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. 2018 Feb 1;8:2195. doi: 10.1038/s41598-018-20634-4

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© The Author(s) 2018

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Allosteric binding of pppGpp to RelQ stabilizes the G-Loop. (a) Superimposition of one half of the tetramers of BsRelQ (white, PDB: 5DEC³³) and BsRelQ-pppGpp (green, PDB: 5DED³³). (b) Coordination of pppGpp in the central cleft of BsRelQ by amino acids residing in α1, β1 and α4 results in conformational changes (indicated by red arrows). (c) Interaction of Asn148 with pppGpp causes a rotation of α4 that is transmitted onto α5 through the hydrophobic core established by Phe149, Leu183 and Met187 from two subunits of BsRelQ. Concerted rotation of helices α4 and α5 enables formation of a salt bridge between Glu178 and Arg117. (d) Interactions between amino acid side chains from α5 and the G-Loop of BsRelQ are only established in presence of pppGpp and result in ordering of the G-Loop. (e) ppGpp synthesis by BsRelQ and BsRelQ variants in absence (−) and presence (+) of pppGpp. Error bars indicate the SD of three independent replicates. (f) The v/S characteristic of ppGpp synthesis by BsRelQ in presence of different amounts of pppGpp. The velocity is given in nmol per minute per nmol BsRelQ. The K_m values of BsRelQ in absence and presence of 250 µM pppGpp are indicated by dashed lines. Data of one representative experiment are shown.