新型苏云金芽孢杆菌(−)γ-内酰胺酶基因的克隆与表达

【背景】γ-内酰胺是一种重要的医药中间体,其自身具备手性不利于药物合成,通过γ-内酰胺酶选择性拆分可实现光学纯γ-内酰胺的制备。【目的】挖掘来源苏云金芽孢杆菌(Bacillus thuringiensis)的γ-内酰胺酶基因,探索光学纯γ-内酰胺的制备工艺。【方法】通过"acetamidase/formamidase"关键词检索苏云金芽孢杆菌基因组,对检索出的两条序列进行异源表达,而后通过高效液相色谱法检测重组菌对γ-内酰胺的降解情况,确定克隆的基因是否为γ-内酰胺酶基因。利用构建的重组菌进行5L发酵、底物拆分、产物回收的生产应用尝试。【结果】构建的skA2重组菌株具有(-)γ-内酰胺酶活性,其在小规模制备生产中表现良好。【结论】A基因是一段未经报道的(-)γ-内酰胺酶基因,丰富了生产者的酶工具箱。构建的skA2菌株可以满足工业制备(+)γ-内酰胺的生产需求,为合成光学纯药物奠定坚实基础。     

高产(+)γ-内酰胺酶菌株的筛选与发酵产酶研究

从土壤中筛选获得高产(+)γ-内酰胺酶的微生物菌株,并鉴定和保藏为Delftia sp.CGMCC No.5755.对该Delfiia sp菌株的发酵产酶条件进行了研究,结果表明,最适发酵培养基为:蔗糖30 g/L,蛋白胨30 g/L,牛肉膏25 g/L,乙酰胺5 g/L,MgS04 1 g/L;最适发酵温度及初始pH分别为32℃和pH 7.0.该菌株在上述条件下发酵培养20 h,菌体生物量为16.0 g/L,(+)γ-内酰胺酶的酶活为692 U/L.采用Delftia sp.静息细胞对100 g/L的外消旋底物2-氮杂二环-[2.2.1]-庚烷-5-烯-3-酮(简称(±)γ-内酰胺)的水解拆分反应中,产物(-)γ-内酰胺光学纯度大于99.9％e.e.,转化率为53.7％.研究为生物催化法高效制备光学纯(+)γ-内酰胺提供了可行的途径.     

外源表达γ-内酰胺酶菌株的构建及发酵条件优化

我们构建了重组γ-内酰胺菌株E. coli BL21/pCDFDuet-γ-lactam,研究了发酵产γ-内酰胺酶的条件并进行了优化。研究结果表明,将pCDFDuet-1表达载体转化到含有γ-内酰胺酶基因的感受态E. coli中,得到重组γ-内酰胺菌株E. coli BL21/pCDFDuet-γ-lactam,通过IPTG诱导表达和HPLC检测发现,重组酶可以水解(+)γ-内酰胺,其e.e.值比E. coli BL21/γ-lactam表达提高了约30%。重组菌中(+)γ-内酰胺酶蛋白表观分子量为50 kD。对重组菌株发酵条件进行了初步研究,结果进一步表明,当选择碳源葡萄糖5 g/L、温度30℃、接种量4%、装液量100 mL/500 mL,转速180 r/min条件下,(+)γ-内酰胺酶含量最高,e.e.值约98%。本研究为探索出一条适合规模化生产的酶催化反应工艺提供参考,该工艺的意义不仅可以节约经济,而且对环境友好,可以替代化学工艺。     

产γ_内酰胺水解酶菌株的筛选及发酵条件研究

(-)γ-内酰胺是合成两种抗艾滋病药物(-)carbovir和(-)abacavir的重要原料,具有重要的应用价值,微生物酶法拆分( /-)γ-内酰胺生产(-)γ-内酰胺的方法具有良好的应用前景。以N-乙酰苯丙氨酸为唯一碳源,从土壤中筛选得到了69株具有酰胺水解酶活性的菌株,利用液相色谱分析方法确定了其中20株有较高的酰胺水解酶活性,利用手性色谱分析的方法进一步得到了一株具有较高立体选择性,能拆分( /-)γ-内酰胺而获得(-)γ-内酰胺的菌株L29-9,对该菌株的产酶培养基的碳、氮源及初始pH值等进行了研究。结果表明:当选择碳源柠檬酸2g/L、氮源酵母提取物5g/Lp、H 7.0、培养时间40h时,通过完整细胞转化,在30℃下经过12h的反应,产物(-)γ-内酰胺产率达40%,ee值99.5%。     

