中文摘要：

糖苷水解酶（GH）通常包含一个催化模块和各种非催化区（NCR）。然而，在NCR的催化模块的影响大部分还不清楚除了碳水化合物结合模块（CBMS）。agag4是βGH16内的海洋菌Flammeovirga sp. my04琼胶降解酶。酶是由一个额外的糖结合肽在催化模块，不可预测的信任但功能在NCR的未知序列，这是酶序列的新特点。在这项研究中，我们删除了NCR的序列，表达截短的基因，agag4-t140一个140个氨基酸的肽的C-末端，在大肠杆菌中的表达。纯化和复性后，trtmcated琼胶酶的ragag4-t140保留相同的催化温度和pH值ragag4。结合荧光标记，高效液相色谱法和质谱技术，我们确定的ragag4-t140作为新琼脂四糖和neoagarohexaose琼脂糖降解最终产物，随着1.53：1最终摩尔比和大约70%的转化率，这是类似于那些ragag4。然而，ragag4-t140截断琼胶酶显著降低蛋白质溶解度的15倍和35倍的增加，酶活性。对ragag4-t140低聚糖生产的，ragag4产生等摩尔重量约25倍。这项研究提供了一些见解的NCR对琼胶酶的生化特性和agag4意味着提高GH酶性质的一些新策略。

英文摘要：

A Glycoside hydrolase （GH） typically contains one catalytic module and varied non-catalytic regions （NCRs）. However, effects of the NCRs to the catalytic modules remain mostly unclear except the carbohydrate-binding modules （CBMs）. AgaG4 is a GH16 endo-β-agarase of the agarolytic marine bacterium Flammeovirga sp. MY04. The enzyme consists of an extra sugar-binding peptide within the catalytic module, with no predictable CBMs but function-unknown sequences in the NCR, which is a new characteristic of agarase sequences. In this study, we deleted the NCR sequence, a 140-amino acid peptide at the C-terminus and expressed the truncated gene, agaG4-T140, in Escherichia coli. After purification and refolding, the trtmcated agarase rAgaG4-T140 retained the same catalytic temperature and pH value as rAgaG4. Using combined fluorescent labeling, HPLC and MS/MS techniques, we identified the end-products of agarose degradation by rAgaG4-T140 as neoagarotetraose and neoagarohexaose, with a final molar ratio of 1.53：1 and a conversion ratio of approximately 70%, which were similar to those of rAgaG4. However, the truncated agarase rAgaG4-T140 markedly decreased in protein solubility by 15 times and increased in enzymatic activities by 35 times. The oligosaccharide production of rAgaG4-T140 was approximately 25 times the weight of that produced by equimolar rAgaG4. This study provides some insights into the influences of NCR on the biochemical characteristics of agarase AgaG4 and implies some new strategies to improve the properties of a GH enzyme.