Antimicrobial peptides have received increasing attention as a new pharmaceutical substance, because of their broad spectrum of antimicrobial activities and the rapid development of multidrug- resistant pathogenic microorganisms. The main obstacle to the wide application of antimicrobial peptides has been the lack of a cost-effective, mass-production method. A system was developed for the efficient expression of antimicrobial peptides in Escherichia coli as tandem repeats.
Various-sized multimers of a gene encoding an antimicrobial peptide, magainin, were obtained with the gene amplification vector, pBBS1: larger multimers, up to about 108 copies, were constructed from the monomer by the sequential amplification procedure. The multimers were the most stable in E. coli D1210 among E. coli hosts examined for the stability of multimers.
A mass-production method for an antimicrobial peptide, buforin II, has been developed by fusing the antimicrobial peptide to an acidic peptide. Multimers of the acidic peptide-buforin II fusion protein were expressed at the very high level without causing damage to the cells. The presence of cysteine residues in the acidic peptide enhanced the expression level substantially by facilitating the interaction of the negatively charged acidic peptide and positively charged buforin II through aggregate formation in tandem repeats, thereby effectively neutralizing the positive charge of buforin II. Multimers of this fusion protein were expressed as inclusion bodies, and more than 100 mg of pure buforin II was obtained from 1 L of E. coli culture by cleaving the multimers with CNBr. Recombinant buforin II had an antimicrobial activity identical to that of natural buforin II.
Other approaches have been tried to further increase the expression of buforin II fused to the acidic peptide as tandem repeats by stabilization of long mRNA transcripts or more efficient neutralization of positive charges of buforin II through disulfide bond format...