Engineering Escherichia coli for l-homoserine production.

l-homoserine, a nonprotein amino acid, is used to synthesize many active substances in the industry. Here, to develop a robust l-homoserine-producing strain, Escherichia coli W3110 was used as a chassis to be engineered. Based on a previous construct with blocked competing routes for l-homoserine synthesis, five genes were overexpressed by promoter replacement strategy to increase the l-homoserine production, including enhancement of precursors for l-homoserine synthesis (ppc, thrA, and asd), reinforcement of the NADPH supply (pntAB) and efflux transporters (rhtA) to improve the l-homoserine production. However, the plasmid losing was to blame for the wildly fluctuating fermentation performance of engineered strains, ranging between 2.1 and 6.2 g/L. Then, a hok/sok toxin/antitoxin system was introduced into the free plasmid expression cassette to maintain the genetic stability of the episomal plasmid; consequently, the plasmid-losing rate sharply decreased, resulting in the engineered strain SHL17, which exhibited excellent stability in l-homoserine production, with 6.3 g/L in shake flasks and 44.4 g/L in a 5-L fermenter without antibiotic addition. This work verified the effective use of the hok/sok toxin/antitoxin system combined with promoter engineering to improve the genetic stability of E. coli episomal plasmids without antibiotics.

Structure-guided engineering of a flavin-containing monooxygenase for the efficient production of indirubin.

Indirubin is a bisindole compound for the treatment of chronic myelocytic leukemia. Here, we presented a structure-guided method to improve the activity of a flavin-containing monooxygenase (bFMO) for the efficient production of indirubin in Escherichia coli. A flexible loop interlocked with the active pocket through a helix and the substrate tunnel rather than the active pocket in bFMO were identified to be two reconfigurable structures to improve its activity, resulting in K223R and N291T mutants with enhanced catalytic activity by 2.5- and 2.0-fold, respectively. A combined modification at the two regions (K223R/D317S) achieved a 6.6-fold improvement in catalytic efficiency (kcat/Km) due to enhancing π-π stacking interactions stabilization. Finally, an engineered E. coli strain was constructed by metabolic engineering, which could produce 860.7 mg/L (18 mg/L/h) indirubin, the highest yield ever reported. This work provides new insight into the redesign of FMOs to boost their activities and an efficient approach to produce indirubin.

Interleukin-12 receptor ß2 from grass carp: Molecular characterization and its involvement in Aeromonas hydrophila-induced intestinal inflammation.

Interleukin-12 receptor ß2 (IL-12Rß2) is a signaling subunit of heterodimeric receptors for IL-12 and IL-35. It plays important regulatory functions in the development of Th1 cells and in the expression of inflammatory cytokines in mammals and other higher vertebrates. However, little is known about IL-12Rß2 in teleost fish. In this work, we have cloned and characterized IL-12Rß2 from grass carp (Ctenopharyngodon idella). The full-length cDNA of grass carp IL-12Rß2 is 2875 bp, which encodes a mature protein with 741 amino acids. This mature protein contains three fibronectin type III domains, a transmembrane helix, and CXW and WSXWS-like motifs that are characteristic of the type I cytokine receptor family. Phylogenetic analysis revealed that cyprinid fish IL-12Rß2 formed a single branch, clearly separated from those of other vertebrates. We expressed and purified a recombinant grass carp IL-12Rß2 protein containing major antigenic regions, which was used to raise a polyclonal antibody. The specificity of the antibody was assessed by Western blotting analysis of whole cell lysates from Escherichia coli cells expressing the recombinant IL-12Rß2, grass carp intestinal intraepithelial lymphocytes, and cultured C. idella kidney cells. To explore the potential regulatory role of IL-12Rß2 in inflammation, we generated an intestinal inflammation model by anal intubation of fish with Aeromonas hydrophila. Immunohistochemical staining of the inflamed intestines revealed that IL-12Rß2 expression is consistent with inflammatory cell recruitment during intestinal inflammation. Real-time quantitative PCR revealed that IL-12Rß2 is widely expressed in normal tissues and is up-regulated in most tissues after infecting with A. hydrophila. We found that IL-12Rß2, IL-12p35, and interferon-γ were expressed in similar patterns in the intestines during inflammation. Taken together, our results suggest that IL-12Rß2 is involved in the regulation of intestinal inflammation.

