A gene encoding exo-β-(1→3)-galactanase from Irpex lacteus was cloned by reverse transcriptase-PCR. The deduced amino acid sequence showed high similarity with exo-β-(1→3)-galactanases from other sources. The molecular mass of the mature form was calculated to be 45,520 Da. The gene product expressed in Pichia pastoris specifically hydrolyzed β-(1→3)-galactooligosaccharides, as did other exo-β-(1→3)-galactanases. The recombinant enzyme showed high activity toward arabinogalactan-proteins (AGPs) from radish as well as β-(1→3)-galactan. Product analysis revealed that the enzyme released β-(1→6)-galactobiose, β-(1→6)-galactotriose, and α-l-arabinofuranosyl-(1→3)-β-galactosyl-(1→6)-galactose together with Gal from β-(1→3)-galactans attached with and without β-(1→6)-galactosyl branches prepared from acacia gum. These results indicate that the exo-β-(1→3)-galactanase from I. lacteus efficiently hydrolyzes β-(1→3)-galactan main chains of AGPs by bypassing β-(1→6)-galactosyl side chains.
通过
反转录酶-PCR 法克隆了一种编码外-β-(1→3)-
半乳聚糖酶的
基因。 推导出的
氨基酸序列与其他来源的外-β-(1→3)-
半乳聚糖酶高度相似。 经计算,其成熟形式的分子质量为 45 520 Da。 在 Pichia pastoris 中表达的
基因产物与其他外-β-(1→3)-
半乳聚糖酶一样,能特异性地
水解β-(1→3)-
半乳聚糖。
重组酶对萝卜中的阿拉伯半
乳糖蛋白(AGPs)以及β-(1→3)-半
乳糖具有很高的活性。 产物分析表明,从刺槐胶制备的附有或不附有β-(1→6)-半
乳糖基分支的β-(1→3)-半
乳糖中,该酶释放出β-(1→6)-半
乳糖生物糖、β-(1→6)-半
乳糖三糖和α-阿拉伯
呋喃糖基-(1→3)-β-半
乳糖基-(1→6)-半
乳糖以及Gal。 这些结果表明,I. lacteus 的外-β-(1→3)-
半乳聚糖酶通过绕过 β-(1→6)-半
乳糖基侧链,有效地
水解 AGP 的 β-(1→3)-半
乳糖主链。