Comparative analysis of sensory rhodopsin II structures in complex with a transducer and without it
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Sensory rhodopsin II (NpSRII) is a heptahelical transmembrane protein containing the retinal chromophore. In complex with another membrane protein, i.e., NpHtrII transducer, NpSRII transmits a signal into a cell, initiating negative phototaxis of Natronobacterium pharaonis. In the absence of a transducer, rhodopsin II can work as a proton pump similar to bacteriorhodopsin. The main objective of this study is to comparatively analyze receptor structures in complex with the transducer and without it to understand the mechanism of the protein switching function. Diffraction data for sensory rhodopsin II crystals grown in the lipidic cubic phase were obtained at the synchrotron x-ray source. In this paper, we present a new NpSRII structure with a resolution of 2.1 Å and the results of a comparative analysis of the obtained NpSRII structure with our previously published data on the NpSRII/NpHtrII complex structure and with two NpSRII structures without a transducer, previously published in the literature.
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