Abstract

Fructose polysaccharides and oligosaccharides are gaining strong importance due to their beneficial effects on human health and their applications in the food, feed and pharmaceutical industries. Fructan synthesis has been characterised in a wide variety of bacteria and plants. Metagenomic DNA sequence data suggests that several archaeal strains also contain fructosyltransferase (ftf) genes in their genome sequences (www.cazy.org), and thus may be able to synthesise fructans. The archaeal ftf genes are predicted to encode glycoside hydrolase family 68 enzymes. These genes are of strong interest in view of their potential role in the synthesis of novel prebiotic compounds. In the present studies, we have expressed putative ftf gene of an archaeon Halalkalicoccus jeotgali B3T in E. coli. The recombinant enzyme produced water-insoluble polysaccharide using sucrose as a substrate. Analysis by ¹³C and ¹H NMR spectroscopy revealed the polysaccharide to be an inulin-type fructan polymer, depicting that the GH68 gene of H. jeotgali B3T codes for an inulosucrase enzyme. This is the first report on heterologous expression of an archaeal inulosucrase gene, which also provides conclusive evidence of the functional identity of this gene.

摘要

果糖多糖和低聚糖由于对人类健康的有益作用及其在食品，饲料和制药行业中的应用而变得越来越重要。在各种细菌和植物中都已表征了果聚糖的合成。元基因组DNA序列数据表明，一些古细菌菌株的基因组序列（www.cazy.org）中也包含果糖基转移酶（ftf）基因，因此可能能够合成果聚糖。预测古细菌ftf基因编码糖苷水解酶家族68种酶。考虑到它们在新型益生元化合物的合成中的潜在作用，这些基因引起了人们极大的兴趣。在本研究中，我们已经表达了古细菌的推定ftf基因jealtgali嗜盐链球菌B3T在大肠杆菌中。重组酶以蔗糖为底物产生了水不溶性多糖。分析由¹³ C和^1个H NMR光谱表明该多糖是一种菊粉型果聚糖聚合物，描绘的GH68基因H. jeotgali B3T代码用于inulosucrase酶。这是关于古细菌inulosucrase基因的异源表达的第一份报告，这也提供了该基因功能同一性的确凿证据。