海因酶法制备D-对羟基苯甘氨酸的研究进展

D-对羟基苯甘氨酸(D-HPG)主要用于合成β-内酰胺类半合成抗生素,是国内最紧缺的医药中间体之一。微生物酶法是目前获得光学纯D-HPG的重要途径,微生物中起催化作用的主要是D-海因酶和N-氨甲酰水解酶。文章综述了产酶微生物的来源,酶的理化性质,以及培养条件的优化、基因工程、酶的固定化技术生产D-HPG的研究进展。     

革兰氏阴性菌中β-内酰胺酶诱导表达调控机制研究进展

β-内酰胺类抗生素是应用最广的一类抗菌药物。β-内酰胺酶能将β-内酰胺类抗生素水解,其诱导表达是革兰氏阴性菌对该类抗生素产生耐药性的最主要原因。文中重点综述了革兰氏阴性菌中β-内酰胺酶诱导表达的两种调控机制。在经典的ampR-ampC调控系统中,β-内酰胺酶的诱导表达与肽聚糖循环密切相关,并且LysR型转录因子AmpR发挥核心的调控作用。近年来发现β-内酰胺类抗生素能激活双组分系统,从而诱导β-内酰胺酶的表达。最后,讨论了革兰氏阴性菌中β-内酰胺类耐药今后的研究方向。     

TEM-1型β内酰胺酶的原核表达纯化及活性验证

目的:产β-内酰胺酶是大肠杆菌、肺炎克雷伯菌等对β内酰胺类抗生素耐药的主要机制之一,该酶能水解青霉素、头孢菌素、碳青酶烯类等多种抗生素,其中TEM型是发现最早且种类最多的β内酰胺酶。探讨TEM-1型β内酰胺酶原核表达载体的构建、酶的纯化及活性验证。方法:利用PCR技术,以大肠杆菌全基因组为模板钓取TEM-1基因,构建p ET22b(+)-TEM-1表达质粒,经测序鉴定后,转入大肠杆菌Transetta(DE3),IPTG诱导表达、亲和纯化,并通过抗生素水解实验验证其酶活性。结果:构建了可溶性表达TEM-1的工程菌,通过亲和纯化最终获得纯度达90%以上的TEM-1型β内酰胺酶,该酶可水解氨苄西林。结论:获得了对氨苄西林具有水解活性的TEM-1型β内酰胺酶,并对其进行了酶动力学参数检测,验证其抗生素水解特性,有利于对临床抗生素的合理应用做出指导。     

有机介质中脂肪酶催化外消旋苯甘氨酸甲酯的对映体选择性氨解反应

由水解酶催化的酯的对映体选择性水解和醇解反应 ,已在外消旋物质的拆分中得到广泛应用[1 ] 。近年来的一些研究表明 ,某些水解酶还可催化一些非天然酰基受体的转化 ,如过氧化氢、烷基胺、联胺和氨等。这些非天然酰基受体的转化反应在多肽的合成及手性化合物的拆分中显示出巨大的应用前景。其中 ,以氨为酰基受体的酶促氨解反应 ,是继酶促对映体选择性水解、酯化及转酯反应之后的另一制备光学纯化合物的新反应[2 ] 。目前国际上对这一新反应的研究尚属起步 ,国内未见有对该反应研究的报道。(Ｄ ,Ｌ) 苯甘氨酸是半合成 β 内酰胺类抗生素的重…     

琼胶酶研究进展

琼胶酶是一种多糖水解酶,根据其降解琼脂糖的作用方式不同,可以分为α-琼胶酶(EC 3.2.1.-)和β-琼胶酶(EC 3.2.1.81).本文结合自己的研究,从琼胶酶的生物学研究、酶的分类、晶体结构、催化机理以及酶的应用等几个方面综述了琼胶酶的研究进展.     

OKP-B-13型β-内酰胺酶的克隆与表达

目的构建OKP-B-13型β-内酰胺酶的表达载体。方法抽提菌株的质粒,应用PCR扩增OKP-B-13基因全长编码序列,扩增产物经Nde I、Xho I酶切后连接至pET-26b(+)表达载体,重组质粒经酶切及DNA测序确证后,转入大肠埃希菌BL21(DE3),IPTG诱导表达。超声破碎法提取表达蛋白产物,检测其活性,等电聚焦电泳检测蛋白的等电点(pI)。结果PCR扩增获得879 bp的产物,重组表达载体经Nde I、Xho I酶切及DNA测序后表明,目的基因已成功接入表达载体,重组菌的粗提物经头孢硝噻吩检测显示具有β-内酰胺酶活性,显示载体[pET-26b(+)/OKP-B-13]构建成功。目的等电点为7.1。结论β-内酰胺酶OKP-B-13在原核表达细胞中实验了基因重组表达,为进一步分析酶的特性提供条件。     

Purification and characterization of a novel (−) gamma-lactamase from<Emphasis Type="Italic">Microbacterium hydrocarbonoxydans</Emphasis>

