Molecular cloning, expression and characterization of protein disulfide isomerase from Conus marmoreus

The oxidative folding of disulfide-rich conotoxins is essential for their biological functions. In vivo, disulfide bond formation is mainly catalyzed by protein disulfide isomerase. To elucidate the physiologic roles of protein disulfide isomerase in the folding of conotoxins, we have cloned a novel full-length protein disulfide isomerase from Conus marmoreus. Its ORF encodes a 500 amino acid protein that shares sequence homology with protein disulfide isomerases from other species, and 70% homology with human protein disulfide isomerase. Enzymatic analyses of recombinant C. marmoreus protein disulfide isomerase showed that it shared functional similarities with human protein disulfide isomerase. Using conotoxins tx3a and sTx3.1 as substrate, we analyzed the oxidase and isomerase activities of the C. marmoreus protein disulfide isomerase and found that it was much more efficient than glutathione in catalyzing oxidative folding and disulfide isomerization of conotoxins. We further demonstrated that macromolecular crowding had little effect on the protein disulfide isomerase-catalyzed oxidative folding and disulfide isomerization of conotoxins. On the basis of these data, we propose that the C. marmoreus protein disulfide isomerase plays a key role during in vivo folding of conotoxins.     

生物转化生产D-塔格糖的食品级菌种选育及L-阿拉伯糖异构酶的克隆表达

L-阿拉伯糖异构酶(L-arabinose isomerase,L-AI)是一种可以催化D-半乳糖为D-塔格糖的胞内异构化酶。随着塔格糖在食品工业中越来越广泛的应用,能够将半乳糖转化为塔格糖的食品级微生物以及食品级来源的L-AI受到更大的关注。文中从各种酸奶制品、泡菜及其他一些食品中采集不同的样品,筛选出1株具有L-AI酶活的食品级菌株,经过生理生化鉴定以及16S rDNA序列测定,确定该菌株为戊糖片球菌,命名为Pediococcus pentosaceus PC-5。以该菌基因组为模板,克隆L-AI基因,并在大肠杆菌BL21成功地异源表达。表达产物经粗提取后,在40℃下加入Mn2+,使D-半乳糖转化为D-塔格糖的转化率为33%。     

Chicken deoxyribonuclease: purification,characterization, gene cloning and gene expression

Chicken DNase was purified to apparent homogeneity from the pancreas extract. It showed two isoforms, A and B forms, on cation-exchange chromatography. On SDS-PAGE it was a 30-kDa protein. When analyzed on an electrospray-mass analyzer, form A showed a major mass peak of 30859, and form B, 30882. The enzyme was bound to concanavalin A, indicating its glycoprotein nature. The carbohydrate side chain could be removed by endoglycosidase F. Chicken DNase was activated by metal ions and for half-maximum activation, Mn²⁺ and Mg²⁺ required were 1 mM and 4 mM, respectively. The pH optimum was between 7 and 8 depending on the metal ions used. In the presence of Cu²⁺, it was almost completely inactivated by 0.1 M iodoacetate within 1 min. In the absence of Ca²⁺ at pH 8, chicken DNase resisted to the trypsin or -mercaptoethenol inactivation. When the purified enzyme was subjected to protein sequencing, 93% of the sequence was established. Based on the amino acid sequence, the cDNA of chicken DNase was amplified, cloned and sequenced. The cDNA sequence consisted of 1079 nucleotides in which 67 were of the 5-untranslated region and 166 of the 3 and, in the 5-untranslated region, two types of sequences occurred. The polypeptide chain of 282 amino acids, translated from the open reading frame, was composed of the mature protein of 262 amino acids and a putative signal peptide of 20 amino acids. As compared with mammalian DNases, chicken DNase had an overall 58 ± 61% sequence identity, one less potential N-glycosylation site, and one extra disulfide. The cDNA was cloned into the pET15b expression vector. When induced, active recombinant chicken DNase was expressed in Escherichia coli strain BL21(DE3)pLysS and was present in the insoluble fraction of cell lysates.     

