From design to screening: a new antimicrobial peptide discovery pipeline.

Antimicrobial peptides (AMPs) belong to a class of natural microbicidal molecules that have been receiving great attention for their lower propensity for inducing drug resistance, hence, their potential as alternative drugs to conventional antibiotics. By generating AMP libraries, one can study a large number of candidates for their activities simultaneously in a timely manner. Here, we describe a novel methodology where in silico designed AMP-encoding oligonucleotide libraries are cloned and expressed in a cellular host for rapid screening of active molecules. The combination of parallel oligonucleotide synthesis with microbial expression systems not only offers complete flexibility for sequence design but also allows for economical construction of very large peptide libraries. An application of this approach to discovery of novel AMPs has been demonstrated by constructing and screening a custom library of twelve thousand plantaricin-423 mutants in Escherichia coli. Analysis of selected clones by both Sanger-sequencing and 454 high-throughput sequencing produced a significant amount of data for positionally important residues of plantaricin-423 responsible for antimicrobial activity and, moreover, resulted in identification of many novel variants with enhanced specific activities against Listeria innocua. This approach allows for generation of fully tailored peptide collections in a very cost effective way and will have countless applications from discovery of novel AMPs to gaining fundamental understanding of their biological function and characteristics.