and the Department of Biochemistry at the University of Zurich(2), bringing together engineers and biologists. The experimental set-up for the exposure of the protein solution to electromagnetic fields (EMF) has been constructed in the workshop at ETH and installed in the circular dichroism (CD) spectropolarimeter of the Department of Biochemistry at the University of Zurich, where also experiments and evaluations are carried out by collaborators of both institutions.
The ‘Group for Electromagnetics in Medicine and Biology’ conducts research toward applications of electromagnetic and optical principles in medical technology as well as in biomedical research. In close collaboration with academia and industry various projects are run covering magnetic resonance technology, optical spectroscopy, bioimpedance spectroscopy, wireless technologies for health care as well as risk assessment of electromagnetic fields. Regarding bioelectromagnetics, different projects including the potential effects of electromagnetic fields on biomolecular structures and cells as well as contributions to exposure assessment for epidemiological studies are conducted.
The focus of the research group of the Department of Biochemistry participating in this project is on molecular chaperones, in particular the DnaK/DnaJ/GrpE-system of Escherichia coli. GrpE, the experimental object in the project, is the nucleotide exchange factor in that system. In the past 12 years, the group has made several definitive contributions to the field, such as the introduction of fluorescence-labelled peptides for assessing the kinetics of molecular chaperone action, the discovery of the thermosensor function of GrpE, the concept of cis-action of DnaJ on DnaK in ternary (ATP·DnaK)·protein·DnaJ complexes, and the direct heat-shock response of the DnaK/DnaJ/GrpE-system.
The aim of the project presented at BioEM 2009 in Davos, Switzerland, is to design a novel real-time experiment with high reproducibility for the investigation of potential interaction of EMF on well-defined biological macromolecules, like proteins, in particular GrpE. By utilising proteins the complexity of the investigated object is reduced from the cellular to the molecular level. The new experimental set-up consists of a thermostatted exposure chamber mounted in the measurement compartment of a spectropolarimeter. With this arrangement solutions of biomacromolecules proteins can be exposed to EMF while simultaneously monitoring their conformational equilibrium in terms of secondary structure content (via measurement of the ellipticity), and the effect of the temperature on that equilibrium. Thus, the point of observation becomes identical with the potential interaction site in space and time, which will allow for the detection of even small effects of EMFs. The novel experimental unit facilitates the performance of strictly controlled real-time measurements, supports all commonly used study protocols, and allows for arbitrary pulsed exposure durations with user defined EMFs including DVBT, GSM and UMTS signals. The protein GrpE belonging to the Hsp70 chaperone system of E. coli turned out to be long-term stable for this kind of experiment. The well-defined temperature-dependence of the conformational equilibrium of GrpE may be expected to allow unequivocal differentiation between thermal and non-thermal effects of irradiation.
Future work will focus on investigating potential direct effects of RF and ELF electromagnetic field exposure on GrpE’s conformation and the kinetics of its change. If a potential effect is observed, the threshold in terms of the magnitude of the electromagnetic field can be obtained together with the frequency ranges where it occurs. Once an effect is defined and its thresholds are found, the molecular mechanisms may be explored in detail by genetic engineering of GrpE, e.g. by deleting or introducing positively or negatively charged residues.