An exo-尾-(1鈫?)-d-galactanase from Streptomyces sp. provides insights into type II arabinogalactan structure

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• 作者：Naomi X.-Y. Ling^a ; Joanne Lee^a ; Miriam Ellis^a ; Ming-Long Liao^a ; Shaio-Lim Mau^a ; David Guest^c ; Peter H. Janssen^d ; Pavol Ková ; č ; ^e ; Antony Bacic^a ; ^b ; Filomena A. Pettolino^a ; ^{Filomena.Pettolino@csiro.au}
• 关键词：尾-d-Galactanases ; Arabinogalactan-protein ; Streptomyces sp. ; De-arabinosylated gum arabic ; CAZy family GH 43
• 刊名：Carbohydrate Research
• 出版年：2012
• 期刊代码：15_00086215
• 类别：ch
• 出版时间：1 May, 2012
• 卷：352
• 期：Complete
• 页码：70-81
• 文件大小：1139 K

摘要

An exo-尾-(1鈫?)-d-galactanase (SGalase1) that specifically cleaves the 尾-(1鈫?)-d-galactan backbone of arabinogalactan-proteins (AGPs) was isolated from culture filtrates of a soil Streptomyces sp. Internal peptide sequence information was used to clone and recombinantly express the gene in E. coli. The molecular mass of the isolated enzyme was 鈭?5 kDa, similar to the 48.2 kDa mass predicted from the amino acid sequence. The pI, pH and temperature optima for the enzyme were 鈭?.45, 3.8 and 48 掳C, respectively. The native and recombinant enzymes specifically hydrolysed 尾-(1鈫?)-d-galacto-oligo- or poly-saccharides from the upstream (non-reducing) end, typical of an exo-acting enzyme. A second homologous Streptomyces gene (SGalase2) was also cloned and expressed. SGalase2 was similar in size (47.9 kDa) and enzyme activity to SGalase1 but differed in its pH optimum (pH 5). Both SGalase1 and SGalase2 are predicted to belong to the CAZy glycosyl hydrolase family GH 43 based on activity, sequence homology and phylogenetic analysis. The K_m and V_max of the native exo-尾-(1鈫?)-d-galactanase for de-arabinosylated gum arabic (dGA) were 19 mg/ml and 9.7 渭mol d-Gal/min/mg protein, respectively. The activity of these enzymes is well suited for the study of type II galactan structures and provides an important tool for the investigation of the biological role of AGPs in plants. De-arabinosylated gum arabic (dGA) was used as a model to investigate the use of these enzymes in defining type II galactan structure. Exhaustive hydrolysis of dGA resulted in a limited number of oligosaccharide products with a trisaccharide of Gal₂GlcA₁ predominating.