The β‐1,4‐endogalactanase A gene from Aspergillus niger is specifically induced on arabinose and galacturonic acid and plays an important role in the degradation of pectic hairy regions

Abstract

The Aspergillus niger b-1,4-endogalactanase encoding gene (galA) was cloned and characterized. The expression of galA in A. niger was only detected in the presence of sugar beet pectin, D-galacturonic acid and L-arabinose, suggesting that galA is coregulated with both the pectinolytic genes as well as the arabinanolytic genes. The corresponding enzyme, endogalactanase A (GALA), contains both active site residues identified previously for the Pseudomonas fluorescens b-1,4-endogalactanase.The galA gene was overexpressed to facilitate purification of GALA. The enzyme has a molecular mass of 48.5 kDa and a pH optimum between 4 and 4.5. Incubations of arabinogalactans of potato, onion and soy with GALA resulted initially in the release of D-galactotriose and D-galactotetraose, whereas prolonged incubation resulted in D-galactose and D-galactobiose, predominantly. MALDI-TOF analysis revealed the release of L-arabinose substituted D-galactooligosaccharides from soy arabinogalactan. This is the first report of the ability of a b-1,4-endogalactanase to release substituted D-galacto-oligosaccharides. GALA was not active towards D-galacto-oligosaccharides that were substituted with D-glucose at the reducing end. Genes encoding b-1,4-endogalactanase have been cloned from both bacteria and fungi [11][12][13][14][15]. Based on their derived amino acid sequence, the corresponding enzymes have been assigned to family 53 of the glycosyl hydrolases [16]. These enzymes have a retaining mechanism and for the Pseudomonas fluorescens b-1,4-endogalactanase the catalytic residues have been determined [11]. Recently, the Aspergillus aculeatus b-1,4-endogalactanase has been expressed in vivo in potato resulting in a 30% reduction of the galactosyl content of the pectin fraction of the cell walls [17].In this paper we describe the cloning, characterization and expression analysis of the A. niger galA gene, encoding b-1,4-endogalactanase. This is the first paper that describes the expression of this gene in detail and that compares the activity of the gene product, GALA, against arabinogalactans with a different degree of L-arabinose substitution.

Bifidobacterium longumEndogalactanase Liberates Galactotriose from Type I Galactans

“…Several fermentation studies showed that B. longum was able to use polymeric arabinogalactan as a substrate (9,11,42). This paper provides the first description of a polysaccharide-degrading enzyme from B. longum, further supporting the view that galactans can be fermented by bifidobacteria.…”

“…Since the genome sequence of Bifidobacterium longum recently became available (36), more information about Bifidobacterium glycolytic enzymes has been uncovered. The genome reveals that approximately 5% of all annotated genes are involved in the modification of carbohydrates.Several studies on in vitro fermentations of (␤13 4)-linked (arabino)galactans with different bifidobacteria show that mainly B. longum strains were able to grow on these arabinogalactans (9,11). This is consistent with the genome sequence of B. longum because it reveals the presence of many different putative enzymes potentially able to degrade arabinogalactans.…”

“…Several studies on in vitro fermentations of (␤13 4)-linked (arabino)galactans with different bifidobacteria show that mainly B. longum strains were able to grow on these arabinogalactans (9,11). This is consistent with the genome sequence of B. longum because it reveals the presence of many different putative enzymes potentially able to degrade arabinogalactans.…”

Characterization of the Erwinia chrysanthemi gan Locus, Involved in Galactan Catabolism

“…20% of the pectin oligosaccharides (45). Type I galactan is degraded by 1,4-␤-endogalactanases and 1,4-␤-exogalactanases (12). Galactanases are widely distributed into many plants.…”

“…They cause the solubilization of pectin oligosaccharides and seem to play a major role in ripening of fruits (29,32). 1,4-␤-Endogalactanase has been also isolated from microorganisms, including aerobic fungi belonging to the genus Aspergillus (12) and bacteria such as Bacillus subtilis (13), Pseudomonas fluorescens (9), and Thermotoga maritima (44).…”