Effect of mutations on acetohydroxyacid synthase(AHAS)function in Cyperus difformis L.

Cyperus difformis L.is a troublesome weed in paddy fields and has attracted attention due to its resistance to acetohydroxyacid synthase(AHAS)inhibitors.It was found that the amino acid mutation in AHAS was the primary cause for the resistance of Cyperus difformis.However,the effect of different mutations on AHAS function is not clear in Cyperus difformis.To confirm the effect of mutations on AHAS function,six biotypes were collected,including Pro197Arg,Pro197Ser,Pro197Leu,Asp376Glu,Trp574Leu and wild type,from Hunan,Anhui,Jiangxi and Jiangsu provinces,China and the function of AHAS was characterized.The AHAS in vitro inhibition assay results indicated that the mutations decreased the sensitivity of AHAS to pyrazosulfuron-ethyl,in which the I_(50)(the half maximal inhibitory concentration)of wild type AHAS was 0.04μmol L^(-1)and Asp376Glu,Pro197Leu,Pro197Arg,Pro197Ser and Trp574Leu mutations were 3.98,11.50,40.38,38.19 and 311.43μmol L^(-1),respectively.In the determination of enzyme kinetics parameters,the Km and the maximum reaction velocity(Vmax)of the wild type were 5.18 mmol L^(-1)and 0.12 nmol mg^(-1)min^(-1),respectively,and the Km values of AHAS with Asp376Glu,Trp574Leu,Pro197Leu and Pro197Ser mutations were 0.38-0.93 times of the wild type.The Km value of the Pro197Arg mutation was 1.14times of the wild type,and the Vmax values of the five mutations were 1.17-3.33-fold compared to the wild type.It was found that the mutations increased the affinity of AHAS to the substrate,except for the Pro197Arg mutation.At a concentration of 0.0032-100 mmol L^(-1)branched-chain amino acids(BCAAs),the sensitivity of the other four mutant AHAS biotypes to feedback inhibition decreased,except for the Pro197Arg mutation.This study elucidated the effect of different mutations on AHAS function in Cyperus difformis and provided ideas for further study of resistance development.

Development and molecular analysis of a novel acetohydroxyacid synthase rapeseed mutant with high resistance to sulfonylurea herbicides

With the increasing promotion of simplified rapeseed cultivation in recent years,the development of cultivars with high resistance to herbicides is urgently needed.We previously developed M342,which shows sulfonylurea herbicide resistance,by targeting acetohydroxyacid synthase(AHAS),a key enzyme in branched-chain amino acid synthesis.In the present study,we used a progeny line derived from M342 for an additional round of ethyl methane sulfonate mutagenesis,yielding the novel mutant DS3,which harbored two mutations in AHAS genes and showed high sulfonylurea resistance.One mutation was the substitution Trp574 Leu,as in M342,according to Arabidopsis protein sequencing.The other site was a newly recognized substitution,Pro197 Leu.A KASP marker targeting Pro197 Leu was developed and reliably predicted the response to sulfonylurea herbicides in the F2 population.The combination of Trp574 Leu and Pro197 Leu in DS3 produced a synergistic effect that greatly increased herbicide resistance.Analysis of the protein structures of AHAS1 and AHAS3 in wild-type and single-gene mutant plants revealed three-dimensional protein conformational changes that could account for differences in herbicide resistance characteristics including toxicity tolerance,AHAS enzyme activity,and AHAS gene expression.

Synthesis and Characterization of Novel Acetohydroxyacid Synthase Inhibitors

A novel kind of acetohydroxyacid synthase（AHAS） inhibitors, arylsulfonylaminocarbonyl-2-thiohydantoins, was synthesized based on biorational design. The structures of these compounds were confirmed by IR, MS, NMR, and elemental analysis. The results of the preliminary activity tests indicate that most of the arylsulfonylamidecarbonyl-5- methyl-2-thiohydantoins have a higher biological activity than those without 5-methyl substituent.

