固定化分子伴侣GroE促进变性溶菌酶复性的研究

利用重组大肠杆菌表达制备了分子伴侣GroE(GroEL和GroES),研究了GroE以及GroEL辅助变性溶菌酶复性的作用。结果表明,不仅游离GroEL单独作用可使溶菌酶复性收率达到90%以上,而且固定化GroEL亦可有效地促进蛋白质复性,最佳复性温度为37℃,最佳pH值范围为6～8,复性酶的活性收率在85%以上。另外,固定化GroEL可反复回收利用,表明固定化GroEL有可能在实际生物下游过程中得到应用。     

技术与方法理性设计改造牛肠激酶的热稳定性

以牛肠激酶作为研究对象,利用理性设计的方法提高其热稳定性。首先通过分子动力学模拟软件Gromacs v 4.5.5,FlexService以及B-FITTER软件预测出了肠激酶的柔性区Fragment 64～69,Fragment 85～90;然后结合β-转角序列统计学信息以及引入位置原有的残基不参与形成氢键的原则,确立了3个突变位点S67P,R87P以及Y136P;通过Quik Change^TM 定点突变的方法引入突变位点,并进行了酶热稳定性分析。结果表明,R87P突变体酶的失活半衰（t_1/2）和T₅₀¹⁰ 较野生型分别提高了3.1 min和11.8℃,同时,动力学常数（K_m/k_cat）测定结果显示酶活未受到显著影响。该策略有潜力应用于其他工业酶分子的热稳定性改造,为推动生物酶的工业化应用奠定基础。     

牛肠激酶轻链基因的克隆及其在大肠杆菌中的融合表达

为克隆表达牛肠激酶（enterokinase）轻链(EKL)编码基因,以期应用于融合蛋白的切割与纯化,从市售北方黄牛十二指肠组织中提取总RNA,以RT-PCR方法扩增其cDNA片段,将此片段克隆于pUCmT载体中,经过特异性限制性内切酶酶切分析片段正确后,进行全序列分析。结果表明,克隆的cDNA与GenBank上的序列相比完全一致,得到了编码正确的牛肠激酶轻链基因全序列。随后,将目的基因片段插入pET39b中,构建了融合型表达载体pET39b-EKL,转化大肠杆菌BL21(DE3),用IPTG诱导表达。所获得的pET39b-EKL经过酶切鉴定和测序,证实其插入方向、读码框架正确,所表达重组蛋白经SDS-PAGE分析,相对分子量为65 kDa,表达量达28%,通过镍亲和层析纯化得到融合蛋白DsbA-rEKL的单一条带。该粗酶经脱盐后在适宜的缓冲体系中21℃温育过夜,显示出较高的自催化切割活性,为进一步进行重组牛肠激酶活性的研究及应用奠定了基础。 Abstract:The objective of the study was to obtain the gene of bovine enterokinase light chain,which would be used in the cleavage and purification of fusion proteins．The fragment of bovine enterokinase light chain cDNA was obtained by RT-PCR from a sold bovine′s duodenal mucosa, then cloned into the pUCmT cloning vector and sequenced.Compared with the sequence deposited in GenBank,the cloned gene sequence is correct.Then the interested gene fragment was inserted into the pET39b expression plasmid.The recombinant vector pET39b-EKL was transformed into E.coli BL21(DE3) and induced by IPTG.It was confirmed that the nucleotide sequence was correct on the conjunction site between the recombinant DNA 5′terminal multi-cloning site and recombinant fragment after the analysis of the nucleotide sequence.SDS-PAGE analysis indicated that target product was about 65 kDa which occupied 28% of the total protein.A pure fusion protein was obtained by nickel chelating chromatogram using His*Binding Resin.After desalting and changing buffer,the crude kinase was incubated at 21℃ overnight and demonstrated a high autocatalytic cleavage activity.This investigation would be able to lay a foundation for enterokinase activity research and farther application of expression products on a large scale.