Antioxidant and antidiabetic activities of proteins from Moringa oleifera

Abstract

Moringa oleifera is among the highly reported medicinal plant with abundant health benefits mostly shown by its leaf and seed. Currently, research on antioxidant and antidiabetic activities of the plant have been focused on its aqueous and solvent extracts. In fact, study on proteins from this plant is still limited. Furthermore, the discovery of Moringa protein’s antioxidant and antidiabetic activity supports its potential application in the medical sector. Hence, protein from Moringa’s leaf, seed and petiole were extracted before their antioxidant and antidiabetic activity were established. Determination of the best protein extraction method for different parts of Moringa revealed that all three parts were best extracted using Tris buffer with incorporation of dithiothreitol (DTT) and phenylmethylsulfonyl fluoride (PMSF). Next, 1D proteomics using Sodium Dodecyl Sulfate Polyacrylamide Gel Electrophoresis (SDS-PAGE) and in-solution digestion prior to Liquid Chromatography–Mass Spectrometry (LC-MS/MS) analysis were subsequently done to establish the protein profiling of different plant parts. There were 144, 125, and 122 proteins identified from the leaf, seed and petiole, respectively. Interestingly, few peptides responsible for antioxidant and anticancer activity were identified. These proteins include maternally expressed gene 5, glutathione biosynthesis and catalase from the leaf, myrosinase, thioglucoside glucosidase and peroxidase in the seed while catalase, peroxidase, and glutathione transferase from the petiole. Furthermore, the antioxidant ability of both protein and crude extracts from Moringa’s leaf, seed and petiole was determined via Ferric Reducing Antioxidant Power (FRAP) and 2, 2-diphenyl-1-picryl-hydrazyl-hydrate (DPPH) free radical assay. Since the protein extract of leaf and petiole exhibited higher reducing activity compared to the crude extract, potential pharmacological activity of the protein extract was anticipated. Thus, the antidiabetic activity of the protein extracted from leaf, petiole, and seed were further studied using a-amylase and a-glucosidase inhibition assays. The highest a-amylase inhibition activity of 96% was conferred by the seed while highest a-glucosidase inhibition activity of 92% was conferred by the leaf. Moreover, a high potential antidiabetic agent namely Transketolase (TKT) enzyme was identified in the petiole. In silico analysis of TKT indicated it to be a thermostable protein upon molecular dynamics (MD) simulation at 310 K, 373 K, 423 K, 453 K, and 473 K. The findings of this study provide proteomic analysis of M. oleifera’s leaf, seed and petiole. These protein extracts were proven to possess both antioxidant and antidiabetic activity and further supported by the protein profiling results. In fact, bioinformatics findings on TKT provide meaningful insight towards potential drug development as it pose potential roles in combating diabetes.