Sarah Tolentino Rocha Brandão

Background: Peptides are promising tools in medicine for viral, bacterial, and parasitic infections. MAP1 and MAP2 are peptides with antimicrobial activity. Aiming to increase selectivity, enhance antimicrobial activity, and reduce its cytotoxicity, two bioconjugates (GVL1-MAP2 and GVL1-MAP1) with the guanidine derivative group in the N-terminus position were synthesized. Methods: The peptides and bioconjugates were synthesized by SPPS. The biological activity and inhibition of the CPB enzyme were evaluated. Results: Antileishmanial activity was evaluated, and the bioconjugates exhibited higher activity in both the promastigote and amastigote forms than isolated GVL1 and peptides alone. Discussion: GVL1-MAP2 bioconjugate demonstrated not only the greatest activity against L. amazonensis in the promastigote (IC₅₀ = 3.2 μM) and amastigote (IC₅₀ = 0.6 μM) forms but also prevented the parasite from infecting new host cells, reducing the infection rate by 3-fold compared to the untreated control. Similar results were obtained in L. infantum, with IC₅₀ = 2.5 and 1.0 μM for promastigote and amastigote forms, respectively. In active serum, GVL1-MAP2 continued to show high activity. GVL1-MAP2 also showed bactericidal activity against most strains tested. The bioconjugate GVL1-MAP2 showed lower cytotoxicity than GVL1-MAP1 and amphotericin B in macrophages. Permeabilization studies and enzyme inhibition revealed that the peptide acts via at least two distinct mechanisms, with the primary mechanism targeting the membrane and inner targets as an inhibitor of the CPB enzyme. Conclusions: These data demonstrated that the synthesis of bioconjugates can be a tool for the development of bactericidal and antileishmanial compounds with improved potency and selectivity.

Redox-active moieties assembled on metallic interfaces have been shown to follow quantum mechanical rules, where the quantum capacitance of the interface (directly associated with the electronic structure of the redox-active moieties) plays a key role in the electron transfer dynamics of the interface. Modifying these interfaces with biological receptors has significant advantages (simplifying molecular diagnostics methods, reducing size, time, and cost while maintaining high sensitivity), enabling the fabrication of miniaturized electroanalytical devices that can compete with traditional ELISA and RT-PCR benchtop assay methods. Owing to their intrinsic characteristics, the use of peptide-based redox-active moieties is a promising chemical route for modifying metallic surfaces, resulting in a high quantum capacitive signal sensitivity. In the present work, different ferrocene-tagged peptides with a structure of Fc-Glu-XX-XX-Cys-NH₂ (XX = serine, phenylalanine, glycine) were used to form self-assembled monolayers on gold. The feasibility of using these interfaces in an electroanalytical assay was verified by detecting the NS1 DENV (Dengue Virus) biomarker to compare the efficiency of peptide structures for biosensing purposes. Parameters such as the formal potential of the interface, normalized electronic density of states (DOS), quantum capacitance, and electron transfer rate constants were obtained for Ser-, Phe-, and Gly-peptides. The Gly-peptide structure presented the highest analytical performance for sensing NS1 with a sensitivity of 5.6% per decade and the lowest LOD (1.4 ng mL^-1) and LOQ (2.6 ng mL^-1), followed by Phe-peptide, whereas Ser-peptide had the lowest performance. This work demonstrates that the use of peptides to fabricate a self-assembled monolayer as a biosensor component has advantages for low-cost point-of-care diagnostics. It also shows that the performance of the sensing interface depends strongly on how the chemistry of the surface is designed as a whole, not only on the redox-active group.