Kim Dong Hyun, Kim Do Hyoung, Lee Sang-Hyun, Kim Kyoung Heon
Department of Biotechnology, Graduate School, Korea University, Seoul, 02841 South Korea.
Biotechnol Biofuels. 2018 Mar 14;11:64. doi: 10.1186/s13068-018-1059-2. eCollection 2018.
Laminarin is a potential biomass feedstock for the production of glucose, which is the most preferable fermentable sugar in many microorganisms by which it can be converted to biofuels and bio-based chemicals. Also, laminarin is a good resource as functional materials because it consists of β-1,3-glucosidic linkages in its backbone and β-1,6-glucosidic linkages in its branches so that its oligosaccharides driven from laminarin have a variety of biological activities. It is industrially important to be able to produce laminarioligosaccharides as well as glucose from laminarin by a single enzyme because the enzyme cost accounts for a large part of bio-based products. In this study, we investigated the industrial applicability of Bgl1B, a unique β-glucosidase from 2-40, belonging to the glycoside hydrolase family 1 (GH1) by characterizing its activity of hydrolyzing laminarin under various conditions.
Bgl1B was cloned and overexpressed in from 2-40, and its enzymatic activity was characterized. Similar to most of β-glucosidases in GH1, Bgl1B was able to hydrolyze a variety of disaccharides having different β-linkages, such as laminaribiose, cellobiose, gentiobiose, lactose, and agarobiose, by cleaving β-1,3-, β-1,4-, and β-1,6-glycosidic linkages. However, Bgl1B showed the highest specific activity toward laminaribiose with a β-1,3-glycosidic linkage. In addition, it was able to hydrolyze laminarin, one of the major polysaccharides in brown macroalgae, into glucose with a conversion yield of 75% of theoretical maximum. Bgl1B also showed transglycosylation activity by producing oligosaccharides from laminarin and laminaribiose under a high mass ratio of substrate to enzyme. Furthermore, Bgl1B was found to be psychrophilic, exhibiting relative activity of 59-85% in the low-temperature range of 2-20 °C.
Bgl1B can directly hydrolyze laminarin into glucose with a high conversion yield without leaving any oligosaccharides. Bgl1B can exhibit high enzymatic activity in a broad range of low temperatures (2-20 °C), which is advantageous for establishing energy-efficient bioprocesses. In addition, under high substrate to enzyme ratios, Bgl1B can produce high-value laminarioligosaccharides via its transglycosylation activity. These results show that Bgl1B can be an industrially important enzyme for the production of biofuels and bio-based chemicals from brown macroalgae.
海带多糖是生产葡萄糖的一种潜在生物质原料，葡萄糖是许多微生物中最理想的可发酵糖，可通过它转化为生物燃料和生物基化学品。此外，海带多糖是一种很好的功能材料资源，因为其主链由β-1,3-糖苷键组成，分支由β-1,6-糖苷键组成，因此由海带多糖衍生的寡糖具有多种生物活性。能够通过单一酶从海带多糖中生产海带寡糖和葡萄糖在工业上具有重要意义，因为酶成本在生物基产品中占很大一部分。在本研究中，我们通过表征其在各种条件下水解海带多糖的活性，研究了来自2-40的一种独特的β-葡萄糖苷酶Bgl1B的工业适用性。
Bgl1B在2-40中被克隆并过量表达，并对其酶活性进行了表征。与GH1中的大多数β-葡萄糖苷酶类似，Bgl1B能够通过切割β-1,3-、β-1,4-和β-1,6-糖苷键来水解具有不同β-键的多种二糖，如海带二糖、纤维二糖、龙胆二糖、乳糖和琼胶二糖。然而，Bgl1B对具有β-1,3-糖苷键的海带二糖表现出最高的比活性。此外，它能够将褐藻中的主要多糖之一海带多糖水解为葡萄糖，转化率达到理论最大值的75%。在底物与酶的高质量比下，Bgl1B还通过从海带多糖和海带二糖产生寡糖而表现出转糖基化活性。此外，发现Bgl1B是嗜冷的，在2-20°C的低温范围内表现出59-85%的相对活性。
Bgl1B可以直接将海带多糖高效水解为葡萄糖，且不留下任何寡糖。Bgl1B在广泛的低温范围（2-20°C）内可表现出高酶活性，这有利于建立节能生物工艺。此外，在高底物与酶比例下，Bgl1B可通过其转糖基化活性生产高价值的海带寡糖。这些结果表明，Bgl1B可能是一种用于从褐藻生产生物燃料和生物基化学品的重要工业酶。
