COMPUTATIONAL ANALYSIS OF BIOACTIVE COMPOUNDS FROM CITRUS SINENSIS FRUIT PEELS TARGETING GYRASE B PROTEIN: PHYTOCHEMICAL PROFILING AND IN VITRO ANTIBACTERIAL ACTIVITY

Abstract

Citrus sinensis fruit peel, commonly regarded as agricultural waste, represents a rich source of bioactive phytochemicals with potential antibacterial applications. In this study, an integrated computational and experimental approach was employed to evaluate the antibacterial potential of C. sinensis peel extracts. Preliminary phytochemical screening revealed the presence of alkaloids, flavonoids, phytosteroids, terpenoids, quinones, and glycosides, while saponins were confined to methanolic and ethanolic extracts. Gas Chromatography-Mass Spectrometry (GC-MS) examination of the methanolic extract identified sixteen bioactive compounds. In silico ADME profiling showed that all compounds complied with Lipinski’s Rule of Five. Molecular docking against bacterial Gyrase B proteins (PDB IDs: 4URN and 1KZN) demonstrated strong binding energies, particularly for 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one against the Gram-positive (G^+ve) target (−5.5 kcal/mol) and (+)-limonene against the Gram-negative (G^-ve) target (−5.8 kcal/mol). The Methanol Extract of Citrus sinensis fruit peel (ME-CSFP) exhibited a concentration-dependent Antibacterial (AB) effect (30–100 µl). Greater inhibitory activity was observed against B. subtilis (6.0 ± 1.0 to 9.0 ± 1.2 mm) and S. aureus (5.0 ± 1.0 to 10.0 ± 1.0 mm), whereas comparatively lower susceptibility was noted in E. coli (4.33 ± 0.58 to 6.67 ± 2.52 mm) and K. pneumoniae (5.0 ± 1.0 to 6.67 ± 1.53 mm). The minimum inhibitory concentrations (MIC) of orange peel extract demonstrated stronger antibacterial activity against Gram-positive bacteria (Staphylococcus aureus 31.2 µg/ml; Bacillus subtilis 62.5  µg/ml) than against Gram-negative bacteria (Escherichia coli 250 µg/ml; Klebsiella pneumoniae 250 µg/ml). Overall, this study highlights the significant role of computational biology in prioritizing bioactive compounds and demonstrates that Citrus sinensis peel can serve as a promising, sustainable source and support its potential valorization in drug discovery.