Metabolite Profiling Reveals a Role for Atypical Cinnamyl Alcohol Dehydrogenase CAD1 in the Synthesis of Coniferyl Alcohol in Tobacco Xylem

In angiosperms, lignin is built from two main monomers, coniferyl and sinapyl alcohol, which are incorporated respectively as G and S units in the polymer. The last step of their synthesis has so far been considered to be performed by a family of dimeric cinnamyl alcohol dehydrogenases (CAD2). However, previous studies on Eucalyptus gunnii xylem showed the presence of an additional, structurally unrelated, monomeric CAD form named CAD1. This form reduces coniferaldehyde to coniferyl alcohol, but is inactive on sinapaldehyde. In this paper, we report the functional characterization of CAD1 in tobacco (Nicotiana tabacum L.). Transgenic tobacco plants with reduced CAD1 expression were obtained through an RNAi strategy. These plants displayed normal growth and development, and detailed biochemical studies were needed to reveal a role for CAD1. Lignin analyses showed that CAD1 down-regulation does not affect Klason lignin content, and has a moderate impact on G unit content of the non-condensed lignin fraction. However, comparative metabolic profiling of the methanol-soluble phenolic fraction from basal xylem revealed significant differences between CAD1 down-regulated and wild-type plants. Eight compounds were less abundant in CAD1 down-regulated lines, five of which were identified as dimers or trimers of monolignols, each containing at least one moiety derived from coniferyl alcohol. In addition, 3-trans-caffeoyl quinic acid accumulated in the transgenic plants. Together, our results support a significant contribution of CAD1 to the synthesis of coniferyl alcohol in planta, along with the previously characterized CAD2 enzymes. Sequences of NtCAD1-1 and NtCAD1-7 were deposited in GenBank under accession numbers AY911854 and AY911855, respectively.     

Characterization of two isozymes of coniferyl alcohol dehydrogenase from Streptomyces sp. NL15-2K

We purified two isozymes of coniferyl alcohol dehydrogenase (CADH I and II) to homogeneity from cell-free extracts of Streptomyces sp. NL15-2K. The apparent molecular masses of CADH I and II were determined to be 143 kDa and 151 kDa respectively by gel filtration, whereas their subunit molecular masses were determined to be 35,782.2 Da and 37,597.7 Da respectively by matrix-assisted laser-desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS). Thus, it is probable that both isozymes are tetramers. The optimum pH and temperature for coniferyl alcohol dehydrogenase activity were pH 9.5 and 45 °C for CADH I and pH 8.5 and 40 °C for CADH II. CADH I oxidized various aromatic alcohols and allyl alcohol, and was most efficient on cinnamyl alcohol, whereas CADH II exhibited high substrate specificity for coniferyl alcohol, and showed no activity as to the other alcohols, except for cinnamyl alcohol and 3-(4-hydroxy-3-methoxyphenyl)-1-propanol. In the presence of NADH, CADH I and II reduced cinnamaldehyde and coniferyl aldehyde respectively to the corresponding alcohols.     

Substrate Specificity of a Novel Alcohol Resistant Metalloproteinase,Vimelysin, from Vibrio sp. T1800

Vimelysin is a novel alcohol resistant metalloproteinase from Vibrio sp. T1800. The substrate specificity of vimelysin was studied by using natural and furylacryloyl dipeptide substrates. Vimelysin cleaved mainly Pro⁷-Phe⁸ bond and slightly Tyr⁴-Ile⁵ bond in human angiotensin I. Vimelysin also cleaved mainly Phe²⁴-Phe²⁵ and Tyr¹⁶-Leu¹⁷ bonds, and slightly His⁵-Leu⁶, His¹⁰-Leu¹¹, Ala¹⁴-Leu¹⁵, and Gly²³-Phe²⁴ bonds in oxidized insulin B-chain. The substrate specificity of vimelysin, by using furylacryloyl (Fua) dipeptides were also studied. The ratio of k_cat/K_m for Fua-Gly-Phe-NH₂/Fua-Gly-Leu-NH₂, Fua-Phe-Leu-NH₂/Fua-Gly-Leu-NH₂, and Fua-Phe-Phe-NH₂/Fua-Gly-Leu-NH₂ were 15.9, 27.8, and 59.0, respectively. These results indicate that vimelysin easily recognizes phenylalanine in P1′ positions, which is different from thermolysin.     