Insight into herbicide resistance of W574L mutant Arabidopsis thaliana acetohydroxyacid synthase:molecular dynamics simulations and binding free energy calculations

Acetohydroxyacid synthase(AHAS) is the target enzyme of several classes of herbicides,such as sulfonylureas and imidazolinones.Now many mutant AHASs with herbicide resistance have emerged along with extensive use of herbicides,therefore it is imperative to understand the detailed interaction mechanism and resistance mechanism so as to develop new potent inhibitors for wild-type or resistant AHAS.With the aid of available crystal structures of the Arabidopsis thaliana(At) AHAS-inhibitor complex,molecular dynamics(MD) simulations were used to investigate the interaction and resistance mechanism directly and dynamically at the atomic level.Nanosecond-level MD simulations were performed on six systems consisting of wild-type or W574L mutant AtAHAS in the complex with three sulfonylurea inhibitors,separately,and binding free energy was calculated for each system using the MM-GBSA method.Comprehensive analyses from structural and energetic aspects confirmed the importance of residue W574,and also indicated that W574L mutation might alert the structural charactersistic of the substrate access channel and decrease the binding affinity of inhibitors,which cooperatively weaken the effective channel-blocked effect and finally result in weaker inhibitory effect of inhibitor and corresponding herbicide resistance of W574L mutant.To our knowledge,it is the first report about MD simulations study on the AHAS-related system,which will pave the way to study the interactions between herbicides and wild-type or mutant AHAS dynamically,and decipher the resistance mechanism at the atomic level for better designing new potent anti-resistance herbicides.

Homologous and heterologous interactions between catalytic and regulatory subunits of Escherichia coli acetohydroxyacid synthaseⅠand Ⅲ

Homologous and heterologous interactions between acetohydroxyacid synthase (AHAS) I and Ⅲ from E. coli have been studied by surface plasmon resonance (SPR). The catalytic and regulatory subunits association for AHAS I (KD = 1.13 × 10-7 M) was stronger than that for AHAS Ⅲ (KD = 5.29 × 10-7 M). A strong heterologous association between regulatory and catalytic subunits and heterologous activation of catalytic subunits were observed. SPR results combined with enzyme kinetics indicate that the reconstituted heterologous enzymes had similar kinetic properties as homologous enzymes, implying that the regulatory subunit of AHAS I could be replaced by the regulatory subunit of AHAS Ⅲ and vice versa. This work may be useful to further understandings of the mechanism of regulation of AHAS.

Experimental and computational correlation and prediction on herbicide resistance for acetohydroxyacid synthase mutants to Bispyribac

Bispyribac is a widely used herbicide that targets the acetohydroxyacid synthase （AHAS） enzyme. Mutations in AHAS have caused serious herbicide resistance that threatened the continued use of the herbicide. So far, a unified model to decipher herb- icide resistance in molecular level with good prediction is still lacking. In this paper, we have established a new QSAR method to construct a prediction model for AHAS mutation resistance to herbicide Bispyribac. A series of AHAS mutants concerned with the herbicide resistance were constructed, and the inhibitory properties of Bispyribac against these mutants were meas- ured. The 3D-QSAR method has been transformed to process the AHAS mutants and proposed as mutation-dependent biom- acromolecular QSAR （MB-QSAR）. The excellent correlation between experimental and computational data gave the MB-QSAR/CoMFA model （q2 = 0.615, P = 0.921, F2pred = 0.598） and the MB-QSAR/CoMSIA model （q2 = 0.446, r2 = 0.929, r2pred = 0.612）, which showed good prediction for the inhibition properties of Bispyribac against AHAS mutants. Such MB-QSAR models, containing the three-dimensional molecular interaction diagram, not only disclose to us for the first time the detailed three-dimensional information about the structure-resistance relationships, but may also provide further guidance to resistance mutation evolution. Also, the molecular interaction diagram derived from MB-QSAR models may aid the resistance-evading herbicide design.

Molecular Drug Resistance Prediction for Acetohydroxyacid Synthase Mutants Against Chlorsulfuron Using MB-QSAR