An extracellular exo-beta-(1,3)-glucanase from Pichia pastoris: purification, characterization, molecular cloning, and functional expression

An extracellular exo-beta-(1,3)-glucanase (designated EXG1) was purified to apparent homogeneity from Pichia pastoris X-33 cultures by ammonium sulfate fractionation, ion-exchange chromatography, and gel filtration. The native enzyme is unglycosylated and monomeric with a molecular mass of approximately 47kDa. At its optimal pH of 6.0, the enzyme shows highest activity among physiological substrates toward laminarin (apparent Km, 3.5 mg/ml; Vmax, 192 micromole glucose produced/min/mg protein) but also hydrolyzes amygdalin and esculin, and the chromogenic substrates p-nitrophenyl-beta-D-glucopyranoside and p-nitrophenyl-beta-D-xylopyranoside. The P. pastoris EXG1 gene was cloned by a PCR-based strategy using genomic DNA as template. This intronless gene predicts an ORF that encodes a primary translation product of 414 amino acids. We believe that this preproprotein is processed sequentially by signal peptidase and a Kex2-like endoprotease to yield a mature protein of 392 amino acids (45,376 Da; pI, 4.46) that shares 36-64% amino acid identity with other yeast exo-beta-(1,3)-glucanases belonging to Glycoside Hydrolase Family 5. It also possesses the eight invariant residues and signature pattern [LIV]-[LIVMFYWGA](2)-[DNEQG]-[LIVMGST]-X-N-E-[PV]-[RHDNSTLIVFY] shown by all Family 5 members. Overexpression of the cloned EXG1 gene in Pichia cells, followed by Ni-CAM HC resin chromatography, yielded milligram quantities of homogeneous recombinant EXG1 in active form for further characterization studies.     

Molecular cloning, expression, purification and characterization of calcineurin from bovine cardiac muscle

Calcineurin (CaN), also known as calmodulin-dependent phosphatase, was cloned from bovine cardiac muscle and the deduced amino acid sequences of CaN A revealed that it had an open reading frame of 511 amino acid residues. As compared to bovine brain CaN A, the cardiac enzyme contains a 10 amino acid (ATVEAIEADE) deletion before the autoinhibitory region. A deletion analysis of the catalytic domain revealed a 20% decrease in phosphatase activity when the N-terminal 200 amino acids were removed from CaN A as compared to the wild type enzyme. The C-terminal deletions of CaN A revealed that in addition to the autoinhibitory domain (residues 457-480), additional adjacent residues (407-456) also inhibited CaN activity. These results point to either a second autoinhibitory region within CaN A or an extension of the previously noted autoinhibitory region within the cardiac CaN A enzyme.     

Multiple isoforms of choline kinase from Caenorhabditis elegans: cloning,expression, purification,and characterization

Choline kinase is the first enzymatic step in the CDP-choline pathway for phosphatidylcholine biosynthesis. The genome of the nematode, Caenorhabditis elegans, contains seven genes that appear likely to encode choline and/or ethanolamine kinases. We cloned five and expressed four of these genes, and purified or partially purified three of the encoded enzymes. All expressed proteins had choline kinase activity; those that most closely resemble the mammalian choline kinases were the most active. CKA-2, a very active form, was purified to near homogeneity. The K(m) values for CKA-2 were 1.6 and 2.4 mM for choline and ATP, respectively, and k(cat) was 74 s(-1). CKA-2 was predominantly a homodimer as assessed by glycerol gradient sedimentation and dynamic light scattering. CKB-2, which was less similar to mammalian choline kinases, had K(m) values for choline and ATP of 13 and 0.7 mM, and k(cat) was 3.8 s(-1). Both of these highly purified enzymes required magnesium, had very alkaline pH optima, and were much more active with choline as substrate than with ethanolamine. These results provide a foundation for future studies on the structure and function of choline kinases, as well as studies on the genetic analysis of the function of the multiple isoforms in this organism.     

