Fructansucrases (FSs), including inulosucrase (IS) and levansucrase (LS), are the members of the Glycoside Hydrolase family 68 (GH68) enzymes. IS and LS catalyze the polymerization of the fructosyl moiety from sucrose to inulin- and levan-type fructans, respectively. Lactobacillus-derived FSs have relatively extended N- and C-terminal sequences. However, the functional roles of these sequences in their enzymatic properties and fructan biosynthesis remain largely unknown. Limosilactobacillus reuteri (basionym: Lactobacillus reuteri) 121 could produce both IS and LS, abbreviated as Lare121-IS and Lare121-LS, respectively. In this study, it was found that the terminal truncation displayed an obvious effect on their activities and the N-terminal truncated variants, Lare121-ISΔ177-701 and Lare121-LSΔ154-686, displayed the highest activities. Melting temperature (T_m) and the thermostability at 50 °C were measured to evaluate the stability of various truncated versions, revealing the different effects of N-terminal on the stability. The average molecular weight and polymerization degree of the fructans produced by different truncated variants did not change considerably, indicating that N-terminal truncation had low influence on fructan biosynthesis. In addition, it was found that N-terminal truncation could also improve the activity of other reported FSs from Lactobacillus species.

果聚糖蔗糖酶 (FS)，包括菊糖蔗糖酶 (IS) 和果聚糖蔗糖酶 (LS)，是糖苷水解酶家族 68 (GH68) 酶的成员。IS 和 LS 分别催化蔗糖中的果糖基部分聚合为菊粉型和果聚糖型果聚糖。源自乳杆菌的FS 具有相对延长的 N 和 C 端序列。然而，这些序列在其酶学特性和果聚糖生物合成中的功能作用仍然未知。Limosilactobacillus reuteri（基名：Lactobacillus reuteri) 121 可以同时产生 IS 和 LS，分别缩写为 Lare121-IS 和 Lare121-LS。在本研究中，发现末端截短对其活性有明显影响，并且 N 末端截短的变体 Lare121-ISΔ177-701 和 Lare121-LSΔ154-686 显示出最高的活性。熔化温度 ( T _m) 和 50 °C 下的热稳定性以评估各种截短版本的稳定性，揭示 N 端对稳定性的不同影响。不同截短变体产生的果聚糖的平均分子量和聚合度没有显着变化，表明 N 端截短对果聚糖生物合成的影响很小。此外，发现 N 端截短还可以提高其他已报道的来自乳杆菌属的FS 的活性。