Cloning and Characterization of the Gene Encoding Pyrroloquinoline Quinone-dependent Poly (vinyl alcohol) Dehydrogenase of Pseudomonas sp. Strain VM15C

A gene library of poly (vinyl alcohol) (PVA)-degrading Pseudomonas sp. strain VM15C was constructed in Escherichia coli with the vector pUC18. Screening of this library with a chromogenic PVA dehydrogenase assay resulted in the isolation of a clone that carries the gene (pdh) for the PVA dehydrogenase, and the entire nucleotide sequence of its structural gene was determined. The gene encodes a protein of 639 amino acid residues (68,045 Da) and in the deduced amino acid sequence, some putative functional sites, a signal sequence, a heme c-binding site, and a PQQ-binding site, were detected. The amino acid sequence showed low similarity to other types of quinoprotein dehydrogenases. PVA dehydrogenase expressed in E. coli clones required PQQ. Ca²⁺, and Mg²⁺ stimulated the activity. PVA-dependent heme c reduction occurred with exogenous PQQ in cell extracts of the E. coli clone. The PVA dehydrogenase in the E. coli clone was localized in the cytoplasm.     

Classification of novel soil streptomycetes as Streptomyces aureus sp. nov., Streptomyces laceyi sp. nov. and Streptomyces sanglieri sp. nov

The taxonomic positions of soil isolates known as Streptomyces groups A, B and C were clarified. Comparative 16S rDNA sequence studies indicated that representatives of all three taxa formed distinct phyletic lines within the Streptomyces tree though the group A strains were shown to be related to Streptomyces griseus and associated validly described species. The taxonomic integrity of all three groups was highlighted by DNA:DNA relatedness and ribotype data though the group A strains encompassed a higher degree of genetic variation than the group B and C strains. In light of these and earlier phenotypic data it is proposed that Streptomyces groups A, B and C be given species status as Streptomyces sanglieri sp. nov., Streptomyces aureus sp. nov. and Streptomyces laceyi sp. nov., respectively. This revised version was published online in June 2006 with corrections to the Cover Date.     

植物肉桂醇脱氢酶及其基因研究进展

肉桂醇脱氢酶(cinnamyl alcohol dehydrogenase,CAD)作为植物次生代谢特别是木质素合成的关键酶,与植物生长发育和抵御病原菌入侵关系密切,研究CAD基因表达调控及其与组织木质化的关系具有重要的植物生理学意义.该文综述了植物CAD的蛋白特征、酶学性质、基因分布和分类、基因结构和表达调控以及CAD表达与木质素合成的关系,为研究CAD在植物生长发育和抗病中的作用提供理论指导.     

Improved Paper Pulp from Plants with Suppressed Cinnamoyl-CoA Reductase or Cinnamyl Alcohol Dehydrogenase

Transgenic plants severely suppressed in the activity of cinnamoyl-CoA reductase were produced by introduction of a partial sense CCR transgene into tobacco. Five transgenic lines with CCR activities ranging from 2 to 48% of wild-type values were selected for further study. Some lines showed a range of aberrant phenotypes including reduced growth, and all had changes to lignin structure making the polymer more susceptible to alkali extraction. The most severely CCR-suppressed line also had significantly decreased lignin content and an increased proportion of free phenolic groups in non-condensed lignin. These changes are likely to make the lignin easier to extract during chemical pulping. Direct Kraft pulping trials confirmed this. More lignin could be removed from the transgenic wood than from wild-type wood at the same alkali charge. A similar improvement in pulping efficiency was recently shown for poplar trees expressing an antisense cinnamyl alcohol dehydrogenase gene. Pulping experiments performed here on CAD-antisense tobacco plants produced near-identical results – the modified lignin was more easily removed during pulping without any adverse effects on the quality of the pulp or paper produced. These results suggest that pulping experiments performed in tobacco can be predictive of the results that will be obtained in trees such as poplar, extending the utility of the tobacco model. On the basis of our results on CCR manipulation in tobacco, we predict that CCR-suppressed trees may show pulping benefits. However, it is likely that CCR-suppression will not be the optimal target for genetic manipulation of pulping character due to the potential associated growth defects.     

