New redox-switches in proteins
by Marie Wensien
Date of Examination:2024-03-01
Date of issue:2024-04-26
Advisor:Prof. Dr. Kai Tittmann
Referee:Prof. Dr. Kai Tittmann
Referee:Prof. Dr. Ricardo A. Mata
Persistent Address:
http://dx.doi.org/10.53846/goediss-10464
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Abstract
English
Regulation of cellular pathways in response to the redox state of a cell is an important regulatory process. A well-established paradigm of redox-sensing is disulfide formation between two cysteine residues and cysteine mono-oxidation, as the sulfur atom of cysteines is highly susceptible to reactive oxygen species. The results of this work indicate the existence of a previously unknown redox regulatory element in proteins of all domains of life. This element, initially observed in crystal structures of the enzyme transaldolase from Neisseria gonorrhoeae (NgTAL), is a covalent crosslink that bridges a cysteine and a neighboring lysine residue via an additional oxygen atom, constituting a nitrogen-oxygen-sulfur (NOS) bridge. The involvement of the NOS cysteine residue in the redox sensitivity of NgTAL, observed in preceding experiments, hinted towards a redox regulatory function of this crosslink. This potential redox regulatory function of the NOS bridge was elucidated during this project. The results of the experiments conducted on NgTAL demonstrated the reversibility of the NOS bridge formation in vitro, which supports its potential biological function in redox signaling. The detection of the NOS bridge in solution, employing sulfur K-edge X-ray absorption spectroscopy, excluded the formation of the NOS bridge as a crystallization artifact and supports a potential in vivo existence of the crosslink. Functional and structural experiments conducted on the related transaldolase from Neisseria meningitidis also revealed the presence of the NOS bridge in this enzyme in vitro as a regulatory redox-switch, hinting towards a prevalence of the redox-switch among related homologues. A mining of the Protein Data Bank (PDB) identified hundreds of proteins, originating from all domains of life, that harbor an NOS bridge in crystallo. The widespread presence of NOS bridges in various proteins suggests the potential contribution of the crosslink in terms of function, structure and stability. In addition to NOS bridges, branching SONOS bridges, involving two cysteines and one lysine residue, were identified while searching the PDB for NOS bridges. Initial studies conducted on the main protease Mpro of SARS-CoV-2 also indicate a biological relevance for the first native branching crosslink between amino acid residues that we know of.
Keywords: NOS bridge; redox-switch; Transaldolase; Neisseria gonorrhoeae; SONOS bridge; SARS-CoV-2; redox regulation
