The principal molecular pathways of antimicrobial molecules involve the impairment of protein, lipid, cell wall, genetic material synthesis, and membrane injury (24). Cationic amphiphilic peptides primarily exert their action mechanism through membrane interaction and disruption (25, 26). This occurs due to their physicochemical properties; the positively charged peptide is attracted to the negatively charged bacterial plasma membrane (27). Subsequently, its amphiphilic characteristics enable the peptide to embed into the bacterial membrane, forming toroidal pores, barrel-stave pores, or carpet-like structures, leading to electrolytic imbalance and ultimately cell death (28–30). However, this mechanism is not specific, and cationic peptides are potentially cytotoxic (31).
However, some peptides interact with intracellular targets, inhibiting protein (e.g., Pleurocidin, Apidaecin Hb1a), lipid (e.g., Mersacidin, MBI-28), and DNA (e.g., Buforin II, Ostricacin-1) biosynthesis, thereby harming microbial development (24). The Heliquest results showed that Oligoventin is a neutral and hydrophilic peptide. Furthermore, experimental assays demonstrated that this peptide does not exhibit cytotoxicity against fresh human blood cells at a concentration of 500µM (32). Both results suggest that the antimicrobial activity of Oligoventin is associated with intracellular pathways, interfering with bacterial homeostasis.
PharmMapper is an online reverse docking tool that identifies targets using a mapping approach. After conducting the necessary methodology, 22 potential receptors for Oligoventin originating from both Gram-positive and Gram-negative microorganisms were identified. Subsequently, molecular docking was performed using PatchDock, revealing the best targets as thymidylate synthase ThyX (Idpdb 1O28), pyridoxine 5-phosphate synthase (Idpdb 1M5W), threonine dehydratase biosynthetic (Idpdb 1TDJ), enoyl-ACP reductase (Idpdb 1LXC), fumarate reductase flavoprotein subunit (Idpdb 1KSS), and cyclomaltodextrin glucanotransferase (Idpdb 1UKQ).
Moreover, only receptors 1LXC and 1TDJ exhibited negative ACE values, suggesting thermodynamically favorable interactions between Oligoventin and these receptors (33, 34). Notably, only enoyl-ACP reductase (Idpdb 1LXC) showed co-localization between the docked and ligand site predicted by I-TASSER (Fig. 1–2).
Thymidylate synthase ThyX is an enzyme implicated in prokaryotic cell DNA synthesis, with two principal sites: the FAD+ cofactor site (Asn16, Ser30, Thr55, His79, Glu86, and Arg165) and the dUMP substrate site (Arg78, Glu86, Ser88, Arg90, Arg147 and Arg174,) (34–36). The dock simulation revealed co-localization with Arg165, present in the FAD+ cofactor site. However, no residues were co-localized with the predicted site from the I-TASSER server (Table 4 and Fig. 2a – 2b). Despite this, this receptor was discarded as a potential molecular target for Oligoventin due to the positive ACE value, indicating that the interaction is thermodynamically unfavorable in vitro assays.
Pyridoxine 5-phosphate synthase is an enzyme associated with B6 vitamin synthesis, serving as an important cofactor in amino acid metabolism and glycogenolysis. This enzyme forms a complex with 1-deoxy-D-xylulose phosphate (dXP), involving residues such as Asp11, His12, Arg20, His52, Glu72, Thr103, Glu153, and His193 (37, 38). While the dock simulation did not reveal shared residues with the dXP site, the predicted model exhibited co-localization with Glu153, Glu72 and His193 (Table 4 and Fig. 1a).
Threonine dehydratase biosynthetic is an important enzyme in the biosynthesis of the amino acid threonine in E. coli. This structure contains a Pyridoxal 5-phosphate (PLP) binding site composed of Phe61, Lys62, Asn89, Gly241 and Ser315 (39, 40). Although the dock simulation did not reveal shared residues with PLP, all residues were shared with the predicted binding site (Table 4 and Fig. 1b).
Enoyl-ACP reductase is a key enzyme in the final step of type II fatty acid synthesis, specifically in the elongation phase. This molecule contains a cofactor binding site, with one binding site for NAD + comprising residues Ala16, Ala41, Leu45, Asp67, Val68, Ile95, and Ile121 and another for the nicotinamide ring comprising Thr147, Tyr148, Ala191, Gly192, and Ile194 (40–42). Both the dock simulation and predicted site revealed co-location with the residues Gly192 and Ile194, which are present in the nicotinamide ring binding site (Table 4 and Fig. 2c – 2d).
Fumarate reductase flavoprotein subunit is enzyme associated with bacteria respiration in oxygen absence, which are closely related to succinate dehydrogenase. This molecule has FAD+ cofactor site (Glu534) and subtracts (His504) (43, 44). Both residues not associated with Oligoventin in dock simulation results. In contrast, they are present in predicted binding site (Table 4 and Fig. 1c).
Cyclomaltodextrin glucanotransferase is enzyme associated to carbohydrates metabolism, important in cyclization of D-glucose. The substrate site is formed by Tyr100, Phe183, Tyr195, Asp229, Phe259 and Asp328 (45). Dock simulation not shows shared residues with substrate site, however Asp229 residues was shared with predicted bind site (Table 4 and Fig. 1d).
Therefore, molecular docking simulations suggest that Oligoventin interacts more strongly with Enoyl-ACP reductase (Idpdb 1LXC) and with less avidity with Thymidylate synthase ThyX (Idpdb 1O28), potentially disrupting the normal functions of these enzymes. This interaction could lead to a decrease in fatty acid and DNA biosynthesis, ultimately reducing microbial proliferation and impacting bacterial homeostasis.