A Halophilic Aminopeptidase With Broad Substrate Specificity: Exploring Its Catalytic Potential and Application in...

Halophilic aminopeptidases with broad substrate specificity represent valuable biocatalysts for promoting protein hydrolysis in high-salt fermented foods. In this study, an M42 aminopeptidase from the halophilic archaeon, Haladaptatus litoreus, was identified and designated as AP_Hap. The optimal reaction conditions for AP_Hap were 2-2.5 M NaCl, a temperature of 60°C, and a pH of 7.5. It displayed robust activity and stability across a wide range of salinity, temperature, and pH conditions. AP_Hap demonstrated exceptional tolerance to both organic solvents and surfactants. In contrast to most characterized M42 aminopeptidases, AP_Hap exhibited a broad substrate spectrum, with the highest activity observed when using Leu-p-nitroaniline as the substrate. The V_max and K_m for AP_Hap were 5.28 µmol/min/mg and 0.59 mM, respectively. When applied for fish protein hydrolysis in hypersaline conditions, AP_Hap significantly increased the total free amino acid content, particularly enhancing the proportion of sweet and umami amino acids. To our knowledge, AP_Hap is the first halophilic and mesophilic M42 aminopeptidase characterized from the genus Haladaptus. These desirable properties indicated that AP_Hap has great potential for enhancing protein hydrolysis during the processing of high-salt fermented foods. PRACTICAL APPLICATION: The characteristics of AP_Hap conform with the demands of high-salt fermented food production, highlighting its potential as a biocatalyst for improving both process efficiency and product quality.