ABSTRACT
Transketolase (EC 2.2.1.1, TK) is a thiamine diphosphate-dependent enzyme that catalyzes the transfer of a two-carbon hydroxyacetyl unit with reversible C-C bond cleavage and formation. It is widely used in the production of chemicals, drug precursors, and asymmetric synthesis by cascade enzyme catalysis. In this paper, the activity of transketolase TKTA from Escherichia coli K12 on non-phosphorylated substrates was enhanced through site-directed saturation mutation and combined mutation. On this basis, the synthesis of tartaric semialdehyde was explored. The results showed that the optimal reaction temperature and pH of TKTA_M (R358I/H461S/R520Q) were 32 ℃ and 7.0, respectively. The specific activity on d-glyceraldehyde was (6.57±0.14) U/mg, which was 9.25 times higher than that of the wild type ((0.71±0.02) U/mg). Based on the characterization of TKTA_M, tartaric acid semialdehyde was synthesized with 50 mmol/L 5-keto-d-gluconate and 50 mmol/L non-phosphorylated ethanolaldehyde. The final yield of tartaric acid semialdehyde was 3.71 g with a molar conversion rate of 55.34%. Hence, the results may facilitate the preparation of l-(+)-tartaric acid from biomass, and provide an example for transketolase-catalyzed non-phosphorylated substrates.
Subject(s)
Escherichia coli/genetics , Transketolase/chemistry , Tartrates , Escherichia coli Proteins/geneticsABSTRACT
L-asparaginase hydrolyzes L-asparagine to produce L-aspartic acid and ammonia. It is widely distributed in microorganisms, plants and serum of some rodents, and has important applications in the pharmaceutical and food industries. However, the poor thermal stability, low catalytic efficiency and low yield hampered the further application of L-asparaginase. In this paper, rational design and 5' untranslated region (5'UTR) design strategies were used to increase the specific enzyme activity and protein expression of L-asparaginase derived from Rhizomucor miehei (RmAsnase). The results showed that among the six mutants constructed through homology modeling combined with sequence alignment, the specific enzyme activity of the mutant A344E was 1.5 times higher than the wild type. Subsequently, a food-safe strain Bacillus subtilis 168/pMA5-A344E was constructed, and the UTR strategy was used for the construction of recombinant strain B. subtilis 168/pMA5 UTR-A344E. The enzyme activity of B. subtilis 168/pMA5 UTR-A344E was 7.2 times higher than that of B. subtilis 168/pMA5-A344E. The recombinant strain B. subtilis 168/pMA5 UTR-A344E was scaled up in 5 L fermenter, and the final yield of L-asparaginase was 489.1 U/mL, showing great potential for industrial application.
Subject(s)
Asparaginase/genetics , Bacillus subtilis/genetics , Industrial Microbiology , Protein Engineering , Rhizomucor/enzymology , Sequence AlignmentABSTRACT
Objective:To investigate the molecular mechanism of VRC01 resistance in HIV-1 subtype B′ strains isolated from a patient (DRVI01) with broadly neutralizing antibody (bNAb).Methods:Sequences of the HIV-1 subtype B′ strains isolated from patient DRVI01 were compared with those of HIV-1 subtype B′ strains that were isolated at the same time but sensitive to VRC01 antibody. Key amino acids that might affect the neutralization of VRC01 were selected according to literature reports. Effects of the selected amino acids on VRC01 neutralization were verified by site-directed mutation and sequence exchange of membrane proteins from different patients.Results:Single-point mutations of E279D and R282K in LoopD region and N460A and N463Q in V5 region reversed the viral sensitivity to VRC01 neutralization. Combined mutations in two or three above-mentioned sites significantly increased the viral sensitivity to VRC01 antibody compared with single-point mutations. Contrary to literature reports, the glycosylation site mutation of N276 had no influence on the viral sensitivity to VRC01.Conclusions:HIV-1 subtype B′ strains isolated from patient DRV01 with bNAb carried the mutations of D279 and K282 in LoopD region and N460 and N463 in V5 region, resulting in resistance to VRC01 antibody.
ABSTRACT
Objective To construct a highly efficient approach to the introduction of the single-base mutation in a plasmid containing the adenovirus whole genome larger than 40 kb.Methods The target DNA with a mutation site was achieved by over-lapping PCR.The large plasmid with adenovirus genome and target DNA were co-transformed into Escherichia coli strain DY330 carrying a high rate Red recombination system.The positive clone was selected via colony PCR in combination with enzyme identification.The site-mutation large plasmid was transformed into E.coli strain DH10B in which the backbone of the large plasmid remained was stable.Results Two mutations were continuously introduced into the adenovirus genome,the location of which was pos.9171 and pos.24410 respectively.The integrality and stability of the plasmid backbone were verified by enzyme cutting identification.The two mutations on the plasmid were verified by DNA sequencing.Conclusion An efficient approach to the introduction of the single-base mutation in positions 9171 and 24410 from the adenovirus genome which was integrated into a plasmid is successfully established.The positive selection efficiency ranges from 5%to 15%.The construction of the approach will facilitate the study of adenovirus infection mechanism.
