基于金属有机沸石咪唑骨架的固定化细胞的制备及其在丙谷二肽制备中的应用

Immobilizing engineered Escherichia coli cells into zeolitic imidazolate framework 8 for efficient biosynthesis of Ala-Gln

摘要:

来源于鞘氨醇杆菌(Sphingobacterium siyangensis)中的α-氨基酸酯酰基转移酶(α-amino acid ester acyltransferase, SAET),是目前发现的丙谷二肽催化合成能力最高的酶之一,能够以非保护的l-丙氨酸甲酯盐酸盐、l-谷氨酰胺合成l-丙氨酰-l-谷氨酰胺[即丙谷二肽(l-alanyl-l-glutamine, Ala-Gln)]。为了解决其在催化过程中的稳定问题,本研究在水相体系中采用"一步法"快速制备固定化细胞(SAET@ZIF-8),在构筑金属有机沸石咪唑骨架结构(ZIF-8)的同时,将表达有SAET的大肠杆菌(Escherichia coli)包裹在其内部空间中。在此基础上,对其结构、催化活性和重复使用性及储存稳定性等催化性能进行探究。结果表明,通过该方法制备的SAET@ZIF-8纳米颗粒与文献报道的ZIF-8材料的形貌基本相同,细胞的引入没有明显改变ZIF-8的形貌。重复使用7次后,SAET@ZIF-8仍能保持67%左右的初始酶活;室温下放置4 d时,固定化酶还保留有50%左右的初始酶活,表明SAET@ZIF-8具有较好的重复使用及储存稳定性。将SAET@ZIF-8用于丙谷二肽的催化实验中,当反应30 min后丙谷二肽的浓度达到62.83 mmol/L (13.65 g/L),时空产率达到0.455 g/(L·min),相对于谷氨酰胺的转化率为62.83%。以上结果表明,基于金属有机沸石咪唑骨架的固定化细胞是一种高效制备丙谷二肽的方法策略。

Abstract:

The α-amino acid ester acyltransferase (SAET) from Sphingobacterium siyangensis is one of the enzymes with the highest catalytic ability for the biosynthesis of l-alanyl-l-glutamine (Ala-Gln) with unprotected l-alanine methylester and l-glutamine. To improve the catalytic performance of SAET, a one-step method was used to rapidly prepare the immobilized cells (SAET@ZIF-8) in the aqueous system. The engineered Escherichia coli (E. coli) expressing SAET was encapsulated into the imidazole framework structure of metal organic zeolite (ZIF-8). Subsequently, the obtained SAET@ZIF-8 was characterized, and the catalytic activity, reusability and storage stability were also investigated. Results showed that the morphology of the prepared SAET@ZIF-8 nanoparticles was basically the same as that of the standard ZIF-8 materials reported in literature, and the introduction of cells did not significantly change the morphology of ZIF-8. After repeated use for 7 times, SAET@ZIF-8 could still retain 67% of the initial catalytic activity. Maintained at room temperature for 4 days, 50% of the original catalytic activity of SAET@ZIF-8 could be retained, indicating that SAET@ZIF-8 has good stability for reuse and storage. When used in the biosynthesis of Ala-Gln, the final concentration of Ala-Gln reached 62.83 mmol/L (13.65 g/L) after 30 min, the yield reached 0.455 g/(L·min), and the conversion rate relative to glutamine was 62.83%. All these results suggested that the preparation of SAET@ZIF-8 is an efficient strategy for the biosynthesis of Ala-Gln.