Cooperative Effect of Multiple Domains in Copper Proteins Applied to H₂S Sensing

The revolutionary discovery by Abe & Kimura that H₂S exerts a beneficial role in human body has renewed interest in this small molecule, long known for its toxicity. Understanding the (bio)-reactivity of H₂S with biological and bioinorganic targets is therefore of increasing importance, yet studies on its interaction with nonheme metalloproteins remain limited. Here, we investigate the reactivity of HS^- with two natural multicopper proteins, SLAC and NiR. We demonstrate that SLAC, a two-domain blue-copper oxidase, can function as a multiwavelength, multireadout fluorescent sensor for H₂S in complex environments. Comparative studies on NiR support the proposed mechanism of H₂S recognition via selective reduction of copper centers. Finally, we benchmark the performance of these multicopper proteins against Cu-azurin, previously reported as a H₂S recognition element, highlighting the advantages of multicopper architectures in terms of sensitivity, selectivity, and reversibility. Our findings establish multicopper proteins as versatile platforms for H₂S sensing with potential applications in biomedical and environmental monitoring.