链霉菌Strz-6木聚糖酶的纯化和固定化研究

链霉菌胞外木聚糖酶经过盐析、离子交换和分子筛层析纯化,粗酶液被纯化了32.5倍,比活力达498u/mg,活力回收46.6%。纯化后的酶固定在戊二醛交联的壳聚糖上,酶活回收率为42.8%。固定化酶的最适pH为6.0,最适温度为60℃,且固定化酶在65~75℃活力都较高。该酶的耐热性比较强,固定化酶热稳定性优于原酶;以木聚糖为底物,固定化酶的表观米氏常数为0.93×10-2g/L。     

变铅青链霉菌异柠檬酸脱氢酶的异源表达及序列分析

通过同源性引物成功扩增和克隆了变铅青链霉菌(Streptomyces lividans)TK54的异柠檬酸脱氢酶(isocitrate dehydrogenase, IDH) (简称SlIDH)基因icd (GenBank登录号为EU661252).icd的起始密码子为GTG,GC含量为69.55 %,显示了链霉菌基因的高GC含量特征,实现了SlIDH在E.coli中的异源高效表达.0.5 mmol/L的IPTG为最佳诱导条件.SlIDH的分子量约为80 kD.在Mn~(2+)或Mg~(2+)条件下,SlIDH以NADP~+为辅酶时的活性分别为7.94 U/mg及4.00 U/mg,以NAD~+为辅酶时的活性分别为0.58 U/mg及0.27 U/mg,SlIDH更偏爱以NADP~+为辅酶.与不同种属单体IDH的氨基酸序列比对显示,SlIDH与单体IDH的序列一致性均在60 %以上.因此本工作首次以实验性证据初步鉴定了SlIDH为NADP-依赖型单体IDH.本工作为进一步探索单体IDH的结构与功能以及单体IDH与同源二聚体IDH的进化关系奠定了基础.     

Secondary metabolites from endophytic Streptomyces sp. Lz531

From the branch tissue of Maytenus hookeri, the endophytic strain Lz531 was isolated, and determined to belong to Streptomyces, according to its 16S rRNA sequence. From the extracts of the fermentation broth of Streptomyces sp. Lz531, two new and four known compounds were isolated. The two new compounds were identified as cyclo(L-Pro-L-Val-L-Val) (1) and 13-methyl-N-(2-phenylethyl)tetradecanamide (2).     

Ansaetherone,a New Radical Scavenger from Streptomyces sp.

We identified a new radical scavenger, ansaetherone (C₂₆H₃₃NO₇), from a culture of the Streptomyces sp. USF-4727 strain. In our previous study, it was shown that this strain produced four lipoxygenase inhibitors, tetrapetalones A, B, C and D. The chemical structure of ansaetherone was elucidated by the spectroscopic method, indicating that this compound was constructed with an aglycon and a sugar moiety. This chemical structure suggested that ansaetherone was related to the tetrapetalones. This finding provided information regarding tetrapetalone biosynthesis. Ansaetherone showed radical scavenging activity with an ED₅₀ value of 300 μM in our assay.     

