Cysteine-Mediated Cyclic Metabolism Drives the Microbial Degradation of Keratin

Keratinase is a key enzyme to degrade keratin. However, the extremely low efficiency of keratinase hydrolyzing keratin after being separated from living cells is still the bottleneck of its application. Living cells seem to provide synergistic factors for the efficient catalysis of keratinase. To this end, we analyzed the role of the metabolic activity of living cells in the hydrolysis of feather keratin by keratinase. Here, studies have shown that sulfite is the key to switch on the catalytic procedure of keratinase, and cysteine is the bridge for living cells to control this process. Cysteine catabolism mediated by an intracellular detoxification mechanism produces sulfite and is secreted to promote the hydrolysis of keratin by keratinase. Then, the cysteine released by keratin hydrolysis will enter the cell and continue to be converted into sulfite through catabolism. These two processes form a perpetual chain reaction for the adequate hydrolysis of keratin. Furthermore, we confirmed that loading this self-circulation synergistic catalysis system into keratinase-secreting cells can significantly enhance their keratin hydrolysis capacity. This work demonstrated the missing link of keratinase-catalyzed keratin hydrolysis and obtained engineered strains with improved hydrolysis capacity.