Palustrin-OG1 antimicrobial peptide

OG2 is a modified antimicrobial peptide of Palustrin-OG1 (OG1), which is derived from Odorrana grahami frog. OG2 has shown much higher selective antimicrobial activity and lower hemolytic activity than OG1, indicating OG2 may be a promising antimicrobial agent. In this study, we investigated three fusion partners, including thioredoxin, Mxe GyrA intein, and small ubiquitin-like modifier (SUMO), each fused with OG2, and examined their effects on the expression level and solubility of OG2 in Escherichia coli. The codon-optimized OG2 gene was cloned into pET32a (+) and pTWIN1 for fusion with thioredoxin and Mxe GyrA intein, respectively. In addition, the SUMO-OG2 gene was amplified by splice overlap extension PCR method and was cloned into pET30a (+). All recombinant plasmids were then transformed into E. coli BL21(DE3)pLysS, and the expressed fusion proteins were verified. Upon isopropyl β-D-1-thiogalactopyranoside (IPTG) induction, OG2 fused with thioredoxin (Trx-OG2) showed the highest yield as a soluble fusion protein (50 mg/L), followed by Mxe GyrA intein (44 mg/L) and SUMO (11 mg/L). The thioredoxin-fused protein (Trx-OG2) was then purified by nickel-nitrilotriacetic acid chromatography and desalted by Sephadex G25. The OG2 released by both tobacco etch virus protease and enterokinase from Trx-OG2 showed strong antimicrobial activity against Staphylococcus aureus ATCC25923.

Palustrin-OG1 (OG1) is a host defense peptide isolated from the frog Odorrana grahami. In this study, we analyzed the chemical properties, antimicrobial activities and cytotoxicities of OG1 and its derivatives to identify the most promising peptide as an antimicrobial agent. By increasing the net positive charge, amphipathicity and decreasing the mean hydrophobicity of OG1, the derivative named as OG2 exerted higher antimicrobial activity against bacteria but lower cytotoxicity against both porcine erythrocytes and peripheral blood mononuclear cells than did OG1 (P<0.01). After substitution of Cys residues of OG2 by Ala or Trp residues, two derivatives named as OG2A and OG2W were less effective against bacteria and induced greater hemolysis than did OG2, indicating the importance of Cys residues. The substitution of the C-terminal Thr of OG2 resulted OG2N, which decreased the cytotoxicity and improved killing kinetics against gram-positive bacteria by the rapid damage of cell wall and membrane.

OG2 is a modified antimicrobial peptide, that is, derived from the frog peptide Palustrin-OG1. It has high antimicrobial activity and low cytotoxicity, and it is therefore promising as a therapeutic agent. Both prokaryotic (Escherichia coli) and eukaryotic (Pichia pastoris) production host systems were used to produce OG2 in our previous study; however, it was difficult to achieve high expression yields and efficient purification. In this study, we achieved high-yield OG2 expression using the intein fusion system. The optimized OG2 gene was cloned into the pTWIN1 vector to generate pTWIN-OG2-intein2 (C-terminal fusion vector) and pTWIN-intein1-OG2 (N-terminal fusion vector). Nearly 70% of the expressed OG2-intein2 was soluble after the IPTG concentration and induction temperature were decreased, whereas only 42% of the expressed of intein1-OG2 was soluble. Up to 75 mg of OG2-intein2 was obtained from a 1l culture, and 85% of the protein was cleaved by 100 mM DTT. Intein1-OG2 was less amenable to cleavage due to the inhibition of cleavage by the N-terminal amino acid of OG2. The purified OG2 exhibited strong antimicrobial activity against E. coli K88. The intein system is the best currently available system for the cost-effective production of OG2.