Difference between revisions of "Part:BBa K1919000"

Revision as of 16:07, 11 October 2016

The coding sequence of antimicrobial peptide CecropinXJ

Antimicrobial peptide CecropinXJ belongs to AMP family Cecropin, a group of small basic polypeptides mainly found in the hemolymph of insects, consist of 31-39 amino acid residues and have a broad spectrum, high heat stability and potent bacteriostatic activity.

Sequence and Features

Biology

Antimicrobial peptides (AMPs) are a group of peptides that play roles in the innate immune system to protect the host from invading pathogens [1]. AMPs have minimal toxicity and low sensitivity effects to the host [2], which means antimicrobial peptides have the potential to be used to replace antibiotics in the future. Thus, the detrimental effects of antibiotics overuse will be released.

Cecropins, a group of small AMPs mainly found in the hemolymph of insects, consist of 31 39 amino acid residues and have a broad spectrum, high heat stability and potent bacteriostatic activity [3-5]. CecropinXJ (Part BBa_K1919000) is a member of the Cecropin family, which was first cloned from the larvae of the Xinjiang silkworm (Bombyx mori). Previous researches have determined the complete amino acid sequence of this molecule [6]. It has been demonstrated that CecropinXJ could be expressed in eukaryotic expression system such as Pichia pastoris [7] or prokaryotic expression system such as E.coli [8]. What’s more, CecropinXJ exhibited to have various activities such as antibacterial activity against both Gram‑positive and Gram-negative bacteria, as well as antifungal activity [8]. These characteristics indicate that CecropinXJ is an ideal antimicrobial substance to be used to treat foot diseases caused by microbes.

Results

Considering the fact that an antimicrobial peptide expressed in bacteria may be cytotoxic to the host or subjected to degradation by host-derived peptidases [9,10], we used the recombinant expression system to overcome the potential problems ——fusing the DNA coding sequence of CecropinXJ with the sequence of a bacterial thioredoxin gene exists in the pET32a(+) expression system [3,4]. To construct recombinant pET32a-cecropinXJ expression vector (Fig.1B), we used artificially synthetic CecropinXJ synthesized by Tsingke Ltd. (Fig.1A). Subsequently, CecropinXJ and pET32a plasmid were subjected to enzymatic digestion with EcoRI and XhoI, and ligated using T4 DNA ligase.

Fig.1A Schematic structure of CecropinXJ in pSB1C3

Fig.1B Schematic structure of CecropinXJ in pET32a(+)

After that, we selected positive clones which were resistant to ampicillin on LB plate to confirm the plasmid through PCR and DNA sequencing. The verified recombinant plasmid was transformed into the E. coli strain BL21(DE3) pLYsS competent cells [8], which encodes a chromosomal T7 RNA polymerase under the control of a tac promoter.

When the optical density at OD600nm of the culture reached 0.6-0.8, we added 0.8mM IPTG to induce the cells, by which time the tac promoter was activated and drove expression of pET32a-CecropinXJ. After 5 hours induction at 37 ̊C, the expression level of recombinant CecropinXJ was detected through SDS-PAGE and western blot analysis. In the result of SDS-PAGE (Fig.3), an obvious band at the size of 25 kDa compared with control was observed, which was as expected. The result of western blot analysis provided subsequent confirmation of expression (Fig.4).

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