Biomolecular strategy for designing antibiotic–silver nanoparticles conjugate via nitrate reductase mediated β-lactamase inhibition with molecular docking insights

In this study, mechanistic analysis using SDS-PAGE identified a 58 kDa protein as the biomolecule responsible for AgNPs biosynthesis and capping. Colorimetric microplate-based assay confirmed the protein as nitrate reductase, with structural preservation evidenced by a 29.68% activity increase (1.856 to 2.407 U/g) following AgNPs synthesis. Functionalization of AgNPs with ampicillin was indicated by SPR shift from 422.5 to 340.5 nm and disappearance of the FTIR band at 1736 cm⁻¹. Amp-AgNPs conjugate was stable (3 months), semi-spherical crystalline, polydisperse (PDI: 0.192), average diameter of 27.26 nm, zeta potential of - 24.9 mV, and showed broad pH (1-9) and thermal (5-55 °C) stability. Docking analysis revealed strong binding of ampicillin within the nitrate reductase catalytic pocket through hydrogen bonding, hydrophobic, and electrostatic interactions, confirming the conjugate stability. Amp-AgNPs (50 µg/mL) exhibited potent antibacterial activity against β-lactamase-producing bacteria with inhibition zones of 27.3 mm (Escherichia coli), 25.0 mm (Enterococcus faecalis), and 26.3 mm (Staphylococcus aureus), and MICs of 3.3, 4.7, and 4.3 µg/mL, respectively. SEM analysis revealed severe structural changes, indicating synergistic membrane disruption and antibiotic delivery. Amp-AgNPs potently inhibited β-lactamase in the iodometric assay, supporting their potential as alternative therapeutic agents. Future studies should focus on in vivo efficacy and expand this strategy to additional drug delivery applications.