链霉菌Strz-2胞外木聚糖酶的纯化和固定化研究

为探讨木聚糖酶被固定化后的酶活力变化 ,采用盐析、离子交换和分子筛层析方法对链霉菌胞外木聚糖酶进行了纯化 ,并采用DNS方法对固定化酶的性质进行了研究。结果如下 :粗酶液被纯化了 30 .5倍 ,比活力达 4 5 7.5 ,活力回收 4 2 .6 %。纯化后的酶固定在戊二醛交联的壳聚糖上 ,残活力为 4 1.8%。固定化酶的最适pH为 6 .0 ,最适温度为 5 5℃ ,且固定化酶在 6 5 -75℃活力都较高。该酶的耐热性比较强 ,固定化酶热稳定性优于原酶 ;以木聚糖为底物 ,固定化酶的表观米氏常数为 0 .83× 10 -2g/L。因此 ,固定化的木聚糖酶优于原酶     

香蕉肉桂醇脱氢酶基因的克隆及表达分析

肉桂醇脱氢酶(CAD)在木质素合成过程中起关键作用。通过RACE(rapid-amplification of cDNA ends)方法从香蕉根系cDNA均一化全长文库中获得一个肉桂醇脱氢酶基因,命名为MaCAD1(GenBank登录号为KF582533)。MaCAD1是香蕉MYB基因编码框全长cDNA,包含一个1 077bp的最大开放阅读框(ORF),编码358个氨基酸。蛋白质序列同源比对发现,其含有完整的醇脱氧酶的典型保守结构域,属于典型的CAD蛋白。系统进化树比对分析表明,MaCAD1与水稻OsCAD6(CAD39907)的亲缘关系较近。组织特异性研究表明MaCAD1基因组成型表达于香蕉各个组织。在耐病和感病品种中,MaCAD1均上调表达,但在耐病品种中MaCAD1在所有时间点相对于对照增加的倍数均高于感病品种,表明MaCAD1基因在香蕉的抗病性中起着重要作用,MaCAD1可以作为一个新的响应枯萎病侵染的标记基因。     

Cloning and identification of saprolmycin biosynthetic gene cluster from Streptomyces sp. TK08046

Saprolmycins A–E are anti-Saprolegnia parasitica antibiotics. To identify the gene cluster for saprolmycin biosynthesis in Streptomyces sp. TK08046, polymerase chain reaction using aromatase and cyclase gene-specific primers was performed; the spr gene cluster, which codes for angucycline biosynthesis, was obtained from the strain. The cluster consists of 36 open reading frames, including minimal polyketide synthase, ketoreductase, aromatase, cyclase, oxygenase, and deoxy sugar biosynthetic genes, as defined by homology to the corresponding genes of the urdamycin, Sch-47554, and grincamycin biosynthetic gene clusters in Streptomyces fradiae, Streptomyces sp. SCC-2136, and Streptomyces lusitanus, respectively. To establish the function of the gene cluster, an expression cosmid vector containing all 36 open reading frames was introduced into Streptomyces lividans TK23. The transformant was confirmed to express the biosynthetic genes and produce saprolmycins by liquid chromatography–mass spectrometry analysis of the extract.     

Streptomyces daliensis sp. nov. from soil

A novel actinomycete strain YIM 31724^T was isolated from a soil sample collected from Dali, Yunnan Province, People’s Republic of China. The strain is characterized by white to yellow white aerial mycelia, spiral spore chains and smooth spore surface. The cell wall of strain YIM 31724^T contained LL-diaminopimelic acid (A₂pm) and traces of meso-A₂pm. Whole-cell hydrolysates contained mainly glucose and small amounts of galactose and xylose. The menaquinones were MK-9(H₆) (31%) and MK-9(H₈) (69%). Phosphatidylethanolamine was the diagnostic phospholipid. The DNA G+C content of strain YIM 31724^T was 67.2 mol%. Phylogenetic analysis indicated that the strain belongs to the genus Streptomyces, with highest similarity to Streptomyces rimosus subsp. rimosus JCM 4667^T (rRNA gene sequence similarity value of 98.9%) and Streptomyces erumpens DSM 40941^T (rRNA gene sequence similarity value of 98.7%). Based on its phenotypic and genotypic characteristics, including low DNA–DNA hybridization results, strain is proposed as the type strain of a novel species, Streptomyces daliensis sp. nov.     

