【作者】 倪克奉；

【导师】 魏东芝；

【作者基本信息】 华东理工大学 ， 生物化学与分子生物学， 2014， 博士

【摘要】 生物催化在工业催化过程中发挥着重要的作用,而生物催化剂的固定化在其应用中扮演着重要角色。仿生黏附材料是基于海洋贻贝粘蛋白研究基础上人工合成的一种在水中具有粘附功能的材料。本课题利用邻苯二酚类衍生物所具有的粘附特性,通过合成不同类型的磁性固定化载体,对不同的生物催化剂进行固定化,并研究各个因素对固定化生物催化剂活力、稳定性的影响。具体的内容分为以下几个部分：(1)磁性壳聚糖纳米材料对ω-转氨酶J2315的固定化通过基因挖掘的方法筛选到一种新型的ω-转氨酶J2315,成功实现了该酶在大肠杆菌中的异源可溶表达,并对该酶的催化性质进行了鉴定,结果表明该酶的比活为8.6U/mg,具有S构型选择性,反应的最适pH为9.0,最适温度为40℃,该酶对芳香族胺类和芳香族醛类具有较好的催化活性。以邻苯二酚壳聚糖包裹的纳米四氧化三铁(CCS-IONPs)作为固定化载体,实现了ω-转氨酶J2315的高效固定化,此载体最大的载酶量为681.7mg蛋白/g载体,固定化酶活力回收率为87.5%。此外,固定化酶具有更好的稳定性和重复使用性。(2)产腈水解酶BCJ2315重组大肠杆菌的固定化及其应用利用邻苯二酚壳聚糖对细胞和纳米四氧化三铁相互交联,实现了重组大肠杆菌M15/BJ2315的固定化。固定化细胞活力回收率高,稳定性好,能通过磁分离实现重复使用。为了实现高浓度扁桃腈的转化,我们提出并优化了乙酸乙酯/水两相反应体系。在最优的条件下,成功的实现了1M扁桃腈在4h内的完全水解,产率为99%,ee值为95%。此外,利用固定化细胞在乙酸乙酯/水两相体系中连续多批次催化扁桃腈水解制备(R)-(-)-扁桃酸,在进行6批连续反应之后,(R)-(-)-扁桃酸的时空产率达到了40.9g·L-1.h-1,相对产量达到了24.1g·g-1。(3)聚多巴胺包裹的纳米四氧化三铁(PD-IONPs)司定化氧化葡萄糖酸杆菌的研究利用PD-IONPs作为固定化载体,通过材料表面的聚多巴胺与细胞粘附结合,进而引起细胞交联聚集实现细胞的固定化。在最优的条件下,每毫克材料能固定化21.3mg的湿菌体。通过此载体固定化氧化葡萄糖酸杆菌不影响其催化活性,并且赋予了固定化细胞良好的重复使用性。通过分析聚多巴胺与细胞表面结合的蛋白位点,发现与聚多巴胺结合的蛋白存在较多的赖氨酸、精氨酸或半胱氨酸,这些氨基酸残基所含有的氨基或巯基能与聚多巴胺的邻苯二酚基团通过共价键结合。(4)邻苯二酚基团粘附机理的研究为了揭示邻苯二酚基团与无机载体表面和生物大分子之间的粘附机理,我们以Fe3+和半胱氨酸作为模式研究对象,研究结果发现邻苯二酚基团能与Fe3+通过配位键形成络合物,而且其配位数由pH可逆的调控。此外,邻苯二酚基团与半胱氨酸反应结果表明邻苯二酚基团对巯基具有优先选择性。pH对邻苯二醌基团与氨基和巯基反应活性和选择性具有重要的影响。为了进一步研究邻苯二酚基团与生物大分子结合位点及其机理,我们采用邻苯二酚衍生化的PEG对脂肪酶LipK107进行修饰,通过定点突变的方法在脂肪酶的表面引入了半胱氨酸。结果揭示了邻苯二酚基团与蛋白的结合位点及其反应速率是由pH调控：在碱性条件下,邻苯二酚基团能与脂肪酶表面的氨基和巯基结合,反应速率快；而在中性的条件下,邻苯二酚基团与脂肪酶表面的巯基发生特异性的结合；在酸性条件下,邻苯二酚基团不能与脂肪酶结合。(5)磁性亲和纳米材料的制备及其应用基于邻苯二酚基团对金属离子和生物大分子的不同粘附机制,我们设计了两种磁性亲和纳米材料。通过还原性谷胱甘肽(GSH)与PD-IONPs表面的邻苯二酚基团反应制备GSH-PD-IONPs,此材料对GST标签融合蛋白具有较好的亲和性,成功的实现了GST融合的绿色荧光蛋白(GST-GFP)的分离纯化。此外,利用聚多巴胺包裹的磁性复合颗粒(PD-MNPs)络合镍离子后制备Ni2+-PD-MNPs,该材料对His标签融合蛋白展现出了很好的特异性,成功的用于分离纯化His标签融合的红色荧光蛋白(His-RFP)。同时,我们还利用该材料用于选择性固定化ω-转氨酶BJ110,结果表明该材料作为固定化载体能特异性的固定化细胞裂解液中的ω-转氨酶BJ110,固定化酶展现出了更好的比活力,还具有良好的稳定性和重复使用性。本课题所提出的基于仿生粘附材料的生物催化剂固定化技术,具有操作简便、固定化效率高、易于分离等优点,同时该技术具有普适性,能用于其它生物大分子,如酶、抗体、DNA等固定化。此外,通过对仿生粘附材料粘附机制进行揭示,为酶的理性固定化研究、蛋白质的修饰研究、酶的体外组装以及智能水凝胶的制备开拓了一条新型的技术解决路线。更多还原

