It is of fundamental and practical interest to understand how terahertz radiation affects the structure and function of proteins. We pumped protein crystals with terahertz radiation while recording x-ray diffraction images. With alternate recording by the fast readout of the Pilatus detectors we minimized the effect of temperature, X-ray radiation damage and any potential drift of the experimental station. We used the microfocus capability of the P13 beamline (EMBL, Hamburg) to probe the exposed surface of the crystal. We analyzed difference electron density maps to 1.7 Å resolution, the changes in the B-factor model after refinement and we found that 0.4 THz @ 11 mW electromagnetic radiation induces changes in a long α-helix of hen-egg white lysozyme. Further data was collected at the same beamline from orthorhombic crystals of bovine trypsin:benzamidine complex at 100 K while alternately pumping with 0.5 THz radiation with 4 mW total power. The diffraction data extend to 1.15 Å which allows the refinement of anisotropic displacement parameters, the visualization of bonding electron density and in favorable cases hydrogen atoms. At a relatively low THz photon absorption rate there are only a limited number of mechanisms that can explain protein structural changes and I will discuss those that may account for a non-thermal effect.

Non-thermal effect of terahertz radiation on crystals of lysozyme at room temperature and bovine trypsin at 100 K

253rd National Meeting (2017)

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