We recently reported on the discovery of a lysine-cysteine redox switch in proteins with a covalent NOS bridge. Here, a systematic survey of the whole protein structure database discloses that NOS bridges are ubiquitous, hitherto overlooked redox switches in proteins of all domains of life and are found in diverse structural motifs and chemical variants. In several instances, lysines are observed in simultaneous linkage with two cysteines forming a SONOS bridge with a trivalent nitrogen, which constitutes the first native branching crosslink in proteins. In many proteins, the NOS switch contains a functionally essential lysine with direct roles in enzyme catalysis or binding of substrates, DNA or effectors linking lysine chemistry and redox biology as a novel regulatory principle. The NOS/SONOS switches are frequently found in proteins from human and plant pathogens including i.a. SARS-CoV-2 but also in many human proteins with established roles in gene expression, redox signaling and homeostasis in both physiological and pathophysiological conditions. Targeting, mimicking, controlling and engineering the NOS and SONOS redox switches appear to open novel avenues in drug, antiviral, antibiotic and herbicide development, in biocatalytic applications as well as in protein design and bioorganic chemistry.