Chlorsulfuron is the first commercialized sulfonylurea herbicide, which targets acetohydroxyacid synthase （AHAS）. Mutations in AHAS have caused serious herbicide resistance to chlorsulfuron. Quantitative description of the herbicide resistance in molecular level will benefit the understanding of the resistance mechanism and aid the design of resistance-evading herbicide. We have recently established a MB-QSAR （Mutation-dependent Biomac- romolecular Quantitative Structure-Activity Relationship） method to conduct the 3D-QSAR study in biomacro- molecules. Herein, based on the herbicide resistance data measured for a series of AHAS mutants against chlorsul- furon, we constructed MB-QSAR models to quantitatively predict the herbicide resistance and interpret the struc- ture resistance relationships for AHAS mutants against chlorsulfuron. Quite well correlations between the experi- mental and the predicted pKi values were achieved for MB-QSAR/CoMFA （q^2=0.705, r^2=0.918, r^2pred=0.635） and MB-QSAR/CoMSIA （q^2=0.558, r^2=0.940, r^2pred=0.527） models, and interpretation of the MB-QSAR models gave chemical intuitive information to guide the resistance-evading herbicide design.

Study on structure-activity relationship of mutation-dependent herbicide resistance acetohydroxyacid synthase through 3D-QSAR and mutation

Seventy-four sulfonylureas were synthesized and tested for their inhibitory activity against the whole enzyme of E. coli acetohydroxyacid synthase (AHAS, EC 2.2.1.6) isoenzyme II, and 3D-QSAR analyses were performed based on these inhibitory activities. The binding conformation of chlorimuron-ethyl, a commercial herbicide of AHAS, in the crystal structure of AHAS complex was extracted and used as template to build the initial three-dimensional structure of other sulfonylureas, and then all structures were fully geometry optimized. After systematic optimization of the alignment rule, molecular orienta- tion, grid space and attenuation factor, two satisfactory models with excellent performances (CoMFA: q2 = 0.735, r2 = 0.954, n = 7, r 2 pred = 0.832; CoMSIA: q2 = 0.721, r2 = 0.913, n = 8, r 2pred = 0.844) were estab- lished. By mapping the 3D contour maps of CoMFA and CoMSIA models into the possible inhibitory active site in the crystal structure of catalytic subunit of yeast AHAS, a plausible binding model for AHAS, with best fit QSAR in the literature so far, was proposed. Moreover, the results of 3D-QSAR were further utilized to interpret resistance of site-directed mutants. A relative activity index (RAI) for AHAS enzyme mutant was defined for the first time to relate the 3D-QSAR and resistance of mutants. This study, for the first time, demonstrated that combination of 3D-QSAR and enzyme mutation can be used to decipher the molecular basis of ligand-receptor interaction mechanism. This study refined our understanding of the ligand-receptor interaction and resistance mechanism in AHAS-sulfonylurea system, and provided basis for designing new potent herbicides to combat the herbicide resistance.

除草剂靶酶—AHAS酶及基因突变体与除草剂设计(I)·野生型和突变型E.coliAHAS II酶动力学性质的系统研究

针对除草剂敏感型乙酰羟基酸合成酶E.coliAHAS II的抗性域,引入W 464A、W 464F、W 464L、W 464Y点突变。采用Megaprimer PCR定点突变,测序鉴定,构建了4个E.coliAHASIIW 464位点的突变体。通过对E.coliAHAS II野生型及突变体动力学性质的测定,发现它们对于底物—丙酮酸及3种辅助因子(FAD、ThDP、Mg2+)有着不同的特征常数。这些部分抗性酶系的建立以及对动力学性质的系统研究,为探讨AHAS酶对农药分子抗性的作用机制、设计合成新除草剂及其筛选体系提供了基础。

除草剂靶酶—AHAS酶及基因突变体与除草剂设计(Ⅱ).AHAS及W464突变酶与除草活性分子的相互作用

乙酰羟基酸合成酶(AHAS)是磺酰脲类、咪唑啉酮类、三唑嘧啶磺酰胺类及水杨酸类除草剂的作用靶标,大田使用中杂草对这几类除草剂产生抗性的主要因素是AHAS酶的突变.利用大肠杆菌AHASⅡ中464位的色氨酸突变体(W464A、W464F、W464L、W464Y),研究了野生型和突变酶对商品化除草剂(氯嘧磺隆、氯磺隆、咪唑乙烟酸、咪唑喹啉酸)以及烷硫基磺酰脲的敏感性.野生型E.coli AHASⅡ对这些化合物的抑制作用较为敏感,而突变酶对其呈现出不同程度的抗性,使商品化除草剂的抑制常数增加了10～1.0×104倍不等,烷硫基磺酰脲的抑制常数增加幅度较小.烷硫基磺酰脲1a对W464L突变酶的高抑制活性,暗示着发展针对靶酶抗性的除草剂的可能性.

