一种新的抗菌药物靶标蛋白质(3，4-二羟基-2-丁酮-4-磷酸合成酶)的克隆、表达、纯化及酶活性鉴定

Cloning and characterization of a new antibacterial target，3，4-Dihydroxy-2-butanone-4-phosphate synthase

摘要:

摘要:【目的】核黄素(vitamin B12，riboflavin)是辅因子黄素腺嘌呤二核苷酸(flavin adenine dinucleotide，FAD)和黄素单核苷酸(flavin mononucleotide，FMN)的前体物，对生物体的生物合成至关重要。如果细菌不能够从外界摄取足够的黄素(flavin)就需要自身合成核黄素以维持菌体的生存与增殖。3，4-二羟基-2-丁酮-4-磷酸合成酶(3，4-Dihydroxy-2-butanone-4-phosphate synthase，DHBPs)为核黄素生物合成途径中关键酶之一。在镁离子存在的情况下，DHBPs 将5-磷酸核酮糖(ribulose-5-phosphate，Ru5P)转换成3，4-二羟基-2-丁酮-4-磷酸(3，4-dihydroxy-2-Bu-tanone-4-Pho-sphate，DHBP) 和甲酸盐(formate)，生成的DHBP 为核黄素合成的必需原料之一。人类没有合成核黄素的相关途径，因此细菌参与合成核黄素的DHBPs 等相关酶就有望成为抗菌药物作用的靶位点。本课题通过对肺炎链球菌的DHBPs 进行克隆表达纯化与酶学性质鉴定，为开展其三维结构的解析和抗菌药物设计提供重要的工作基础。【方法】利用PCR 技术扩增DHBPs 基因，构建重组表达载体pW28-DHBPs。将其转入大肠杆菌(Escherichia coli) BL21 (DE3)中表达，用Ni 离子亲和层析及离子交换(DEAE)纯化获得有活性的DHBPs 后，进行酶学性质鉴定。【结果】酶切和测序证实成功构建了质 粒pW28-DHBPs，在E． coli BL21 中表达了可溶性DHBPs，纯化后获得了纯度为95% 的靶蛋白质，经分子筛分析DHBPs 在溶液中以二聚体形式存在。对DHBPs 进行酶学性质分析表明，在25℃、pH 为7. 5 和Mg2 + 存在的情况下，DHBPs 具有将5-磷酸核酮糖转换成DHBP 和甲酸盐的活性。【结论】第一次成功克隆并在E．coli BL21 中表达了一种肺炎链球菌合成核黄素的相关酶—DHBPs，纯化后的重组DHBPs 具有较好的5-磷酸核酮糖分解活性，这为解析其三维结构和基于结构进行的新一代抗菌药物设计提供重要的工作基础。

Abstract:

Abstract:［Objective］Riboflavin，called generally vitamin B12，is the precursor of cofactor flavin adenine dinucleotide (FAD) and flavin mononucleotide，which plays crucial roles in the biosynthesis of organisms． Bacteria need to synthesize riboflavin to maintain their survival and proliferation if they cannot obtain flavin from the surroundings．3，4-Dihydroxy-2-butanone-4-phosphate synthase (DHBPs) is one of the key enzymes in biosynthesis of riboflavin． In the presence of Mg2+，DHBPs can degrade ribulose-5-phosphate (Ru5P) into formate and 3，4-dihydroxy-2-butanone-4-phosphate (DHBP)． Potentially，these enzymes related to biosynthesis and metabolism of riboflavin，including DHBPs，may serve as the target for new antibacterial drug． In order to determine the three-dimensional structure and screen small molecule of inhibitor of DHBPs，we expressed and purified DHBPs from Streptococcus pneumonia (S.pn)，and characterized the activity of this enzyme． ［Method］DHBPs gene was amplified by PCR，and over-expression plasmid pW28-DHBPs was constructed． pW28-DHBPs was transformed into Escherichia coli BL21 (DE3) to express DHBPs; the recombinant protein was purified by nickel column and ion-exchange column． The enzymatic activity was tested using spectroscopy． ［Results］The plasmid of pW28-DHBPs was verified by restrictive enzyme digestion and sequencing． Soluble DHBPs was expressed in E． coli BL21，and purified with 95% purity． The result of size exclusion chromatography indicates that DHBPs was dimer in solution． Additionally，the recombinant protein has activity to hydrolyze Ru5P into formate and DHBP in the conditions of pH 7. 5 and 25℃ and in the presence of Mg2+．［Conclusions］DHBPs could be highly expressed in soluble form in E． coli BL21 strain，and the recombinant protein has activity to hydrolyze Ru5P．