A (?) gamma-lactamase fromMicrobacterium hydrocarbonoxydans was purified to homogeneity by chromatography methods. SDS-PAGE showed the molecular weight of the enzyme was about 31 kDa. The purified enzyme had a specific activity of 61.3±2.5 U mg^?1 for 2-azabicyclo [2.2.1] hept-5-en-3-one [(?) gamma-lactam]. The enantioselectivity factor (E) of the purified enzyme was 9.5±0.8 for unreacted (+) gamma-lactam. TheK _m andV _max value were 2.3±0.2 mM and 80.0±15.4 U mg^?1 respectively. The highest activity was found at 30 °C and pH 8.0. ESIMS mass spectrometry analysis results and N-terminal sequence indicated the (?) gamma-lactamase might be a new enzyme.     

The crystal structure of a (-) gamma-lactamase from an Aureobacterium species reveals a tetrahedral intermediate in the active site

The structure of the recombinant (-) gamma-lactamase from an Aureobacterium species has been solved at 1.73A resolution in the cubic space group F23 with unit cell parameters a=b=c=240.6A. The trimeric enzyme has an alpha/beta hydrolase fold and closely resembles the cofactor free haloperoxidases. The structure has been solved in complex with a covalently bound ligand originating from the host cell and also in the unligated form. The associated density in the former structure has been interpreted as the two-ring ligand (3aR,7aS)-3a,4,7,7a-tetrahydro-benzo [1,3] dioxol-2-one which forms a tetrahedral complex with OG of the catalytic Ser98. Soaks of these crystals with the industrial substrate gamma-lactam or its structural analogue, norcamphor, result in the displacement of the ligand from the enzyme active site, thereby allowing determination of the unligated structure. The presence of the ligand in the active site protects the enzyme from serine hydrolase inhibitors. Cyclic ethylene carbonate, the first ring of the ligand, was shown to be a substrate of the enzyme.     

Promiscuous (+)-γ-lactamase activity of an amidase from nitrile hydratase pathway for efficient synthesis of carbocyclic nucleosides intermediate

Based on bioinformatics analysis, the promiscuous (+)-γ-lactamase activity of an amidase was identified in Rhodococcus erythropolis PR4 and found to be involved in the nitrile hydratase pathway. The amidase is highly enantioselective and can be used in the kinetic resolution of the Vince lactam. The known structure provides a rare insight into the catalytic mechanism of (+)-γ-lactamase with absolute chiral selectivity. This lactamase was cloned, purified, biochemically characterized, and demonstrated to be an ideal catalyst for the preparation of carbocyclic nucleosides of pharmaceutical interest. The chiral selectivity of this enzyme was investigated by molecular docking and site-specific mutagenesis, which provides a foundation for further engineering of these versatile biocatalysts.     

Stereospecificγ-lactamase activity in aPseudomonas fluorescens species

Twenty five environmental isolates enriched for their ability to grow onN-acetylphenylalanine as sole carbon source were investigated for their hydrolytic action on (+)-lactam (2-azabicyclo[2.2.1]hept-5-en-3-one). Strain CMC 3060, a mucoidal Gram-negative rod identified as a strain ofPseudomonas fluorescens, produced high levels of (+)lactamase, and was subsequently found to produce two distinct intracellular enantiomer-selective, -lactamases, one for each isomer. The (+)lactamase was produced constitutively whereas the (-lactamase was produced only in the presence of the substrate. The (+)lactamase was stable when stored as a frozen cell paste but unstable as a protein solution, losing activity during purification and storage. This enzyme was highly selective for the (+)lactam and showed no activity against a wide range of similar compounds. By use of rapid purification techniques and the inclusion of protease inhibitors and protein stabilisers, the (+)lactamase was purified to homogeneity by FPLC and found to be a monomer of molecular weight 61000 Da.     

Inhibition of protein kinase C by a peptide conjugate homologous to a domain of the retroviral protein p15E

Retroviral infection is associated with immunosuppression, which has been shown to be due, in part, to the action of the envelope protein p15E. We studied a synthetic peptide (CKS-17) homologous to a highly conserved domain of the retroviral envelope protein p15E, which, when conjugated to BSA (CKS-17-BSA), can inhibit IL-1- and phorbol ester-mediated responses in cultured murine thymoma cells, and Ca2(+)- and phosphatidylserine-dependent protein kinase C (PKC) activity of cell homogenates. We characterized the mechanism of inhibition of PKC by the peptide. Using PKC purified from rat brain we found that CKS-17-BSA inhibited PKC-catalyzed Ca2(+)- and phosphatidylserine-dependent histone phosphorylation with an estimated ID50 of 4 microM. CKS-17-BSA did not inhibit the catalytic subunit of cAMP-dependent protein kinase. CKS-17-BSA also inhibited the Ca2(+)- and PS-independent activity of a catalytic fragment of PKC that was generated by limited trypsin treatment. However, CKS-17-BSA did not act as a competitive inhibitor of PKC with respect to ATP or phosphoacceptor substrate, despite the similarity between the CKS-17 sequence and substrates and pseudosubstrates of PKC. We conclude that this peptide homologue of a retroviral envelope protein has a novel mechanism of inhibition of PKC.     