拟南芥乙酰羟基酸合成酶与磺酰脲的相互作用以及CoMFA研究

在分子水平上较为详尽地研究了85个磺酰脲类化合物与植物源野生型拟南芥AHAS酶的离体相互作用,测定了这些化合物对AHAS酶的抑制常数Kiapp.采用比较分子力场方法(CoMFA)对这些化合物与AHAS酶的相互作用进行了三维构效关系研究,用此模型预测了检验组10个化合物的pKiapp值,模型的预测结果与测试结果一致.

抗甲磺隆假单胞菌的分离及其乙酰乳酸合酶的大小亚基ilvIH基因的克隆和表达

乙酰乳酸合酶(也称乙酰羟酸合酶acetohydroxyacid synthase,AHAS)是植物、真菌和细菌细胞内支链氨基酸Val、Leu、Ile生物合成过程中关键酶,是乙酰乳酸合酶抑制剂类除草剂如磺酰脲类、咪唑啉酮类、嘧啶水杨酸和磺酰氨类的作用靶标。【目的】获得抗甲磺隆的乙酰乳酸合酶基因,构建其表达载体,并分析基因中的位点突变与乙酰乳酸合酶对磺酰脲类除草剂抗性产生原因。【方法】从长期使用甲磺隆的土壤中分离到1株抗甲磺隆的菌株Lm10,利用PCR技术从Lm10总DNA中克隆到乙酰乳酸合酶的大小亚基基因ilvIH,对ilvIH氨基酸序列进行比对分析。分别将ilvI和ilvH分别连接到表达载体pET29a(+)多克隆位点,转化大肠杆菌(Escherichia coli)获得转化子BL21(pET-I)和BL21(pET-H),并诱导表达。【结果】菌株Lm10鉴定为假单孢菌(Pseudomonas sp.),对甲磺隆的最高耐受浓度达到14000μmol//L,且对各种乙酰乳酸合酶抑制剂类除草剂具有交叉抗性。Lm10与甲磺隆敏感菌株KT2440的小亚基氨基酸序列完全相同,而大亚基有6个氨基酸位点发生变异。转化子在IPTG诱导下,乙酰乳酸合酶的大小亚基的蛋白成功表达,粗酶液酶活试验结果表明Lm10的ilvI基因表达的乙酰乳酸合酶大亚基对甲磺隆有很强的抗性。【结论】发现菌株Lm10的乙酰乳酸合酶大亚基对甲磺隆有很强的抗性,抗甲磺隆菌株Lm10与敏感菌株KT2440的ilvI有6个氨基酸位点差异,这些位点突变可能是乙酰乳酸合酶对甲磺隆抗性产生的原因。

低双乙酰啤酒酵母工程菌的构建

利用PCR技术以啤酒酵母QY的染色体为模板扩增出含有乙酰羟酸合成酶 (AHAS)基因ILV2的片段 ,将ILV2基因的内部EcoRI片段连接到整合载体YIp5上 ,并在该载体的BamHI -SalI位点插入铜抗性基因CUP1-MT1,构建了YIpCE质粒 ,将其转化啤酒酵母QY ,所得到的转化子AHAS酶的活力比受体菌QY降低75 %左右 ,在发酵测试中 ,转化了产生双乙酰的量比原始菌株降低 30 %。

N-(4'-芳环取代嘧啶基-2'-基)-2-乙氧羰基苯磺酰脲衍生物的合成及抑菌活性

设计合成了14个4位芳环取代的嘧啶磺酰脲衍生物,其结构均通过1H NMR和高分辨质谱表征确定,并进行了体外抑菌活性测试.初步测试结果表明,在浓度为50 mg/L时,大部分目标化合物对黄瓜灰霉病、油菜菌核病和水稻纹枯病表现出一定的抑菌效果,其中化合物7g,7h和7i表现出较高的抑菌活性;但大部分目标化合物对黄瓜枯萎病、黄瓜褐斑病及苹果轮纹病的抑菌活性与对照药百菌清尚有差距.

