Construction of a Saccharopolyspora erythraea mutant producing erythromycin B as its major fermentation product / 军事医学科学院院刊

Objective:To obtain a large amount of erythromycin B and to investigate the activity site in eryK. Methods:The key sequence of the BC loop region in eryK gene was knocked out and the eryK gene with 101 bp deleted was amplified by overlapping PCR,and cloned into vector pWHM3 to construct recombinant plasmid. The Saccharopolyspora erythraea mutant AK17 was constructed through chromosomal homologous recombination technique.Results and Conclusions:The S.erythraea mutant AK17 was constructed. The results of TCL and MS analysis showed that the major fermentation product of AK17 is erythromycin B.

Construction and expression of humanized anti-EGFR antibody / 军事医学科学院院刊

Objective:To express rationally engineered antibodies against EGFR and assess their affinity to EGFR and anti-tumor cell migration effect. Methods:L and V_H genes of humanized antibodies against EGFR were designed and synthesized. Genes encoding V_H and C_H were connected and then cloned into a pIRES based bicistronic expression vector. Gene encoding the corresponding L gene was also cloned into the same vector. 293T cells were transfected with the recombinant plasmid and the antibody expression was confirmed by Western blotting. The antibodies were purified by protein A based affinity chromatography. Binding of the humanized antibody to the EGFR was assessed by Surface Plasmon Renainance with Biacore3000, and the biological activity of the humanized antibody was determined by tumor cell invasion test.Results:Three expression vectors were constructed and the humanized anti-EGFR antibodies were expressed and purified successfully. In reducing SDS-PAGE, the antibodies exhibited two bands of approximately 25×10~3and 50×10~3, respectively. Western blot assay showed that the humanized antibodies had recognition specificity to goat-human IgG antiserum. Biacore assay revealed that the humanized antibody C3 binds to EGFR with high affinity(6.13×10~(-10)M). Cell migration test showed that C2,C3 and C5 could suppress growth and migration of tumor cells.Conclusion:Three anti-EGFR humanized antibodies (C2,C3 and C5) have been constructed and expressed successfully, and the C3 antibody retained high affinity for EGFR and showed improved inhibitory effect on tumor cell growth and migration.

Study on relationship between length of homologous sequences and chromosomic recombination rate in Saccharopolyspora erythraea / 生物工程学报

In order to study the relationship between lengths of homologous fragments and chromsomic recombination rate in Saccharopolyspora erythraea, three homologous sequences, with mutant loci and different flanking sequences, (26bp + 27bp), (500bp + 576bp) and (1908bp + 1749bp), were synthesized by chemical reaction or PCR amplification, and cloned into pWHM3 to construct homologous recombination plasmids, pWHM1113, pWHM1116 and pWHM1119. When the plasmids were transformed into protoplast of Saccharopolyspora erythraea A226 under PEG mediated, on an average 30, 69 and 170 transformants grew on each plate for the three plasmids respectively, but chromosomic integration frequency were 0, 2% and 19% among corresponding transformants. Both pWHM1116 and pWHM1119 could take double crossover recombination, and exchange the mutant loci in the chromosome. It was concluded that when the flanking sequences were equal or more than (500bp + 576bp), they could take effective single and double recombination with Saccharopolyspora erythraea chromosome.

Construction of Saccharopolyspora erythraea M synthesizing a novel ketolide 3-deoxy-3-oxo-erythronolide B / 生物工程学报

Genetic engineering on macrolide antibiotics was a new field in recent years and more than 100 novel polyketides had been produced until then. Using genomic DNA of S. erythraea A226 as a template, about 3.2 kb DNA fragment without KR6 domain was amplified by overlapping PCR technique and cloned into pWHM3 carrier, which resulted in the construction of homologous recombinant plasmid pWHM2201. Plasmid pWHM2201 was introduced into protoplasts of S. erythraea A226 by PEG-mediated transformation and integrated into the gene locus for erythromycin biosynthesis. After integrants grew for two generations on R3M media without Tsr, they were protoplasted and grown on R3M plates. By PCR identification, 8 mutants without KR6 domain were selected out and named S. erythraea M(1-8). With the identification of mass spectrometry, it was proved that S. erythraea M1 synthesized a novel ketolide compound 3-deoxy-3-oxo-erythronolide B.