Profiling the linear peptides of venom from the Brazilian scorpion Tityus serrulatus: structural and functional characterization

Scorpion venoms are a rich source of bioactive peptides, most of which are neurotoxic, with 30 to 70 amino acid residues in their sequences. There are a scarcity of reports in the literature concerning the short linear peptides found in scorpion venoms. This type of peptide toxin may be selectively extracted from the venom using 50% (v/v) acetonitrile. The use of LC-MS and MS/MS enabled the detection of 12 bioactive short linear peptides, of which six were identified as cryptides. These peptides were shown to be multifunctional, causing hemolysis, mast cell degranulation and lysis, edema, pain, and anxiety, increasing the complexity of the envenomation mechanism. Apparently, the natural functions of these peptide toxins are to induce inflammation and discomfort in the victims of scorpion stings.

Structure-activity relationship of mastoparan analogs: Effects of the number and positioning of Lys residues on secondary structure, interaction with membrane-mimetic systems and biological activity.

In this study, a series of mastoparan analogs were engineered based on the strategies of Ala and Lys scanning in relation to the sequences of classical mastoparans. Ten analog mastoparans, presenting from zero to six Lys residues in their sequences were synthesized and assayed for some typical biological activities for this group of peptide: mast cell degranulation, hemolysis, and antibiosis. In relation to mast cell degranulation, the apparent structural requirement to optimize this activity was the existence of one or two Lys residues at positions 8 and/or 9. In relation to hemolysis, one structural feature that strongly correlated with the potency of this activity was the number of amino acid residues from the C-terminus of each peptide continuously embedded into the zwitterionic membrane of erythrocytes-mimicking liposomes, probably due to the contribution of this structural feature to the membrane perturbation. The antibiotic activity of mastoparan analogs was directly dependent on the apparent extension of their hydrophilic surface, i.e., their molecules must have from four to six Lys residues between positions 4 and 11 of the peptide chain to achieve activities comparable to or higher than the reference antibiotic compounds. The optimization of the antibacterial activity of the mastoparans must consider Lys residues at the positions 4, 5, 7, 8, 9, and 11 of the tetradecapeptide chain, with the other positions occupied by hydrophobic residues, and with the C-terminal residue in the amidated form. These requirements resulted in highly active AMPs with greatly reduced (or no) hemolytic and mast cell degranulating activities.

Combining experimental evidence and molecular dynamic simulations to understand the mechanism of action of the antimicrobial octapeptide jelleine-I.

Jelleines are four naturally occurring peptides that comprise approximately eight or nine C-terminal residues in the sequence of the major royal jelly protein 1 precursor (Apis mellifera). The difference between these peptides is limited to one residue in the sequence, but this residue has a significant impact in their efficacy as antimicrobials. In peptide-bilayer experiments, we demonstrated that the lytic, pore-forming activity of Jelleine-I is similar to that of other cationic antimicrobial peptides, which exhibit stronger activity on anionic bilayers. Results from molecular dynamics simulations suggested that the presence of a proline residue at the first position is the underlying reason for the higher efficacy of Jelleine-I compared with the other jelleines. Additionally, simulations suggested that Jelleine-I tends to form aggregates in water and in the presence of mimetic membrane environments. Combined experimental evidence and simulations showed that the protonation of the histidine residue potentiates the interaction with anionic palmitoyl-oleoyl-phosphatidylcholine/palmitoyl-oleoyl-phosphatidylglycerol (POPC/POPG) (70:30) bilayers and reduces the free energy barrier for water passage. The interaction is driven by electrostatic interactions with the headgroup region of the bilayer with some disturbance of the acyl chain region. Our findings point to a mechanism of action by which aggregated Jelleine-I accumulates on the headgroup region of the membrane. Remaining in this form, Jelleine-I could exert pressure to accommodate its polar and nonpolar residues on the amphiphilic environment of the membrane. This pressure could open pores or defects, could disturb the bilayer continuity, and leakage would be observed. The agreement between experimental data and simulations in mimetic membranes suggests that this approach may be a valuable tool to the understanding of the molecular mechanisms of action.