Expression, Characterization and Structure Analysis of a New GH26 Endo-β-1, 4-Mannanase (Man26E) from Enterobacter aerogenes B19

Production of mannooligosaccharides from orange peel waste with β-mannanase expressed in Trichosporonoides oedocephalis

A large quantity of orange peel waste (OPW) is generated per year, yet effective biorefinery methods are lacking. In this study, Trichosporonoides oedocephalis ATCC 16958 was employed for hydrolyzing OPW to produce soluble sugars. Glycosyl hydrolases from Paenibacillussp.LLZ1 which can hydrolyze cellulose and hemicellulose were mined and characterized, with the highest β-mannanase activity of 39.1 U/mg at pH 6.0 and 50 ℃. The enzyme was overexpressed in T. oedocephalis and the sugar production was enhanced by 16 %. The accumulated sugar contains 57 % value-added mannooligosaccharides by the hydrolysis of mannans. The process was intensified by a pretreatment combining H2O2 submergence and steam explosion to remove potential inhibitors. The mannooligosaccharides yield of 6.5 g/L was achieved in flask conversion and increased to 9.7 g/L in a 5-L fermenter. This study improved the effectiveness of orange peel waste processing, and provided a hydrolysis-based methodology for the utilization of fruit wastes.

Crystallization, structural characterization and kinetic analysis of a GH26 β-mannanase from Klebsiella oxytoca KUB-CW2-3

β-Mannanase (EC 3.2.1.78) is an enzyme that cleaves within the backbone of mannan-based polysaccharides at β-1,4-linked D-mannose residues, resulting in the formation of mannooligosaccharides (MOS), which are potential prebiotics. The GH26 β-mannanase KMAN from Klebsiella oxytoca KUB-CW2-3 shares 49-72% amino-acid sequence similarity with β-mannanases from other sources. The crystal structure of KMAN at a resolution of 2.57 Å revealed an open cleft-shaped active site. The enzyme structure is based on a (β/α)₈-barrel architecture, which is a typical characteristic of clan A glycoside hydrolase enzymes. The putative catalytic residues Glu183 and Glu282 are located on the loop connected to β-strand 4 and at the end of β-strand 7, respectively. KMAN digests linear MOS with a degree of polymerization (DP) of between 4 and 6, with high catalytic efficiency (k_cat/K_m) towards DP6 (2571.26 min^-1 mM^-1). The predominant end products from the hydrolysis of locust bean gum, konjac glucomannan and linear MOS are mannobiose and mannotriose. It was observed that KMAN requires at least four binding sites for the binding of substrate molecules and hydrolysis. Molecular docking of mannotriose and galactosyl-mannotetraose to KMAN confirmed its mode of action, which prefers linear substrates to branched substrates.