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. 2022 Jan 11;13:255. doi: 10.1038/s41467-021-27822-3

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© The Author(s) 2022

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. 4 — a A Xe-pressurized structure of GxtA shows the presence of Xe near the mononuclear iron-containing active site. The location of Xe was verified by calculation of anomalous maps, which are shown in purple mesh and contoured around Xe at 3.0σ. b An approximate 33-Å long tunnel connects the surface of GxtA to the non-heme iron-containing active site. This calculated tunnel overlaps with the position of Xe. The loops of GxtA (pink and teal) leave this tunnel open, whereas the loop of SxtT (gray) closes off this path. c The SxtT (gray) and GxtA (golden yellow) regions around the tunnel differ at several positions. The flexible loops are shown at low transparency to show the differences more clearly in tunnel lining residues. d Only low levels of activity are observed when ddSTX and β-STOH are combined with single (S232A, I237T), double (S232A/I237T, W214M/I237T), and chimeric (W214M/S232A/I237T) SxtT tunnel variants. Of note, there is no activity on STX using SxtT or any tunnel variant tested. In panel d, data was measured using n = 2 independent experiments. In all panels, ddSTX corresponds to dideoxysaxitoxin, β-STOH corresponds to β-saxitoxinol, and STX corresponds to saxitoxin. Source data are provided as a Source Data file.