Lf-CATH2

LL-37 is the only cathelicidin-derived antimicrobial peptide found in humans and it has a multifunctional role in host defense. The peptide has been shown to possess immunomodulatory functions in addition to antimicrobial activity. To provide sufficient material for biological and structural characterization of this important peptide, various systems were developed to produce recombinant LL-37 in Escherichia coli. In one previous approach, LL-37 coding sequence was cloned into vector pET-32a, allowing the peptide to be expressed as a thioredoxin fusion. The fusion protein contains two thrombin cleavage sites: a vector-encoded one that is 30-residue upstream of the insert and an engineered one that is immediately adjacent to LL-37. Cleavage at these two sites shall generate three fragments, one of which is the target peptide. However, when the fusion protein was treated with thrombin, cleavage only occurred at the remote upstream site. A plausible explanation is that the thrombin site adjacent to LL-37 is less accessible due to the peptide's aggregation tendency and cleavage at the remote site generates a fragment, which forms a large aggregate that buries the intended site. In this study, I deleted the vector-encoded thrombin site and S tag in pET-32a, and then inserted the coding sequence for LL-37 plus a thrombin site into the modified vector. Although removing the S tag did not change the oligomeric state of the fusion protein, deletion of the vector-encoded thrombin site allowed the fusion to be cleaved at the engineered site to release LL-37. The released peptide was separated from the carrier and cleavage enzyme by size-exclusion chromatography. This new approach enables a quick production of high quality active LL-37 with a decent amount.

Objective: To construct human apolipoprotein O (apolipoprotein O, ApoO) expression vector and obtain recombinant fusion protein thioredoxin (Trx)-ApoO by pET prokaryotic expression system. Methods: The ApoO gene fragment from the human liver cDNA library was amplified by PCR. The resulting product was cloned into pET-32a(+) vector and sequenced. The confirmed cDNA was cloned into plasmid E.coli DH10B and then transformed into E.coli BL 21 (DE3) where it was induced to express protein by isopropyl β-D-1-thiogalactopyranoside (IPTG). The fusion protein was purified by Ni-NTA resin. Results: The ApoO gene was cloned by PCR and a 519 bp DNA fragment was shown on the agarose electrophoresis. The cloned gene was sequenced and demonstrated to have the same sequence as that of human ApoO gene in GenBank which justified a successful construction of recombinant plasmid. ApoO cDNA gene fragment was induced by IPTG, and a 34 kD recombinant fusion protein Trx-ApoO was tested on sodium dodecyl sulfate polyacrylamide (SDS-PAGE). Conclusion: Human ApoO gene is successfully cloned and its recombinant fusion protein Trx-ApoO is expressed.

LL-37 is a human antimicrobial peptide that has been shown to possess multiple functions in host defense. In this report, the peptide was expressed as a fusion with a thioredoxin-SUMO dual-tag. Upon SUMO protease mediated cleavage at the SUMO/peptide junction, LL-37 with its native N-terminus was generated. The released peptide was separated from the dual-tag and cleavage enzyme by size-exclusion chromatography. Mass spectrometry analysis proves that the recombinant peptide has a molecular weight as theoretically expected for its native form. The produced peptide displayed antimicrobial activity against Escherichia coli K-12. On average, 2.4 mg peptide was obtained from one liter of bacterial culture. Thus, the described approach provides an effective alternative for producing active recombinant LL-37 with its natural amino acid sequence in E. coli.