A-protein from achromogenic atypical Aeromonas salmonicida: molecular cloning, expression, purification, and characterization.

Achromogenic atypical Aeromonas salmonicida is the causative agent of goldfish ulcer disease. Virulence of this bacterium is associated with the production of a paracrystalline outer membrane A-layer protein. The species-specific structural gene for the monomeric form of A-protein was cloned into a pET-3d plasmid in order to express and produce a recombinant form of the protein in Escherichia coli BL21(DE3). The induced protein was isolated from inclusion bodies by a simple solubilization-renaturation procedure and purified by ion exchange chromatography on Q-Sepharose to over 95% pure monomeric protein. Recombinant A-protein was compared by biochemical, immunological, and molecular methods with the A-protein isolated from atypical A. salmonicida bacterial cells by the glycine and the membrane extraction methods. The recombinant form was found to be undistinguishable from the wild type when examined by SDS-PAGE and gel filtration chromatography. The immunological similarity of the protein samples was demonstrated by employing polyclonal and monoclonal antibodies in ELISA and Western blot techniques. All forms of A-protein were found to activate the secretion of tumor necrosis factor alpha from murine macrophage. To date, this represents the first large-scale production of biologically active recombinant A-protein.     

An exodeoxyribonuclease from Streptomyces coelicolor: expression, purification and biochemical characterization

Streptomyces coelicolor A3(2) produces several intra and extracellular enzymes with deoxyribonuclease activities. The examined N-terminal amino acid sequence of one of extracellular DNAases (TVTSVNVNGLL) and database search on S. coelicolor genome showed a significant homology to the putative secreted exodeoxyribonuclease. The corresponding gene (exoSc) was amplified, cloned, expressed in Escherichia coli, purified to homogeneity and characterized. Exonuclease recExoSc degraded chromosomal, linear dsDNA with 3'-overhang ends, linear ssDNA and did not digest linear dsDNA with blunt ends, supercoiled plasmid ds nor ssDNA. The substrate specificity of recExoSc was in the order of dsDNA>ssDNA>3'-dAMP. The purified recExoSc was not a metalloprotein and exhibited neither phosphodiesterase nor RNase activity. It acted as 3'-phosphomonoesterase only at 3'-dAMP as a substrate. The optimal temperature for its activity was 57 degrees C in Tris-HCl buffer at optimal pH=7.5 for either ssDNA or dsDNA substrates. It required a divalent cation (Mg(2+), Co(2+), Ca(2+)) and its activity was strongly inhibited in the presence of Zn(2+), Hg(2+), chelating agents or iodoacetate.     

Purification, characterization, cloning, and expression of a glutamic acid-specific protease from Bacillus licheniformis ATCC 14580.

A glutamic acid-specific protease has been purified to homogeneity from Bacillus licheniformis ATCC 14580 utilizing Phe-Leu-D-Glu-OMe-Sepharose affinity chromatography and crystallized. The molecular weight of the protease was estimated to be approximately 25,000 by SDS-polyacrylamide gel electrophoresis. This protease, which we propose to call BLase (glutamic acid-specific protease from B. licheniformis ATCC 14580), was characterized enzymatically. Using human parathyroid hormone (13-34) and p-nitroanilides of peptidyl glutamic acid and aspartic acid, we found a marked difference between BLase and V8 protease, EC 3.4.21.9, although both proteases showed higher reactivity for glutamyl bonds than for aspartyl bonds. Diisopropyl fluorophosphate and benzyloxycarbonyl Leu-Glu chloromethyl ketone completely inhibited BLase, whereas EDTA reversibly inactivated the enzyme. The findings clearly indicate that BLase can be classified as a serine protease. To elucidate the complete primary structure and precursor of BLase, its gene was cloned from the genomic DNA of B. licheniformis ATCC 14580, and the nucleotide sequence was determined. Taking the amino-terminal amino acid sequence of the purified BLase into consideration, the clones encode a mature peptide of 222 amino acids, which follows a prepropeptide of 94 residues. The recombinant BLase was expressed in Bacillus subtilis and purified to homogeneity. Its key physical and chemical characteristics were the same as those of the wild-type enzyme. BLase was confirmed to be a protease specific for glutamic acid, and the primary structure deduced from the cDNA sequence was found to be identical with that of a glutamic acid-specific endopeptidase isolated from Alcalase (Svendsen, I., and Breddam, K. (1992) Eur. J. Biochem. 204, 165-171), being different from V8 protease and the Glu-specific protease of Streptomyces griseus which consist of 268 and 188 amino acids, respectively.     

