Infectious diseases are among the leading global causes of death, increasing the search for novel antibacterial agents. Among these, biologically active peptides are an excellent research tool. Using solid-phase peptide synthesis (SPPS), this work aimed to synthesize the peptide derived from the C-terminal region of Bothropstoxin-I (BthTX-I) (p-BthTX-I, sequence: KKYRYHLKPFCKK), and its disulfide-linked dimeric form, obtained via air oxidation (p-BthTX-I)2. Two other peptides were synthesized to evaluate the dimerization effect on antimicrobial activity. In both sequences, the cysteine (Cys) residue was replaced by the serine (Ser) residue, differing, however, in their C-terminus position. The antimicrobial activity of the peptides against gram-negative (Escherichia (E.) coli) and gram-positive (Staphylococcus (S.) aureus) bacteria and yeast (Candida (C.) albicans) was evaluated. Interestingly, only peptides containing the Cys residue showed antimicrobial activity, suggesting the importance of Cys residue and its dimerization for the observed activity. Apparently, p-BthTX-I and (p-BthTX-I)2 did not promote lysis or form pores and were not able to interact with membranes. Furthermore, they neither showed antifungal activity against C. albicans nor toxicity against erythrocytes, epithelial cells, or macrophages, indicating a potential specificity against prokaryotic cells.

Electrochemical immunosensors offer much in the potential translation of a lab based sensing capability to a useful "real world" platform. In previous work we have introduced an impedance-derived electrochemical capacitance spectroscopic analysis as supportive of a reagentless means of reporting on analyte target capture at suitably prepared mixed-component redox-active, antibody-modified interfaces. Herein we directly integrate receptive aptamers into a redox charging peptide support in enabling a label-free low picomolar analytical assay for C-reactive protein with a sensitivity that significantly exceeds that attainable with an analogous antibody interface.

Antimicrobial peptides can be used systemically, however, their susceptibility to proteases is a major obstacle in peptide-based therapeutic development. In the present study, the serum stability of p-BthTX-I (KKYRYHLKPFCKK) and (p-BthTX-I)2, a p-BthTX-I disulfide-linked dimer, were analyzed by mass spectrometry and analytical high-performance liquid chromatography (HPLC). Antimicrobial activities were assessed by determining their minimum inhibitory concentrations (MIC) using cation-adjusted Mueller–Hinton broth. Furthermore, biofilm eradication and time-kill kinetics were performed. Our results showed that p-BthTX-I and (p-BthTX-I)2 were completely degraded after 25 min. Mass spectrometry showed that the primary degradation product was a peptide that had lost four lysine residues on its C-terminus region (des-Lys12/Lys13-(p-BthTX-I)2), which was stable after 24 h of incubation. The antibacterial activities of the peptides p-BthTX-I, (p-BthTX-I)2, and des-Lys12/Lys13-(p-BthTX-I)2 were evaluated against a variety of bacteria, including multidrug-resistant strains. Des-Lys12/Lys13-(p-BthTX-I)2 and (p-BthTX-I)2 degraded Staphylococcus epidermidis biofilms. Additionally, both the peptides exhibited bactericidal activities against planktonic S. epidermidis in time-kill assays. The emergence of bacterial resistance to a variety of antibiotics used in clinics is the ultimate challenge for microbial infection control. Therefore, our results demonstrated that both peptides analyzed and the product of proteolysis obtained from (p-BthTX-I)2 are promising prototypes as novel drugs to treat multidrug-resistant bacterial infections.

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Antimicrobial resistance is a global health problem with strong social and economic impacts. The development of new antimicrobial agents is considered an urgent challenge. In this regard, Antimicrobial Peptides (AMPs) appear to be novel candidates to overcome this problem. The mechanism of action of AMPs involves intracellular targets and membrane disruption. Although the exact mechanism of action of AMPs remains controversial, most AMPs act through membrane disruption of the target cell. Several strategies have been used to improve AMP activity, such as peptide dimerization. In this review, we focus on AMP dimerization, showing many examples of dimerized peptides and their effects on biological activity. Although more studies are necessary to elucidate the relationship between peptide properties and the dimerization effect on antimicrobial activity, dimerization constitutes a promising strategy to improve the effectiveness of AMPs.