【Abstract】 Biocatalysis is continuing to gain momentum and is now becoming a key component in process chemist. The immobilization of biocatalysts plays an important role in their applications. Recently, inspired by adhesive proteins secreted by marine mussels, various biomimetic adhesive materials which have strong adhesive ability under water were developed. In this study, we prepared different kinds of magnetic nanocomposites with catechol group on surface, and use to immobilize biocatalysts.The factors which dicatated the activity and stability of the immobilized biocatalysts were investigated, and the attachment mechanism of catechol was also determined. The detailed work was introduced as following:(1) Immobilization of ω-transaminase J2315via magnetic catecholic chitosanA novel co-transaminase from Burkholderia cenocepacia J2315has been recruited by homology search and the gene was cloned and functionally expressed in E.coli BL21. The specific activity of purified co-transaminase J2315was8.7U/mg. The enzyme had an optimal temperature of40℃, and an optimal pH of9.0, and it shows (S) enantio-selectivity and good activity towards aromatic aldehydes and aromatic amines. The magnetic catecholic chitosan, which carrying adhesive moieties with strong surface affinity, was prepared by simply coating of catecholic chitosan onto iron oxide nanoparticles, and used to immobilize ω-transaminase J2315. Under optimal conditions,87.5%of the available ω-transaminase J2315was immobilized on the composite, yielding an enzyme loading capacity as high as681.7mg/g. Furthermore, the valuation of enzyme activity showed that ω-transaminase J2315immobilized on CCS-IONPs displayed enhanced pH and thermal stability compared to free enzyme.(2) Immobilization of recombinant E.coli M15/BCJ2315via bio-inspired catecholic chitosanThe recombinant E.coli M15/BCJ2315which harbored a mandelonitrilase from Burkholderia cenocepacia J2315was immobilized via catecholic chitosan and functionalized with magnetism by iron oxide nanoparticles. The immobilized cells showed high activity recovery, enhanced stability and good operability in the enantioselective hydrolysis of mandelonitrile to (R)-(-)-mandelic acid. The ethyl acetate-water biphasic system was built and optimized. Under the optimal conditions, as high as1M mandelonitrile could be hydrolyzed within4h with a final yield and ee value of99%and95%, respectively. Moreover, the successive hydrolysis of mandelonitrile was performed by repeated use of the immobilized cells for6batches, giving a final productivity (g·L-1·h-1) and relative production (g-g-1) of40.9and38.9, respectively.(3) Immobilization of Gluconobacter oxydans using bio-adhesive magnetic nanoparticlesG.oxydans was immobilized via a synthetic adhesive biomimetic material inspired by the protein glues of marine mussels. This approach involves simple coating of a cell adherent polydopamine film onto magnetic nanoparticles, followed by conjugation of the polydopamine-coated nanoparticles to G.oxydans which resulted in cell aggregation. After optimization,21.3mg (wet cell weight) G.oxydans per milligram of nanoparticle was immobilized and separated with a magnet. Importantly, the immobilized cell showed high specific activity and good reusability. The membrane proteins on the surface of G.oxydans, which were attached by polydopamine, were separated via2D electrophoresis and analyzed by MALDI-TOF. The3D structure of these polydopamine-bound proteins revealed that these proteins were rich in Lys, Cys and Arg, which have reactive amine or thiol group toward catechol group.(4) Attachment mechanisms of catecholCoordination between catechol and Fe3+has been investigated, the results revealed the catechol-Fe3+ligands might have three coordination states and stoichiometrically dependent on the pH. The addition of Cys to catechol group suggested that the catechol group can react with thiol group preferentially. Furthermore, the reactivity of o-quinone group toward amine group was pH dependent. However, the thiol group can react with o-quinone under both acid and alkaline condition. The binding of catecholic PEG toward lipase was investigated.The results showed that, under neutral condition, the cathecol PEG can specifically couple to Cys residue which was introduced to the surface of enzyme molecule via site-directed mutagenesis. In alkaline condition, however, the catecholic PEG can react with both amine from Arg or Lys residues and thiol from Cys residue. Besides, the catecholic PEG cannot bind to lipase under acid condition.(5) Catechol-based magnetic affinity nanoparticles:preparation and applicationInspired by the adhesive mechanism of catechol group, which can coordinate with metal ion, as well as react with thiol group specifically under neutral condition, two catechol-based magnetic affinity nanoparticles were designed and synthesized via facile dopamine chemistry. The method involves in-situ coating of iron oxide nanoparticles with polydopamine, followed by conjugation of glutathione or Ni2+to the polydopamine film. The result revealed that GSH-PD-IONPs displayed high selectivity toward GST tagged proteins, and Ni2+-PD-MNPs showed exclusively specificity for His tagged proteins. In addition, the co-transaminase BJ110was selectively immobilized onto Ni2+-PD-MNPs without purification, the immobilized enzyme showed improved specific activity due the affinity property of Ni2+-PD-MNPs toward His tagged proteins. Furthermore, the immobilized enzyme exhibited enhanced stability and reusability.In conclusion, we present a novel approach for biocatalysts immobilization and is based on bio-inspired adhesive materials. It offers the potential advantages of low cost, easy separation, low diffusion resistance, and high efficiency. Furthermore, the approach is a convenient platform technique for immobilization of other biomolecules, such as enzymes, DNA and antibody. Our results may pave a new way to apply the catechol based technique for rational enzyme immobilization, protein modification, multi enzyme conjugation, and intelligent hydrogel preparation.更多还原