Molecular cloning, expression, purification, and characterization of fructose-1,6-bisphosphate aldolase from Thermus aquaticus

Fructose-1,6-bisphosphate aldolase from the thermophilic eubacteria, Thermus aquaticus YT-1, was cloned and sequenced. Nucleotide-sequence analysis revealed an open reading frame coding for a 33-kDa protein of 305 amino acids having amino acid sequence typical of thermophilic adaptation. Multiple sequence alignment classifies the enzyme as a class II B aldolase that shares similarity with aldolases from other extremophiles: Thermotoga maritima, Aquifex aeolicus, and Helicobacter pylori (49--54% identity, 76--81% homology). Taq FBP aldolase was overexpressed under tac promoter control in Escherichia coli and purified to homogeneity using heat treatment followed by two chromatographic steps. Yields of 40--50 mg of monodisperse protein were obtained per liter of culture. The quaternary structure is that of a homotetramer stabilized by an apparent 21-amino-acid insertion sequence. The recombinant protein is thermostable for at least 45 min at 80 degrees C with little residual activity below 60 degrees C. Kinetic characterization at 70 degrees C, the optimal growth temperature for T. aquaticus, indicates extreme negative subunit cooperativity (h = 0.32) with a limiting K(m) of 305 microM. The maximal specific activity (V(max)) is 46 U/mg at 70 degrees C.     

A novel galactolipase from a green microalga Chlorella kessleri: purification,characterization, molecular cloning,and heterologous expression

We have identified an enzyme, galactolipase (ckGL), which hydrolyzes the acyl ester bond of galactolipids such as digalactosyldiacylglycerol (DGDG), in the microalga Chlorella kessleri. Following purification of the enzyme to electrophoretic homogeneity from cell-free extract, the maximum activity toward DGDG was observed at pH 6.5 and 37 °C. ckGL was Ca²⁺-dependent enzyme and displayed an apparent molecular mass of approx. 53 kDa on SDS-PAGE. The substrate specificity was in the order: DGDG (100%) > monogalactosyldiacylglycerol ≈ phosphatidylglycerol (~ 40%) > sulfoquinovosyldiacylglycerol (~ 20%); the enzyme exhibited almost no activity toward glycerides and other phospholipids. Gas chromatography analysis demonstrated that ckGL preferably hydrolyzed the sn-1 acyl ester bond in the substrates. The genomic DNA sequence (5.6 kb) containing the ckGL gene (designated glp1) was determined and the cDNA was cloned. glp1 was composed of 10 introns and 11 exons, and the 1608-bp full-length cDNA encoded a mature ckGL containing 475 amino acids (aa), with a presequence (60 aa) containing a potential chloroplast transit peptide. Recombinant functional ckGL was produced in Escherichia coli. Although the deduced aa sequence of ckGL contained the typical GXSXG motif of serine hydrolases together with conserved histidine and aspartate residues which would form part of the catalytic triad of α/β-hydrolases, ckGL showed no significant overall similarity with known lipases including GLs from Chlamydomonas reinhardtii and Aspergillus japonicus, indicating that ckGL is a novel GL. ckGL, with high specificity for DGDG, could be applicable to food processing as an enzyme capable of improving material textures.