Characterization of interleukin-1ß as a proinflammatory cytokine in grass carp (Ctenopharyngodon idella).

Interleukin-1ß (IL-1ß) is a well-characterized cytokine that plays key roles in cellular responses to infection, inflammation, and immunological challenges in mammals. In this study, we identified and analyzed a grass carp (Ctenopharyngodon idella) ortholog of IL-1ß (gcIL-1ß), examined its expression patterns in various tissues in both healthy and lipopolysaccharide (LPS)-stimulated specimens, and evaluated its proinflammatory activities. The gcIL-1ß gene consists of seven exons and six introns. The full-length cDNA sequence contains an open reading frame of 813 nucleotides. The deduced amino acid sequence exhibits a characteristic IL-1 signature but lacks the typical IL-1ß converting enzyme cleavage site that is conserved in mammals. In the phylogenetic tree, IL-1ßs from grass carp and other members of the Cyprinidae family clustered into a single group. Expression pattern analysis revealed that gcIL-1ß is constitutively expressed in all 11 tissues examined, and LPS stimulation leads to significant up-regulation in muscle, liver, intestine, skin, trunk kidney, head kidney, and gill. Recombinant grass carp IL-1ß (rgcIL-1ß) was generated prokaryotically as a fusion protein of Trx-rgcIL-1ß. An anti-rgcIL-1ß polyclonal antibody (rgcIL-1ß pAb) was raised in mice against the purified Trx-rgcIL-1ß. Western blot analysis confirmed that rgcIL-1ß pAb reacted specifically with gcIL-1ß in C. idella kidney (CIK) cells. Quantitative real-time PCR data indicated that intestinal mRNA expression levels of endogenous IL-1ß, IL-1R2, and TNF-α were significantly up-regulated following Trx-rgcIL-1ß exposure. The inhibitory activities of rgcIL-1ß pAb against the inflammatory response were confirmed in a model of Aeromonas hydrophila-induced intestinal inflammation. Our immunohistochemical study revealed that the degree and intensity of inflammatory cell infiltration are fully consistent with the observed mRNA expression patterns of these key inflammatory genes. Taken together, these data suggest that gcIL-1ß plays a critical role in the proinflammatory response in the grass carp intestine.

[Amplification of Ds flanking sequences from rice genomic DNA of hybrids of Ac x Ds lines and the analysis of Ds insertions].

Ac and Ds insertions among the genomic DNAs of hybrids of Ac x Ds lines were screened by PCR. The genomic DNAs, which were proved to harbour both Ac and Ds, were used as templates in TAIL-PCR to clone the Ds flanking sequences. The cloned specific fragments were sequenced, and the sequenced Ds flanking sequences were used as query sequences to perform on-line sequence comparing analysis against GenBank by employing BLAST program of NCBI. The information about the chromosome location of Ds-inserted genes, or genes immediately downstream of the inserted sites, and their functional innotations were achieved. Based on the analysis from the cloned 93 Ds-flanking sequences, it was found that 21 hybrid plants had Ds insertions in genic regions, whereas the remaining 72 samples's intergenic regions were inserted by Ds element. Moreover, among the 72 regions, 12 were inserted immediately upstream (within 3 kb) of specific genes. Also, the strategies to improve the performance in cloning the Ds flanking sequences and in screening the Ac/Ds lines were emphasized.

[cDNA cloning and sequence analysis of leginsulin gene in broad bean (Vicia faba)].

In order to elucidate the relationship between the structural features of leginsulin gene in legume plants and their phylogenetic significance, we have cloned the cDNA sequence of leginsulin gene from radicles of broad bean (Vicia faba) via RT-PCR techniques according to the leginsulin gene sequence we previously obtained from soybean (Glycine max). The cloned cDNA encoded for a precursor protein consisting of the signal peptide, mature leginsulin and an additional 45 amino acids of another polypeptide. A sequence search for homology comparison revealed the cloned leginsulin cDNA fragment shares 62.5% and 58.7% similarity to soybean and pea, respectively. The results also shown that leginsulin cDNA from broad bean presents 44.2% and 43.6% amino acid sequence homology with soybean and pea (Pisum sativum), respectively, and that there exists highly conserved cysteine sites among the leginsulin cDNAs, which may play a crucial role in maintaining the three-dimensional structure and the physiological functions of leginsulin.