β-Mannanase (Man26A) and α-galactosidase (Aga27A) synergism – A key factor for the hydrolysis of galactomannan substrates

Abstract

This study investigated the behavior of mannan-degrading enzymes, specifically focusing on differences with respect to their substrate specificities and their synergistic associations with enzymes from different glycoside hydrolase (GH) families. Galactosidases from Cyamopsis tetragonolobus seeds (Aga27A, GH27) and Aspergillus niger (AglC, GH36) were evaluated for their abilities to synergistically interact with mannanases from Clostridium cellulovorans (ManA, GH5) and A. niger (Man26A, GH26) in hydrolysis of guar gum and locust bean gum. Among the mannanases, Man26A was more efficient at hydrolyzing both galactomannan substrates, while among the galactosidases; Aga27A was the most effective at removing galactose substituents on both galactomannan substrates and galactose-containing oligosaccharides. An optimal protein mass ratio of glycoside hydrolases required to maximize the release of both reducing sugar and galactose residues was determined. Clear synergistic enhancement of locust bean gum hydrolysis with respect to reducing sugar release was observed when both mannanases at 75% enzyme dosage were supplemented with 25% enzyme protein dosage of Aga27A. At a protein ratio of 75% Man26A to 25% Aga27A, the presence of Man26A significantly enhanced galactose release by 25% Aga27A (2.36 fold) with locust bean gum, compared to when Aga27A was used alone at 100% enzyme protein dosage. A dosage of Aga27A at 75% and ManA at 25% protein content liberated the highest reducing sugar release on guar gum hydrolysis. A dosage of Man26A and Aga27A at 75–25% protein content, respectively, liberated reducing sugar release equivalent to that when Man26A was used alone at 100% protein content. From the findings obtained in this study, it was observed that the GH family classification of an enzyme affects its substrate specificity and synergistic interactions with other glycoside hydrolases from different families (more so than its EC classification). The GH26 Man26A and GH27 Aga27A enzymes appeared to be more promising for applications that involve the hydrolysis of galactomannan containing biomass. This method of screening for maximal compatibility between various GH families can ultimately lead to a more rational development of tailored enzyme cocktails for lignocellulose hydrolysis.