Characterization of Guanine Deaminase from Kluyveromyces marxianus and Its Industrial Application to Reduce Guanine Content in Beer

Guanine deaminase (GDA) catalyzes the first step in purine catabolism by converting guanine to xanthine. Despite its significant role in the development of low-purine food, studies on GDA remain limited compared to other metabolic deaminases. To identify a GDA with high enzyme activity and appropriate optimum parameters, GDAs from Kluyveromyces lactis, Kluyveromyces marxianus, Lentilactobacillus kefiri, and Lactobacillus buchneri were heterologously expressed in Escherichia coli. The GDA from Kluyveromyces marxianus (KM-GD) showed the most potent enzyme activity (2.21 IU/mL) at 30 °C and pH 6.5, which is close to the pH of saccharified wort. Furthermore, analyzing the crystal structures of GDAs from different sources revealed that hydrogen bonds could enhance substrate affinity and strengthen enzyme activity. In addition, active pockets with an appropriate size may contribute to high enzyme activity. Finally, KM-GD helped reduce guanine by 80.33% in beer wort and by 80.00% in matured beer, thus suggesting its promise for industrial application in low-purine food production.