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OBJECTIVE: To construct the point mutants of α3* nicotine acetylcholine receptors (nAChRs), optimize the method of receptor mutagenesis and investigate the function of the mutants by using the agonist acetycholine (Ach). METHODS: The α3* nAChRs mutants were constructed by PCR mediated site-directed mutation techniques. Point mutated primers were designed according to rat α3 subunit gene. The cRNA of α3 subunit point mutant was synthesized by in vitro transcription. The expression of mutants in Xenopus oocytes were detected by two-electrode voltage-clamp techniques. Gating properties of the two mutants were detected by Ach. RESULTS: Mutants of α3β2 and α3β4 nAChRs subtypes were constructed successfully. The half effective concentrations (EC50) of wild types α3β2 and α3β4 nAChRs were 55.33 and 163.00 μmol·L-1, respectively. While the EC50 of α3(S147T)β2 and α3(S147T)β4 nAChRs mutants were 33.10 and 121.10 μmol·L-1, respectively. CONCLUSION: The construction of mutation from the 147th serine to threonine of α3 subunit can provide a function model to make more other receptor mutants, and would be helpful to interrogate the interaction between drug and α3* nAChR.
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Objective:To construct a mutant D314A of Escherichia coli cytosine deaminase (EC-CD, substitution of an alanine (A) for the aspartic acid (D) at position 314 of cytosine deaminase) and investigate its antitumor effect. Methods: Eukaryotic expression plasmid containing EC-CD gene (pcDNA3.1-CD~(wt)) was constructed, and the mutant pcDNA3.1-CD~(D314A) plasmid, with aspartic acid (D) at position 314 of EC-CD gene substituted by alanine (A) (EC-CD~(D314A)), was established by site-directed mutation. EC-CD~(wt) and EC-CD~(D314A) were transfected into human colon cancer cell line LoVo via Lipofectamine~(tm) 2000, and positive LoVo-CD~(wt) and LoVo-CD~(D314A) cells stably expressing corresponding genes were selected by G418. The cytotoxicity and bystander effects of EC-CD and EC-CD~(D314A) genes on LoVo cells were e-valuated by MTT assay. Results: The mutant D314A was confirmed by sequence analysis. EC-CD and EC-CD~(D314A) mRNA were expressed after transfected into LoVo cells. The IC_(50) of Lovo-CD~(D314A) cells was (85.13±0.60) mmol/L, which was significantly lower than that of LoVo-CD~(wt) cells ([689.76±0.45] μmol/L, P=0.000). Bystander effect assay showed that, when at the ratio of 30%, the survival rates of LoVo-CD~(wt) cells and Lovo-CD~(D314A) cells were (48.5±0.49)% and (17.3±0.40) % (P = 0.000), respectively. Conclusion: Mutatant EC-CD gene (EC-CD~(D314A)) has a significantly in-creased antitumor effect on LoVo cells compared with wild type EG-CD gene, and it may become a new candidate gene for tumor gene therapy.
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In order to obtain three isoforms of apolipoprotein E (apoE), the cDNA encoding apoE3 was obtained by RT-PCR from normal human liver tissue. Site-directed mutagenesis was used to obtain the cDNAs encoding apoE2 and apoE4 isoforms. The 3 cDNAs were subcloned into vector pGEM-3Z and verified by DNA sequencing. The expression recombinant which can express the target protein as a (His) 6-tagged fusion was constructed by subcloning apoE cDNA into vector pT7-PL. The purified proteins were gained by Ni-NTA column. The SDS-PAGE results revealed the 6 His fusion proteins (apoE2, apoE3 and apoE4) were correctly expressed and purified successfully.
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Objective To construct eukaryotic expression vector of HPV18 L1- E6, E7 chimeric gene and examine the humoral and cellular immune responses induced by this DNA vaccines in mice. Methods The C-terminal of major capsid protein L1 gene and mutant zinc finger domains of early E6/7 oncogenes in HPV18 were integrated and inserted into eukaryotic expression vector pVAX1 to generate vaccines pVAX1-L1E6Mxx, E7Mxx. CHO cells were transiently transfected with the individual construct. Target protein expressions in the lysate of the transfected cells were measured by ELISA and immunocytochemistry. After BALB/c mice were vaccinated with various recombinant plasmids(pVAX1-L1-E6M3 or pVAX1-L1-E7M3) and immunie adjuvants (pLXHDmB7-2 or LTB) through different administration routes (intramuscular or intranasal) , the great cellular immune responses were produced as revealed by delayed-type hypersensitivity (DTH) and lymphocyte proliferation, and the expression of IL-4 and IFN- γ cells in CD4+ and CD8+subpopulations. Results The highly efficient expression of pVAX1-L1E6Mxx, E7Mxx vector in host eukaryotic cells were demonstrated both by ELISA and immunocytochemistry. The level of specific serum IgG against HPV in experiment groups mice was much higher than that of control group, and intranuscular immunization group had the highest antibody level. Intramuscular immunization groups were superior to intranasal immunization groups in DTH response, splenocyte proliferation and CD8+ IFN-γ + cells number, but CD4+ IL4+ cell number was higher in intranasal immunization groups. The immunization groups using pLXHDmB7-2 as adjuvant were superior to other groups in immunoresponse. Conclusion These DNA vaccines produce remarkable cellular and humoral immuneresponses in the mouse and may provide as prophylatic and therapeutic candidates for HPV induced cancer treatment.
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Objective:To determine the region of human transmembrane tumor necrosis factor alpha (TM TNF?),essential for cytotoxic activity against mouse L929 cell.Methods:Single amino acid substituted TM TNF? mutant proteins(muteins) were produced by in vitro transcription linked translation techniques.An expression cDNA for TM TNF? was site directed mutagenized by recombinant PCR.7 single amino acid substituted TM TNF? muteins were generated and assayed for cytotoxic activity.Results:The cytotoxic activities of TM TNF? muteins,eg,TM TNF? -71/Lys was