Structure of the yeast Hst2 protein deacetylase in ternary complex with 2'-O-acetyl ADP ribose and histone peptide

Sir2 proteins are NAD(+)-dependant protein deactylases that have been implicated in playing roles in gene silencing, DNA repair, genome stability, longevity, metabolism, and cell physiology. To define the mechanism of Sir2 activity, we report the 1.5 A crystal structure of the yeast Hst2 (yHst2) Sir2 protein in ternary complex with 2'-O-acetyl ADP ribose and an acetylated histone H4 peptide. The structure captures both ligands meeting within an enclosed tunnel between the small and large domains of the catalytic protein core and permits the assignment of a detailed catalytic mechanism for the Sir2 proteins that is consistent with solution and enzymatic studies. Comparison of the ternary complex with the yHst2/NAD(+) complex, also reported here, and nascent yHst2 structure also reveals that NAD(+) binding accompanies intramolecular loop rearrangement for more stable NAD(+) and acetyl-lysine binding, and that acetyl-lysine peptide binding induces a trimer-monomer protein transition involving nonconserved Sir2 residues.     

Homoserine-derived cyclic sulfamidate as chiral educt for the diversity-oriented synthesis of lactam-bridged dipeptides

Introduction of structural constraint into peptides is an effective way for studying their conformation-activity relationships. Conformationally restrained dipeptidyl lactams, important building blocks for the synthesis of peptidomimetics, have now been synthesized from N-[9-(9-phenylfluorenyl)]-L-aspartic acid alpha-cumyl beta-methyl diester as an inexpensive chiral educt. After selective reduction of the beta-methyl ester with diisobutylaluminum hydride (DIBAL-H), homoserine was treated with thionyl chloride, imidazole, and triethylamine to give sulfamidites. Diastereoisomers were separated by chromatography and oxidation of the major sulfamidite (2R,4S)- with catalytic ruthenium trichloride afforded sulfamidate. A series of gamma-lactam-bridged dipeptides was then obtained by ring opening of sulfamidate cumyl ester with a series of amino esters, selective cumyl ester removal, and lactam formation. The resulting dipeptidyl lactams possessed aliphatic, aromatic, amino, thioether, and carboxylate side chains. A gamma-lactam analog of Pro-Leu-Gly-NH2 (PLG), was synthesized to illustrate the potential for using this approach in the synthesis of biologically active peptide mimics.     

Novel screening methods--the key to cloning commercially successful biocatalysts

Providing sufficient biocatalyst to support the demands of multi tonne product supply can be problematical. Here we describe how screening for and cloning a gamma-lactamase overcame biocatalyst supply issues, and greatly improved the actual biocatalytic process. The isolation of an expressing gamma-lactamase clone from a gene library necessitated a combination of classical molecular biology techniques together with innovative screening methods to identify a functional clone. Once isolated the enzyme was characterised with regard to its process performance and proved to be active at 500 g L(-1) substrate. Further development of the recombinant fermentation and downstream processing has resulted in the ability to produce sufficient biocatalyst from one 5001 fermentation to resolve 5 metric tonnes of (+/-)-lactam, whilst simplifying the process chemistry greatly.     

Identification of amino acid residues essential for onion lachrymatory factor synthase activity

Lachrymatory factor synthase (LFS), an enzyme essential for the synthesis of the onion lachrymatory factor (propanethial S-oxide), was identified in 2002. This was the first reported enzyme involved in the production of thioaldehyde S-oxides via an intra-molecular H(+) substitution reaction, and we therefore attempted to identify the catalytic amino acid residues of LFS as the first step in elucidating the unique catalytic reaction mechanism of this enzyme. A comparison of the LFS cDNA sequences among lachrymatory Allium plants, a deletion analysis and site-directed mutagenesis enabled us to identify two amino acids (Arg71 and Glu88) that were indispensable to the LFS activity. Homology modeling was performed for LFS/23-169 on the basis of the template structure of a pyrabactin resistance 1-like protein (PYL) which had been selected from a BLASTP search on SWISS-MODEL against LFS/23-169. We identified in the modeled structure of LFS a pocket corresponding to the ligand-binding site in PYL, and Arg71 and Glu88 were located in this pocket.