Thermodynamics, structure, and antibacterial activity of the decavanadate-lysozyme complex

This study investigated the influence of highly charged polyanions on protein structure and function using the lysozyme-decavanadate ([V₁₀O₂₈]^6-) system as a model. To elucidate the thermodynamic, structural, and functional consequences of these interactions, the binding was comprehensively characterized using an integrated experimental and computational approach, including isothermal titration calorimetry (ITC), steady-state fluorescence spectroscopy (SF), electrospray ionization mass spectrometry (ESI-MS), circular dichroism spectroscopy (CD), and molecular dynamics (MD) simulations. The formation of a 2:1 ([V₁₀O₂₈]^6-:lysozyme) complex at pH 5.0 was established using ITC and SF data, with MD simulations localizing the primary binding site to the positively charged C-terminal region of the protein. The complex is predominantly stabilized by electrostatic interactions, consistent with the observed enthalpy-driven binding thermodynamics. Analysis of the CD spectra indicated that the binding event triggered substantial conformational changes in lysozyme, characterized primarily by a decrease in the α-helical structure. Despite this structural rearrangement, the catalytic activity of lysozyme remained largely unaffected. Finally, biological tests revealed that the mixture of [V₁₀O₂₈]^6- and lysozyme displays enhanced antibacterial activity relative to the individual components, with a greater enhancement of lytic action observed against Gram-positive bacteria (B. subtilis, S. aureus) than against Gram-negative strains (E. coli, P. aeruginosa).