     

Collagenolytic serine-carboxyl proteinase from Alicyclobacillus sendaiensis strain NTAP-1: purification,characterization, gene cloning,and heterologous expression

Enzymatic degradation of collagen produces peptides, the collagen peptides, which show a variety of bioactivities of industrial interest. Alicyclobacillus sendaiensis strain NTAP-1, a slightly thermophilic, acidophilic bacterium, extracellularly produces a novel thermostable collagenolytic activity, which exhibits its optimum at the acidic region (pH 3.9) and is potentially applicable to the efficient production of such peptides. Here, we describe the purification to homogeneity, characterization, gene cloning, and heterologous expression of this enzyme, which we call ScpA. Purified ScpA is a monomeric, pepstatin-insensitive carboxyl proteinase with a molecular mass of 37 kDa which exhibited the highest reactivity toward collagen (type I, from a bovine Achilles tendon) among the macromolecular substrates examined. On the basis of the sequences of the peptides obtained by digestion of collagen with ScpA, the following synthetic peptides were designed as substrates for ScpA and kinetically analyzed: Phe-Gly-Pro-Ala*Gly-Pro-Ile-Gly (k(cat), 5.41 s(-1); K(m), 32 micro M) and Met-Gly-Pro-Arg*Gly-Phe-Pro-Gly-Ser (k(cat), 351 s(-1); K(m), 214 micro M), where the asterisks denote the scissile bonds. The cloned scpA gene encoded a protein of 553 amino acids with a calculated molecular mass of 57,167 Da. Heterologous expression of the scpA gene in the Escherichia coli cells yielded a mature 37-kDa species after a two-step proteolytic cleavage of the precursor protein. Sequencing of the scpA gene revealed that ScpA was a collagenolytic member of the serine-carboxyl proteinase family (the S53 family according to the MEROPS database), which is a recently identified proteinase family on the basis of crystallography results. Unexpectedly, ScpA was highly similar to a member of this family, kumamolysin, whose specificity toward macromolecular substrates has not been defined.     

拟南芥阿拉伯糖-5-磷酸异构酶的原核表达、纯化及酶催化特性

阿拉伯糖-5-磷酸异构酶(Kds D)是2-酮-3-脱氧辛糖酸(KDO)生物合成途径的第一个关键限速酶,通过无缝克隆技术将拟南芥Kds D基因构建至原核表达载体p ET-HTT,经过IPTG诱导,在大肠杆菌BL21(DE3)中获得了大量重组蛋白的可溶性表达;表达产物经Ni-NTA亲和层析和分子筛层析(SEC)方法进行酶蛋白的分离纯化步骤,得到纯度85%以上的高纯度酶;分子筛层析结果发现纯化后的目的蛋白Kds D在溶液中主要以多聚体、二聚体和单体形式存在,这同微生物来源Kds D酶在溶液中以四聚体形式存在很大差异;进一步使用Western blotting和MALDI-TOF MASS技术对纯化的蛋白进行鉴定;测定了拟南芥Kds D酶学性质,证明该酶催化反应的最适p H值为8.0,最适作用温度为37℃,各种金属离子在低浓度均对酶活性存在不同程度的抑制作用,其中以Co~(2+)、Cd~(2+)对酶活性的抑制作用最强,而5 mmol/L金属螯合剂EDTA对酶有激活作用。此外,以阿拉伯糖-5-磷酸(A5P)为底物时,拟南芥Kds D酶动力学常数Vmax和Km值分别为0.18 mmol/(L·min)、0.16 mmol/L,比较发现该酶与底物的亲和性高于大肠杆菌Kds D。以上研究结果为Kds D蛋白结构与功能及其在新型抗生素研制领域中的工业化应用奠定了基础。     

Homologous expression,purification and characterization of a novel high-alkaline and thermal stable lipase from Burkholderia cepacia ATCC 25416

