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. 2021 Feb 28;2:6. doi: 10.1186/s43556-021-00026-3

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© The Author(s) 2021

Open AccessThis 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 licence, and indicate if changes were made. The images or other third party material in this article are included in the article's Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article's Creative Commons licence 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 licence, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 1 — Electrophysiological properties of the engineered M2MspA-N91H and scheme of neurotransmitters detection. a Side-view (left) and top-view (right) of M2MspA-N91H structure modeled by SWISS-MODEL. b SDS-PAGE analysis of M2MspA-N91H and M2MspA. N91H represents M2MspA-N91H, and M2 represents M2MspA. c Typical current traces of blank, M2MspA and M2MspA-N91H nanopore inserting into lipid bilayer in 1 M KCl, pH 7.5, 50 mV. d I-V curves of M2MspA-N91H and M2MspA at scanning potential from − 150 to 150 mV. e Conductance histograms of M2MspA-N91H and M2MspA nanopore inserting into lipid bilayer in 1 M KCl, pH 7.5 (n = 35). f Experimental setup. The mutant protein M2MspA-N91H is incorporated into lipid bilayer from the cis (grounded) side of the setup. Cu²⁺ and neurotransmitters are added to trans and cis side, respectively, which both move towards the constriction region of M2MspA-N91H under a positive potential. g Ionization structures of three neurotransmitters: glutamate, dopamine and norepinephrine. h The principle of detection of neurotransmitters. Cu²⁺ non-covalently binds to the two nearby histidine residues at the constriction region of M2MspA-N91H firstly, then neurotransmitters which can interact with Cu²⁺ are detected. i Idealized current signals caused by different kinds of neurotransmitters binding reversibly to the Cu²⁺-M2MspA-N91H complex