Tian et al. BMC Genomics 2010, 11:187 http://www.biomedcentral.com/1471-2164/11/187 Page 6 of 19 Figure 3 Navitricins. A. Sequence alignment of navitricins with fungal DLPs. The position of a phase 1 intron is boxed in red; B. The model structure of navitricin-1. Its fourth bridge, which links the n-loop to c-loop, is indicated by arrows. Ac: Aspergillus clavatus, Af: A. fumigatus, Nf: Neosartorya fischeri, Cg: Chaetomium globosum, Ao: A. oryzae, Afl: A. flavus. sequence identity (50%) with A. mellifera abaecin. To understand how nabaecins extended their carboxyl-ter- mini, we further searched the N. vitripennis database and found that a peptide (named navitripenicin) pos- sesses highly identical amino acid sequence to the car- boxyl-termini of nabaecins (herein named C-terminal navitripenicin unit, CtNU), but the region corresponding to abaecin is replaced by an acidic propeptide with a dibasic cleavage site. High content of glycines together with positively charged characteristics suggest that CtNU and navitripenicin belong to putative AMPs. A conserved phase 0 intron located at a nearly identical position among all these peptides (Figure 5) supports their evolutionary relatedness. (2) Hymenoptaecin Hymenoptaecin is an antibacterial peptide rich in glycine, which was identified only in Hymenopteran insects [56,59,60]. The mature hymenop- taecin is released by cleaving off a signal peptide and an acidic propeptide after bacterial infection. Expression of the hymenoptaecin gene was also regulated by the IMD pathway [57]. It inhibits the viability of Gram-negative and Gram-positive bacteria, including several human pathogens [56]. Similarity search of the N. vitripennis genome identified two hymenoptaecin-like peptides (named nahymenoptaecin-1 and nahymenoptaecin-2) with a unique amino-terminal AMP-like region corre- sponding to the propeptide of bee hymenoptaecins in position (Figure 6A). Functional characterization and evolutionary significance of nahymenoptaecin-1 has been described recently [26]. Nahymenoptaecin-2 presents a more interesting struc- tural feature in the mature peptide region, whose amino- and carboxyl-termini are respectively a Pro-rich peptide (named pronavicin) and a hymenoptaecin-like peptide with four internal repeats. Overall, these repeats can be well aligned with hymenoptaecin except a