The lipase secreted by Burkholderia cepacia ATCC 25416 was particularly attractive in detergent and leather industry due to its specific characteristics of high alkaline and thermal stability. The lipase gene (lipA), lipase chaperone gene (lipB), and native promoter upstream of lipA were cloned. The lipA was composed of 1095 bp, corresponding to 364 amino acid residues. The lipB located immediately downstream of lipA was composed of 1035 bp, corresponding to 344 amino acid residues. The lipase operon was inserted into broad host vector pBBRMCS1 and electroporated into original strain. The homologous expression of recombinant strain showed a significant increase in the lipase activity. LipA was purified by three-step procedure of ammonium sulfate precipitation, phenyl-sepharose FF and DEAE-sepharose FF. SDS-PAGE showed the molecular mass of the lipase was 33 kDa. The enzyme optimal temperature and pH were 60 °C and 11.0, respectively. The enzyme was stable at 30–70 °C. After incubated in 70 °C for 1 h, enzyme remained 72% of its maximal activity. The enzyme exhibited a good stability at pH 9.0–11.5. The lipase preferentially hydrolyzed medium-chain fatty acid esters. The enzyme was strongly activated by Mg²⁺, Ca²⁺, Cu²⁺, Zn²⁺, Co²⁺, and apparently inhibited by PMSF, EDTA and also DTT with SDS. The enzyme was compatible with various ionic and non-ionic surfactants as well as oxidant H₂O₂. The enzyme had good stability in the low- and non-polar solvents.     

S-adenosylhomocysteine hydrolase from Corynebacterium glutamicum: cloning, overexpression, purification, and biochemical characterization

The S-adenosylhomocysteine hydrolase gene (sahase) was cloned from the Gram-positive soil bacterium Corynebacterium glutamicum (ATCC 13032) and sequenced. The sahase gene possesses an open reading frame, which consists of 1,434 nucleotides that encode 478 amino acids. The sahase gene from C. glutamicum was expressed in Escherichia coli Rosetta cells by inserting the 1,434-bp fragment downstream from the isopropyl-beta-D-thiogalactopyranoside-inducible promoter of the pET28a+ expression vector. The recombinant S-adenosylhomocysteine hydrolase from C. glutamicum (CgrSAHase) was purified efficiently by a two-step procedure, tangential ultrafiltration and affinity chromatography. The molecular weight of the CgrSAHase, estimated by gel filtration, was about 210 kDa, while sodium dodecyl sulfate polyacrylamide gel electrophoresis yielded a relative molecular mass of 52 +/- 1 kDa. The Michaelis-Menten constants for the natural substrates of the enzyme, S-adenosylhomocysteine (SAH), adenosine, and homocysteine, were determined to be 12, 1.4, and 40 microM, respectively. The overexpression of CgrSAHase was achieved at high level (>40 mg protein/g wet cells). Because of its high capacity to synthesize SAH, this enzyme is of high biotechnological interest.     

Four glucosyltransferases from rice: cDNA cloning, expression, and characterization

Four UDP-dependent glucosyltransferase (UGT) genes, UGT706C1, UGT706D1, UGT707A3, and UGT709A4 were cloned from rice, expressed in Escherichia coli, and purified to homogeneity. In order to find out whether these enzymes could use flavonoids as glucose acceptors, apigenin, daidzein, genistein, kaempferol, luteolin, naringenin, and quercetin were used as potential glucose acceptors. UGT706C1 and UGT707A3 could use kaempferol and quercetin as glucose acceptors and the major glycosylation position was the hydroxyl group of carbon 3 based on the comparison of HPLC retention times, UV spectra, and NMR spectra with those of corresponding authentic flavonoid 3-O-glucosides. On the other hand, UGT709A4 only used the isoflavonoids genistein and daidzein and transferred glucose onto 7-hydroxyl group. In addition, UGT706D1 used a broad range of flavonoids including flavone, flavanone, flavonol, and isoflavone, and produced at least two products with glycosylation at different hydroxyl groups. Based on their substrate preferences and the flavonoids present in rice, the in vivo function of UGT706C1, UGT706D1, and UGT707A3 is most likely the biosynthesis of kaempferol and quercetin glucosides.