Extremely Acidic β-1,4-Glucanase, CelA4, from Thermoacidophilic Alicyclobacillus sp A4 with High Protease Resistance and Potential as a Pig Feed Additive

An acidic endo-beta-1,4-glucanase, denoted CelA4 (similar to 48 kDa), was purified from thermoacidophilic Alicyclobacillus sp. A4. Two internal peptides of CelA4 showed strong sequence identity to the Alicyclobacillus acidocaldarius cellulase precursor and contained the conserved domain and catalytic region of glycoside hydrolase family 51 beta-1,4-glucanases, and the N-terminal and three other internal peptides had no close glucanase or cellulase relatives, suggesting that the enzyme might be novel. CelA4 had broad substrate specificity, exhibited maximum activity at 65 degrees C and pH 2.6, was stable over pH 1.8-7.6, and showed strong resistance to acidic and neutral proteases, notably pepsin. In comparison to the commercial endo-beta-1,3-1,4-glucanase, CelA4 was more stable, released more reducing Sugar from barley beta-glucan, and under simulated gastric conditions, decreased the viscosity of barley-.soybean feed to a greater extent. These properties make CelA4 a good candidate as a new commercial glucanase to improve the nutrient bioavailability of pig feed.