Azurin and HS–: Towards Implementation of a Sensor for HS– Detection

Hydrogen sulfide (H2S) is an important biological messenger, which recently joined nitric oxide (NO) and carbon monoxide (CO) as an endogenously produced gasotransmitter. This discovery resulted in a renewed interest towards H2S and, in particular, in its reactivity with biological and bioinorganic targets. However, in the scientific literature studies exploring the reactivity of H2S/HS– with non-heme proteins are rare. In this work, we studied the interaction of HS– with the natural metalloprotein Cu-azurin and its cobalt variant via UV-Vis, fluorescence, and EPR spectroscopy, as well as X-ray diffraction. Interaction of HS– significantly enhances the fluorescence emission of fluorescently labelled copper azurin in buffered solutions and at physiological pH. In contrast, fluorescently labelled cobalt azurin undergoes a fluorescence quenching in the presence of HS– in line with the changes observed in the absorption spectrum of the construct. The results highlight the potential of azurin for implementation in a fast and simple HS– sensor.