title: Real-time assessment of possible electromagnetic-field-induced changes in protein conformation and thermal stability.
abstract: Previous studies on possible interactions of radiofrequency electromagnetic fields (RF EMFs) with proteins have suggested that RF EMFs might affect protein structure and folding kinetics. In this study, the isolated thermosensor protein GrpE of the Hsp70 chaperone system of Escherichia coli was exposed to EMFs of various frequencies and field strengths under strictly controlled conditions. Circular dichroism spectroscopy was used to monitor possible structural changes. Simultaneously, temperature was recorded at each point of observation. The coiled-coil part of GrpE has been reported to undergo a well-defined and fully reversible folding/unfolding transition, thus facilitating the differentiation between thermal and non-thermal effects of RF EMFs. Any direct effect of EMF on the conformation and/or stability would result in a shift of the conformational equilibrium of the protein at a given temperature. Possible immediate (t ≤ 0.1 s) and delayed (t ≥ 30 s) effects of RF EMFs were investigated with sinusoidal signals of 0.1, 1.0, and 1.9 GHz at various field strengths up to 5.0 kV/m and with GSM signals at 0.3 kV/m in the protein solution. Taking the overall uncertainty of the experimental system into account, possible RF EMF-induced shifts in the conformational equilibrium of less than 1% of its total range might have been detected. The results obtained with the different experimental protocols indicate, however, that the conformational equilibrium of GrpE is insensitive to electromagnetic fields in the tested range of frequency and field strength.
authors.affiliation: Laboratory for Electromagnetics Fields and Microwave Electronics (IFH), ETH Zurich, Zurich, Switzerland.
authors.forename: Christian
authors.initials: C
authors.lastname: Beyer
authors.forename: Philipp
authors.initials: P
authors.lastname: Christen
authors.forename: Ilian
authors.initials: I
authors.lastname: Jelesarov
authors.forename: Jürg
authors.initials: J
authors.lastname: Fröhlich
mesh_terms: D002942:Circular Dichroism; D004574:Electromagnetic Fields; D004926:Escherichia coli; D029968:Escherichia coli Proteins / Q000737:chemistry*; D006360:Heat-Shock Proteins / Q000737:chemistry*; D007700:Kinetics; D010710:Phosphates / Q000737:chemistry; D017680:Potassium Compounds / Q000737:chemistry; D011487:Protein Conformation; D017510:Protein Folding; D055550:Protein Stability; D013696:Temperature
chemical_list: D029968:Escherichia coli Proteins; C489400:GrpE protein, E coli; D006360:Heat-Shock Proteins; D010710:Phosphates; D017680:Potassium Compounds; C013216:potassium phosphate
keywords: circular dichroism spectrophotometry; electromagnetic fields; protein conformation; real-time assessment; thermosensor protein GrpE