Antimicrobial RNases are small cationic proteins belonging to the vertebrate RNase A superfamily and endowed with a wide range of antipathogen activities. Vertebrate RNases, while sharing the active site architecture, are found to display a variety of noncatalytical biological properties, providing an excellent example of multitask proteins. The antibacterial activity of distant related RNases suggested that the family evolved from an ancestral host-defence function. The review provides a structural insight into antimicrobial RNases, taking as a reference the human RNase 3, also named eosinophil cationic protein (ECP). A particular high binding affinity against bacterial wall structures mediates the protein action. In particular, the interaction with the lipopolysaccharides at the Gram-negative outer membrane correlates with the protein antimicrobial and specific cell agglutinating activity. Although a direct mechanical action at the bacteria wall seems to be sufficient to trigger bacterial death, a potential intracellular target cannot be discarded. Indeed, the cationic clusters at the protein surface may serve both to interact with nucleic acids and cell surface heterosaccharides. Sequence determinants for ECP activity were screened by prediction tools, proteolysis and peptide synthesis. Docking results are complementing the structural analysis to delineate the protein anchoring sites for anionic targets of biological significance.

Human antimicrobial RNases, which belong to the vertebrate RNase A superfamily and are secreted upon infection, display a wide spectrum of antipathogen activities. In this work, we examined the antifungal activity of the eosinophil RNase 3 and the skin‐derived RNase 7, two proteins expressed by innate cell types that are directly involved in the host defense against fungal infection. Candida albicans has been selected as a suitable working model for testing RNase activities toward a eukaryotic pathogen. We explored the distinct levels of action of both RNases on yeast by combining cell viability and membrane model assays together with protein labeling and confocal microscopy. Site‐directed mutagenesis was applied to ablate either the protein active site or the key anchoring region for cell binding. This is the first integrated study that highlights the RNases’ dual mechanism of action. Along with an overall membrane‐destabilization process, the RNases could internalize and target cellular RNA. The data support the contribution of the enzymatic activity for the antipathogen action of both antimicrobial proteins, which can be envisaged as suitable templates for the development of novel antifungal drugs. We suggest that both human RNases work as multitasking antimicrobial proteins that provide a first line immune barrier.

Amphibian skin is a rich source of natural compounds with diverse antimicrobial and immune defense properties. Our previous studies showed that the frog skin secretions obtained by skin micro-organs from various species of Colombian anurans have antimicrobial activities against bacteria and viruses. We purified for the first time two antimicrobial peptides from the skin micro-organs of the Orinoco lime treefrog (Sphaenorhynchus lacteus) that correspond to Buforin II (BF2) and Frenatin 2.3S (F2.3S). Here, we have synthesized the two peptides and tested them against Gram-negative and Gram-positive bacteria, observing an effective bactericidal activity at micromolar concentrations. Evaluation of BF2 and F2.3S membrane destabilization activity on bacterial cell cultures and synthetic lipid bilayers reveals a distinct membrane interaction mechanism. BF2 agglutinates E. coli cells and synthetic vesicles, whereas F2.3S shows a high depolarization and membrane destabilization activities. Interestingly, we found that F2.3S is able to internalize within bacterial cells and can bind nucleic acids, as previously reported for BF2. Moreover, bacterial exposure to both peptides alters the expression profile of genes related to stress and resistance response. Overall, these results show the multifaceted mechanism of action of both antimicrobial peptides that can provide alternative tools in the fight against bacterial resistance.

Non-centrifugal cane sugar (NCS) is a traditional sweetener in most sugarcane regions of the world. In Colombia, this product has a socio-economic importance due to the extensive cultivation area and the high consumption rate per capita. NCS traditional processing involves consecutive stages of thermal processing that begin with juice extraction, clarification, evaporation, and finish with syrup crystallization into a solid commercial product, identified as NCS. Sugarcane is known to have a natural content of polyphenols, amino acids, vitamins, minerals, and complex sugars, some of which are reported as antioxidant and antiproliferative agents thought to be responsible for the product’s bioactive profile. There is evidence to suggest that traditional thermal processing to obtain NCS leads to a considerable decrease in the contents of these bioactive compounds, mainly due to uncontrolled process variables such as temperature. Accordingly, the aim of this study was to assess and compare the bioactivity of sugarcane (SC) derivatives produced under controlled thermal conditions versus the traditional method. To achieve this goal, we evaluated the cytotoxic, antioxidant, and neuroprotective effects of varying concentrations of SC derivatives in an in vitro induced Parkinson’s model. Results demonstrate non-cytotoxic activity on the cellular model by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and LDH assays, even at the highest tested concentration of 8 mg/mL, for all SC derivatives. The effect of SC derivatives on the induced oxidative stress model showed a biological reversion and recovering effect of the mitochondrial membrane potential and a halting of the progress into the early apoptosis phase. In conclusion, we demonstrated that the bioactive compounds present in SC derivatives obtained by a process under controlled temperature conditions are largely preserved, and even their biological activities are enhanced compared with SC derivatives obtained by the traditional thermal evaporation of SC-juice.