Potassium channels show a huge variability in the affinity when recognizing enormous bioactive peptides, and the elucidation of their recognition mechanism remains a great challenge due to an undetermined peptide-channel complex structure. Here, we employed combined computation methods to study the specific binding of BeKm-1 peptide to the hERG potassium channel, which is an essential determinant of the long-QT syndrome. By the use of a segment-assembly homology modeling method, the closed-state hERG structure containing unusual longer S5P linker was successfully constructed. It has a "petunia" shape, while four "petals" of symmetrically distributed S5P segments always decentralize. Starting from the hERG and BeKm-1 structures, a considerably reasonable BeKm-1-hERG complex structure was then screened out and identified by protein-protein docking, molecular dynamics (MD) simulations, and calculation of relative binding free energies. The validity of this predicted complex was further assessed by computational alanine-scanning, with the results correlating reasonably well with experimental data. In the novel complex structure, four considerably flexible S5P linkers are far from the BeKm-1 peptide. The BeKm-1 mainly uses its helical region to associate the channel outer vestibule, except for the S5P linker region; however, structural analysis further implies this neutral pore region with wiggling S5P linker is highly beneficial to the binding of BeKm-1 with lower positive charges. The most critical Lys18 of BeKm-1 plugs its side chain into the channel selectivity filter, while the secondarily important Arg20 forms three hydrogen bonds with spatially neighboring residues in the hERG channel. Different from the classical peptide-K+ channel interaction mainly induced by electrostatic interaction, a synergetic effect of the electrostatic and van der Waals interactions was found to mediate the molecular recognition between BeKm-1 and the hERG channel. And this specific binding process is revealed to be a dynamic change of reduction of binding free energy and conformational rearrangement mainly in the interface of both BeKm-1 and the hERG channel. All these structural and energy features yield deep insights on the high selective binding mechanism of hERG-specific peptides, present a diversity of peptide-K+ channel interactions, and also provide important clues to further study structure-function relationships of the hERG channel.

The misuse of antibiotics has led our age to a dangerous edge, as antibiotic-resistant pathogens appear to evolve more quickly than antibiotics are invented. Thus, new agents to treat bacterial infection are badly needed. Cationic host defense peptides are on the first line of a host defense system and are thought to be good candidates for treating bacterial infection. Here, a novel cationic host defense peptide, mucroporin, was cloned and characterized from the venom of Lychas mucronatus. The MIC for Staphylococcus aureus was 25 g/ml, including antibiotic-resistant pathogens. Based on the molecular template of mucroporin, mucroporin-M1 was designed by amino acid substitution. The MIC for S. aureus was 5 g/ml, including the antibiotic-resistant pathogens methicillin-resistant S. aureus, methicillin-resistant coagulase-negative Staphylococcus, penicillinresistant S. aureus, and penicillin-resistant S. epidermidis. Moreover, mucroporin-M1 also inhibited gramnegative bacteria. The modes of action of mucroporin and mucroporin-M1 were both rapid killing by disrupting the cell membrane of bacteria, and the number of surviving bacteria was reduced by about 4 to 5 orders of magnitude immediately after peptide delivery. These results showed that mucroporin could be considered a potential anti-infective drug, especially for treating antibiotic-resistant pathogens.

In natural ecosystems, endophytes, which live in the inner tissues of healthy plants, exhibit complex interactions with their hosts. During a long coevolutionary process with their hosts, endophytes have developed many significant and novel characteristics. In order to maintain a stable symbiosis, endophytes secrete varieties of extracellular enzymes that contribute to colonization and growth. All these specific enzymes, under certain conditions, could be exploited. Nowadays, more and more complex chemical reactions are being replaced by moderate and pollution-free enzymatic reactions. Bacteria have been widely used in bioengineering, but endophytes, as a kind of organism, have not been fully developed. Therefore, great efforts to develop endophyte resources could bring us a variety of benefits, such as novel and effective bioactive compounds that cannot be synthesized by chemical reactions. It is noteworthy that, after long-term coexistence with hosts, endophytes can synthesize biologically active substances similar to the secondary metabolites produced by host plants. This could help us to accumulate many valuable drug compounds such as paclitaxel and camptothecin in a short time period. In addition, endophytes are widespread in plant roots; they can deeply affect soil chemical composition, micro-ecosystems, and physical structure over their life cycle. Besides that, endophytes play an important role in the degradation of plant litter and organic pollutants, which have an active effect on the improvement of soil fertility. Endophytes are a most promising microbial resource, waiting to be exploited.

BackgroundJasmonic acid (JA) is a well-characterized signaling molecule in plant defense responses. However, its relationships with other signal molecules in secondary metabolite production induced by endophytic fungus are largely unknown. Atractylodes lancea (Asteraceae) is a traditional Chinese medicinal plant that produces antimicrobial volatiles oils. We incubated plantlets of A. lancea with the fungus Gilmaniella sp. AL12. to research how JA interacted with other signal molecules in volatile oil production.ResultsFungal inoculation increased JA generation and volatile oil accumulation. To investigate whether JA is required for volatile oil production, plantlets were treated with JA inhibitors ibuprofen (IBU) and nordihydroguaiaretic acid. The inhibitors suppressed both JA and volatile oil production, but fungal inoculation could still induce volatile oils. Plantlets were further treated with the nitric oxide (NO)-specific scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide potassium salt (cPTIO), the H2O2 inhibitors diphenylene iodonium (DPI) and catalase (CAT), and the salicylic acid (SA) biosynthesis inhibitors paclobutrazol and 2-aminoindan-2-phosphonic acid. With fungal inoculation, IBU did not inhibit NO production, and JA generation was significantly suppressed by cPTIO, showing that JA may act as a downstream signal of the NO pathway. Exogenous H2O2 could reverse the inhibitory effects of cPTIO on JA generation, indicating that NO mediates JA induction by the fungus through H2O2-dependent pathways. With fungal inoculation, the H2O2 scavenger DPI/CAT could inhibit JA generation, but IBU could not inhibit H2O2 production, implying that H2O2 directly mediated JA generation. Finally, JA generation was enhanced when SA production was suppressed, and vice versa.ConclusionsJasmonic acid acts as a downstream signaling molecule in NO- and H2O2-mediated volatile oil accumulation induced by endophytic fungus and has a complementary interaction with the SA signaling pathway.

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