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Lysine–cysteine redox switches with NOS bridges regulate enzyme function
Submitter: Ute Curth
Authors: Marie Wensien, Fabian Rabe von Pappenheim, Lisa-Marie Funk, Patrick Kloskowski, Ute Curth, Ulf Diederichsen, Jon Uranga, Jin Ye, Pan Fang, Kuan-Ting Pan, Henning Urlaub, Ricardo A. Mata, Viktor Sautner, Kai Tittmann
Corresponding Author: Ute Curth
Title: Lysine–cysteine redox switches with NOS bridges regulate enzyme function
Contribution Type: Full Talk
Selected for Presentation Yes
Abstract: In the transaldolase enzyme of Neisseria gonorrhoeae, we discovered a covalent crosslink between a cysteine and a lysine residue with an NOS bridge that serves as an allosteric redox switch1. High resolution X-ray structure analysis of the protein in the oxidized and reduced state revealed a loaded-spring mechanism that involves a structural relaxation resulting in an increase in enzymatic activity by more than one order of magnitude upon reduction. This reversible redox switch is highly conserved in related orthologues of other members of the Neisseriaceae.

Searching the Protein Data Bank for structures with unexplained electron density between nitrogen atoms of lysine and sulfur atoms of neighboring cysteine residues revealed that NOS bridges occur in various protein families across all domains of life and that they are often located at catalytic or regulatory hotspots. Moreover, in some proteins, a single lysine forms NOS bridges with two cysteine residues simultaneously, resulting in a branching SONOS bridge.

Such an SONOS bridge is found, for instance, in the main protease of SARS-CoV-2 (Mpro)2. In this case, oxidation leads to the formation of an SONOS bridge that is involved in the dissociation of enzymatically active Mpro dimers to produce inactive monomers. The accompanying conformational change protects the catalytic cysteine from oxidative damage as it might occur in vivo from reactive oxygen species produced by the host to defend against the pathogen. Exposure to reducing conditions, however, fully restores the dimeric state and the enzymatic activity of Mpro, indicating a reversible redox switch.

[1] Wensien, M., F. R. von Pappenheim, L. M. Funk, P. Kloskowski, U. Curth, U. Diederichsen, J. Uranga, J. Ye, P. Fang, K. T. Pan, H. Urlaub, R. A. Mata, V. Sautner and K. Tittmann (2021). Nature 593(7859): 460-464.

[2] Funk, L.-M., G. Poschmann, A. Chari, F. R. von Pappenheim, K.-M. Stegmann, A. Dickmanns, N. Eulig, M. Wensien, E. Paknia, G. Heyne, E. Penka, A. R. Pearson, C. Berndt, T. Fritz, S. Bazzi, J. Uranga, R. A. Mata, M. Dobbelstein, R. Hilgenfeld, U. Curth and K. Tittmann (2022). bioRxiv: 2022.2004.2018.487732.