海洋链霉菌Streptomyces sp.SCSIO 1667中吲哚咔唑生物碱类成分的研究

运用大孔树脂柱及硅胶柱层析对南海海洋链霉菌Streptomyces sp.SCSIO 1667的代谢产物进行了研究,从SCSIO 1667菌株的发酵产物中分离得到两个indolocarbazole生物碱类化合物,经质谱,1D、2D NMR波谱数据分析鉴定为星形孢菌素(staurosporine,1)和K-252d(2)。     

Production and characterization of thermostable xylanase and pectinase from Streptomyces sp. QG-11-3

Streptomyces sp. QG-11-3, which produces a cellulase-free thermostable xylanase (96 IU ml⁻¹) and a pectinase (46 IU ml⁻¹), was isolated on Horikoshi medium supplemented with 1% w/v wheat bran. Carbon sources that favored xylanase production were rice bran (82 IU ml⁻¹) and birch-wood xylan (81 IU ml⁻¹); pectinase production was also stimulated by pectin and cotton seed cake (34 IU ml⁻¹ each). The partially purified xylanase and pectinase were optimally active at 60°C. Both enzymes were 100% stable at 50°C for more than 24 h. The half-lives of xylanase and pectinase at 70, 75 and 80°C were 90, 75 and 9 min, and 90, 53 and 7 min, respectively. The optimum pH values for xylanase and pectinase were 8.6 and 3.0, respectively, at 60°C. Xylanase and pectinase were stable over a broad pH range between 5.4 and 9.4 and 2.0 to 9.0, respectively, retaining more than 85% of their activity. Ca²⁺ stimulated the activity of both enzymes up to 7%, whereas Cd²⁺, Co²⁺, Cr³⁺, iodoacetic acid and iodoacetamide inhibited xylanase up to 35% and pectinase up to 63%; at 1 mM, Hg²⁺ inhibited both enzymes completely. Journal of Industrial Microbiology & Biotechnology (2000) 24, 396–402. Received 29 September 1999/ Accepted in revised form 02 February 2000     

链霉菌来源D-甘露糖异构酶的性质及其在制备D-甘露糖中的应用

[背景]D-甘露糖具有多种功能活性,在食品、医药、饲料等行业应用广泛.D-甘露糖异构酶可以催化D-果糖与D-甘露糖之间的相互转化,在D-甘露糖的酶法制备中具有应用潜力.[目的]克隆一个链霉菌(Streptomyces sp.)来源的D-甘露糖异构酶基因(sssMIaseA)并在大肠杆菌中表达,研究其酶学性质,并用于制备...     

Cloning and Nucleotide Sequence of the Mycodextranase Gene from Streptomyces sp. J-13-3

Mycodextranase (EC 3.2.1.61) is an α-glucanase that cleaves α-1,4-bonds of alternating α-1,3- and α-1,4-linked D-glucan (nigeran). The gene encoding mycodextranase from Streptomyces sp. J-13-3 was cloned by hybridization with a degenerate oligonucleotide probe from the amino-terminal amino acid sequence of the enzyme and its nucleotide structure was analyzed. The open reading frame consisted of 1,803 base pairs encoding a signal peptide of 60 amino acids and a mature protein of 540 amino acids with a calculated molecular weight of 56,078. The deduced amino acid sequence showed weak similality to a chitinase homolog from Streptomyces lividans and a chitinase from Xanthomonas sp.     

Purification and Characterization of a Novel (R)-Imine Reductase from Streptomyces sp. GF3587

The (R)-imine reductase (RIR) of Streptomyces sp. GF3587 was purified and characterized. It was found to be a NADPH-dependent enzyme, and was found to be a homodimer consisting of 32 kDa subunits. Enzymatic reduction of 10 mM 2-methyl-1-pyrroline (2-MPN) resulted in the formation of 9.8 mM (R)-2-methylpyrrolidine ((R)-2-MP) with 99% e.e. The enzyme showed not only reduction activity for 2-MPN at neutral pH (6.5–8.0), but also oxidation activity for (R)-2-MP under alkaline pH (10–11.5) conditions. It appeared to be a sulfhydryl enzyme based on the sensitivity to sulfhydryl specific inhibitors. It was very specific to 2-MPN as substrate.