一种安全高效大豆转化筛选体系的建立

以灭草烟作为筛选剂,利用基因枪法建立一种安全高效的大豆遗传转化体系。比较不同筛选剂对大豆胚尖外植体丛生芽诱导数目的影响。与卡那霉素、潮霉素和草胺膦等传统筛选剂相比,以灭草烟作为筛选剂可使丛生芽的数目增加1倍以上。克隆了拟南芥突变体csr1-2中突变的乙酰羟基酸合成酶基因(ahas),以其作为筛选标记基因,构建可利用灭草烟作为筛选剂的植物表达载体。利用基因枪法将该载体转化大豆,获得6棵灭草烟抗性植株,分子检测证明外源ahas基因整合到5棵转基因大豆植株的基因组中。

油菜乙酰羟基酸合酶基因BnAHAS1的克隆及其重组蛋白质的原核表达

利用RT-PCR技术从甘蓝型油菜宁油16号(Brassica napus L.)中克隆到乙酰羟基酸合酶基因BnAHAS1的cDNA序列,该序列含有1个1 968 bp的开放阅读框,编码蛋白质655个氨基酸,分子量约为7.1×104,预测等电点为6.16。将该基因克隆到原核表达载体pCold II中,经酶切和测序鉴定后,将正确的重组质粒pCold IIBnAHAS1导入大肠杆菌BL21(DE3)。在15℃下以终浓度为1 mmol/L的IPTG诱导12 h后,获得预期大小的重组蛋白质His-BnAHAS1,并用Western blot确定此重组蛋白质为目的蛋白质。

新型芳磺酰基色氨酸酯以及芳磺酰基谷氨酸二酯类化合物的合成与生物活性研究

在乙酰羟酸合成酶(AHAS)与磺酰脲类化合物复合物晶体结构的基础上,利用分子对接法进行MDL/ACD三维数据库虚拟筛选,得到了部分结合能较低的小分子化合物结构.对其中的芳磺酰基色氨酸酯以及芳磺酰基谷氨酸二酯类化合物进行了合成,共合成22个具有潜在活性的新衍生化合物,其结构通过核磁、质谱、红外及元素分析验证,并对所有新化合物进行了体内、体外活性测试.初步的体外生物活性测试结果表明,两类化合物对AHAS具有较低的抑制性;体内生物活性测试结果表明,化合物4d,4g和4k具有一定的除草活性,在100μg/mL的浓度下,它们对油菜根长的抑制率分别为70.8%,52.4%和50.2%.

新型2-乙内酰硫脲衍生物的合成与表征

通过异氰酸酯法合成一系列新型2-乙内酰硫脲衍生物,应用1H NMR、13C NMR、IR测试技术对分子的结构进行了表征;初步测定了化合物的除草活性;对构效关系进行了分析。结果表明,在乙内酰硫脲5位上含有甲基取代基的化合物的除草活性要高于5位上没有取代基的化合物。最大的芽抑制率为56.5%,最大的根抑制率为53.8%。2-乙内酰硫脲衍生物可以作为一类新的农药先导化合物。

乙酰乳酸合成酶及其抑制剂研究新进展

乙酰乳酸合成酶(AHAS)是支链氨基酸生物合成途径中的一个关键酶,是绿色除草剂的重要作用靶标。由于此生物合成过程只存在于植物和微生物体内,因此该类抑制剂对哺乳动物具有生物安全性。近年来,随着AHAS三维结构的阐明,人们不仅深入了解了已有抑制剂的作用机制,并且依此设计开发了一些新型的抑制剂,拓展了其在抑菌活性方面的生物学功能。文章对近年来AHAS及其抑制剂的最新研究进展进行了综述,重点就AHAS的酶学特征、结构特征及结合方式,以AHAS为靶标的新颖除草活性化合物的设计开发以及AHAS抑制剂的抗菌生物活性研究进展等问题详细进行了总结,以期为设计开发靶向AHAS的新型除草剂或抗菌药物提供参考。

Synthesis and Characterization of Novel-4-Methyl-3-isoxazolidinone Derivatives

A novel type of aeetohydrexyacid synthase inhibitors, 4-methyl-3-isoxazolidinone derivatives of sulfonylurea, was designed and synthesized. The structures of these compounds were confirmed by using MS, NMR, and elemental analysis. The results of preliminary active tests indicate that the compounds show a herbicidal activity.