tailieunhanh - Báo cáo Y học: The b-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

TheAspergillus nigerb-1,4-endogalactanase encoding gene (galA) was cloned and characterized. The expression ofgalA in A. nigerwas only detected in the presence of sugar beet pectin,D-galacturonic acid andL-arabinose, suggesting that galAis coregulatedwithboth thepectinolyticgenes aswell as the arabinanolytic genes. The corresponding enzyme, endogalactanase A (GALA), contains both active site resi-dues identified previously for thePseudomonas fluorescens b-1,4-endogalactanase. | Eur. J. Biochem. 269 4985-4993 2002 FEBS 2002 doi The b-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 Ronald P. de Vries Lucie Paíenicová1 Sandra W. A Hinz2. Harrv C M. Kester1. Gerrit Beldman2 B WHBBWBBBBB B B Jacques Ab Eb Benen1 and Jaap Visser1 1Molecular Genetics of Industrial Microorganisms and 2Food Chemistry Wageningen University Wageningen The Netherlands 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 kDa and a pH optimum between 4 and . Incubations of arabinogalactans of potato onion and soy with GALA resulted initially in the release of D-galactotriose and D-galactotetra-ose whereas prolonged incubation resulted in D-galactose and D-galactobiose predominantly. MALDI-TOF analysis revealed the release of L-arabinose substituted D-galacto-oligosaccharides 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. Keywords Aspergillus niger b-1 4-endogalactanase galac-turonic acid expression galactan degradation. Endogalactanases are involved in the degradation of plant cell wall polysaccharides in particular pectin. Two types of arabinogalactan side chains are