Cyclo(L-Ala-L-Gly)

Cyclo(l-Ala-l-Pro) inhibits aflatoxin production in aflatoxigenic fungi without affecting fungal growth. The mode of action of cyclo(l-Ala-l-Pro) in inhibiting aflatoxin production of Aspergillus flavus was investigated. A glutathione S-transferase (GST) of the fungus, designated AfGST, was identified as a binding protein of cyclo(l-Ala-l-Pro) in an experiment performed using cyclo(l-Ala-l-Pro)-immobilized Sepharose beads. Cyclo(l-Ala-l-Pro) specifically bound to recombinant AfGST and inhibited its GST activity. Ethacrynic acid, a known GST inhibitor, inhibited the GST activity of recombinant AfGST and aflatoxin production of the fungus. Ethacrynic acid reduced the expression level of AflR, a key regulatory protein for aflatoxin production, similar to cyclo(l-Ala-l-Pro). These results suggest that cyclo(l-Ala-l-Pro) inhibits aflatoxin production by affecting GST function in A. flavus, and that AfGST inhibitors are possible candidates as selective aflatoxin production inhibitors.

Peroxisome proliferator-activated receptor (PPAR) expression has been implicated in pathological states such as cancer, inflammation, diabetes, and neurodegeneration. We isolated natural PPAR agonists-eight 2,5-diketopiperazines-from the jellyfish-derived fungus Aspergillus flavus. Cyclo-(L-Pro-L-Phe) was the most potent PPAR-γ activator among the eight 2,5-DKPs identified. Cyclo-(L-Pro-L-Phe) activated PPAR-γ in Ac2F rat liver cells and SH-SY5Y human neuroblastoma cells. The neuroprotective effect of this partial PPAR-γ agonist was examined using the 3-(4, 5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, lactate dehydrogenase release, and the Hoechst 33342 staining assay in SH-SY5Y cells. Our findings revealed that cyclo-(L-Pro-L-Phe) reduced hydrogen peroxide-induced apoptosis as well as the generation of reactive oxygen species. Rhodamine 123 staining and western blotting revealed that cyclo-(L-Pro-L-Phe) prevented the loss of mitochondrial membrane potential and inhibited the activation of mitochondria-related apoptotic proteins, such as caspase 3 and poly (ADP-ribose) polymerase. Moreover, cyclo-(L-Pro-L-Phe) inhibited the activation and translocation of nuclear factor-kappa B. Thus, the partial PPAR-γ agonist cyclo-(L-Pro-L-Phe) demonstrated potential neuroprotective activity against oxidative stress-induced neurodegeneration in SH-SY5Y cells.

Fungal spoilage led to a considerable economic loss of foodstuff which ultimately affects public health due to mycotoxins production. Moreover, the consumption of commercial antifungal drugs creates side effects and develops antifungal resistance. To overcome these challenges, the current work was aimed to investigate novel antifungal cyclic dipeptide (CDP) from Lactobacillus coryniformis (Loigolactobacillus coryniformis) BCH-4. CDPs have flexible, cyclic, and stable conformation. The proline-based CDPs provide additional structural compatibility and bio-functional values. Keeping in view, high-performance liquid chromatography (HPLC) was performed to explore cyclo(L-Leu-L-Pro) from L. coryniformis BCH-4. The HPLC detected concentration (135 ± 7.07 mg/mL) exhibited in vitro antifungal activity of 5.66 ± 0.57 mm (inhibitory zone) against Aspergillus flavus. Based on these results, cyclo(L-Leu-L-Pro) was used as a bioprotectant for selected food samples (grapes, lemon, cashew nuts, and almonds). A significant impact of cyclo(L-Leu-L-Pro) was observed in contrast with MRS broth (control) and cell-free supernatant. In silico molecular docking analysis of this CDP was carried out against FAD glucose dehydrogenase, dihydrofolate reductase, and urate oxidase of A. flavus as target proteins. Among these proteins, FAD glucose dehydrogenase exerted strong interactions with cyclo(L-Leu-L-Pro) having S-score of - 8.21. The results evaluated that the detected CDP has strong interactions with selected proteins, causing excellent growth inhibition of A. flavus. Therefore, cyclo(L-Leu-L-Pro) could be used as a potent bioprotectant against food-borne pathogenic fungi.