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. 2018 Jan 15;9:196. doi: 10.1038/s41467-017-02741-4

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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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Fig. 6 — A putative substrate-entrance tunnel. a A putative substrate-entrance tunnel in the MacAB structure (PDB: 5NIK) calculated by the program CAVER 3.0.1. The tunnel is shown in mesh and the route is indicated as dotted red lines. The gating ring and the guard helix are colored in red. The B-factor putty presentation of (b) MacB and (c) Spr0695. The electrostatics potential of TM helices is shown in transparent surface. The guard helix of Spr0695 docks to the acidic pocket of TM helices and has a relatively lower B-factor, whereas the guard helix of MacB shifts away from the pocket and the B-factor is much higher. d V_max values of the ATPase activities of Spr0694–0695, Spr0693–0694–0695 and mutants. Spr0695_M3 represents a mutant that harboring three positively charged residues Lys207, Arg208, and Lys210 on the guard helix substituted to alanine. At least three independent assays were performed to calculate the means and standard deviations, and the data are presented as the means ± S.D. Two-tailed Student’s t test is used for the comparison of statistical significance. The p values of <0.05, 0.01 and 0.001 are indicated with *, ** and ***, respectively