Identification of a novel Plasmopara halstedii elicitor protein combining de novo peptide sequencing algorithms and RACE-PCR

Novel Antifungal Peptides Produced by Leuconostoc mesenteroides DU15 Effectively Inhibit Growth of Aspergillus niger

The ability of Leuconostoc mesenteroides DU15 to produce antifungal peptides that inhibit growth of Aspergillus niger was evaluated under optimum growth conditions of 30 °C for 48 h. The cell-free supernatant showed inhibitory activity against A. niger. Five novel peptides were isolated with the sequences GPFPL, YVPLF, LLHGVPLP, GPFPLEMTLGPT, and TVYPFPGPL as identified by de novo sequencing using PEAKS 6 software. Peptide LLHGVPLP was the only positively charged (cationic peptides) and peptide GPFPLEMTLGPT negatively charged (anionic), whereas the rest are neutral. The identified peptides had high hydrophobicity ratio and low molecular weights with amino acids sequences ranging from 5 to 12 residues. The mode of action of these peptides is observed under the scanning electron microscope and is due to cell lysis of fungi. This work reveals the potential of peptides from L. mesenteroides DU15 as natural antifungal preservatives in inhibiting the growth of A. niger that is implicated to the spoilage during storage.

De novo sequencing and homology searching

In proteomics, de novo sequencing is the process of deriving peptide sequences from tandem mass spectra without the assistance of a sequence database. Such analyses have traditionally been performed manually by human experts, and more recently by computer programs that have been developed because of the need for higher throughput. Although powerful, de novo sequencing often can only determine partially correct sequence tags because of imperfect tandem mass spectra. However, these sequence tags can then be searched in a sequence database to identify the exact or a homologous peptide. Homology searches are particularly useful for the study of organisms whose genomes have not been sequenced. This tutorial will present background important to understanding de novo sequencing, suggestions on how to do this manually, plus descriptions of computer algorithms used to automate this process and to subsequently carryout homology-based database searches. This Tutorial is part of the International Proteomics Tutorial Programme (IPTP 1).