A protease-resistant exo-polygalacturonase from Klebsiella sp. Y1 with good activity and stability over a wide pH range in the digestive tract

Polygalacturonases are important feed and food additives. In the present study an exo-polygalacturonase gene (pgu B) was cloned from Klebsiella sp. Y1 CGMCC 4433 and expressed in Escherichia coli BL21 (DE3). pgu B encodes a 658-amino acid polypeptide belonging to Glycoside Hydrolase Family 28. The optimal pH and temperature of exo-PGU B activity were 6.0 and 40–50 °C, respectively. The enzyme exhibited >35% of maximum activity within the pH range of 2.0–12.0. Exo-PGU B or an exo-PGU B/ endo-polygalacturonase mixture reduced the viscosity of polygalacturonic acid (1.0%, w/v) by 15.6 and 39.4%, respectively. Under simulated alimentary tract conditions, exo-PGU B was very stable (>25% activity from pH 1.5 to 6.8) and active, releasing 53.7 and 109.6 μg of galacturonic acid from 400 to 800 μg of polygalacturonic acid, respectively. These properties make exo-PGU B a potentially valuable additive for applications in feed and food.