Enhanced activity and stability of protein-glutaminase by Hofmeister effects

Protein-glutaminase (PG) catalyzes the deamidation of only the side-chain amide group of glutamine (Gln) residues in proteins, leading to improved protein functionalities such as water solubility, emulsifying properties, and foaming ability. However, the application of PG to food processing is limited because of its low stability and low activity. In this study, the effects of 32 Hofmeister salts on enzyme activity and stability were investigated. The results showed that the activation or stabilization of PG approximately followed the same order as the Hofmeister series. Notably, compared with the treatment without salts, the addition of 1.0 M sodium carbonate (Na2CO3) enhanced the catalytic efficiency by 9.7-fold. Additionally, the presence of Na2CO3 extended the half-life (t1/2) of PG by 8.5-, 4.6-, and 2.1-fold at 50, 60, and 70 °C, respectively. Moreover, a bell-shaped correlation was observed between the catalytic efficiency (kcat/Km) value and the Jones-Dole viscosity B-coefficient B–-B+ value, suggesting it could be a good indicator to quantify the effect of Hofmeister salts on PG activity. Importantly, our data show that Hofmeister salts enhance the solubility ratio and velocity of food proteins by PG. Therefore, the combination of Hofmeister salts and PG could offer a great promise for food processing.