Functional comparison of versatile carbohydrate esterases from families CE1, CE6 and CE16 on acetyl-4-O-methylglucuronoxylan and acetyl-galactoglucomannan.

ABSTRACT

BACKGROUND: The backbone structure of many hemicelluloses is acetylated, which presents a challenge when the objective is to convert corresponding polysaccharides to fermentable sugars or else recover hemicelluloses for biomaterial applications. Carbohydrate esterases (CE) can be harnessed to overcome these challenges. METHODS: Enzymes from different CE families, AnAcXE (CE1), OsAcXE (CE6), and MtAcE (CE16) were compared based on action and position preference towards acetyl-4-O-methylglucuronoxylan (MGX) and acetyl-galactoglucomannan (GGM). To determine corresponding positional preferences, the relative rate of acetyl group released by each enzyme was analyzed by real time 1H NMR. RESULTS: AnAcXE (CE1) showed lowest specific activity towards MGX, where OsAcXE (CE6) and MtAcE were approximately four times more active than AnAcXE (CE1). MtAcE (CE16) was further distinguished by demonstrating 100 times higher activity on GGM compared to AnAcXE (CE1) and OsAcXE (CE6), and five times higher activity on GGM than MGX. Following 24h incubation, all enzymes removed between 78 and 93% of total acetyl content from MGX and GGM, where MtAcE performed best on both substrates. MAJOR CONCLUSIONS: Considering action on MGX, all esterases showed preference for doubly substituted xylopyranosyl residues (2,3-O-acetyl-Xylp). Considering action on GGM, OsAcXE (CE6) preferentially targeted 2-O-acetyl-mannopyranosyl residues (2-O-acetyl-Manp) whereas AnAcXE (CE1) demonstrated highest activity towards 3-O-acetyl-Manp positions; regiopreference of MtAcE (CE16) on GGM was less clear. GENERAL SIGNIFICANCE: The current comparative analysis identifies options to control the position of acetyl group release at initial stages of reaction, and enzyme combinations likely to accelerate deacetylation of major hemicellulose sources.