ИСТИНА

The transmembrane protein signaling complex NpSRII/NpHtrII plays a key role in negative phototaxis of the halophilic archaeon Natronomonas pharaonis [1, 2]. Photon absorption induces transient structural changes in the photoreceptor sensory rhodopsin II (NpSRII) [3], which are conducted to the transducer NpHtrII. The subsequent signal propagates along the cytoplasmic part of NpHtrII to the intracellular signaling pathway [4] that modulates the rotation of the flagellum. We studied conformation and dynamics of NpSRII/NpHtrII after reconstitution in cell-membrane mimicking nanoparticles, namely, styrene maleic acid lipoprotein particles (SMALPs) [5] and lipid nanodiscs [6]. The size and shape of assembled lipid nanoparticles were characterized by atomic force microscopy (AFM). We used continuous wave (cw) electron paramagnetic resonance (EPR) spectroscopy to analyze the protein dynamics through tracking the residual motion of spin labeled side chains. We determined the interspin distance distributions between labels by pulse EPR experiments and compared the results with in silico spin-labeling rotamer analyses based on available X-ray crystallographic data. Our data indicate that NpSRII/NpHtrII complexes reconstituted in both types of nanoparticles retained their structural integrity and functionality. References 1. Klare, J. P., Bordignon, E., Engelhard, M. & Steinhoff, H. J. Eur J Cell Biol 90, (2011). 2. Klare, J. P. et al. Febs Lett 564, 219-224, (2004). 3. Wegener, A. A., Klare, J. P., Engelhard, M. & Steinhoff, H. J. Embo J 20, 5312-5319, (2001). 4. Orekhov, P. S. et al. Plos Comput Biol 11, (2015). 5. Voskoboynikova, N. et al. Rsc Adv 7, 51324-51334, (2017). 6. Orban-Glass, I. et al. Biochemistry 54, 349-362, (2015).