EVALUATION OF INTERACTIONS BETWEEN NATURAL COMPOUNDS AND THE HUMAN RESPIRATORY SYNCYTIAL VIRUS M PROTEIN

Human respiratory syncytial virus (RSV) is a leading cause of hospitalization due to respiratory diseases in children under 5 years, primarily during the first infection, and causes pneumonia or bronchiolitis. Effective treatments are currently unavailable. The Matrix (M) protein, a vital component of the virion, consists of 256 amino acid residues, is phosphorylated and non-glycosylated, and surrounds the ribonucleoprotein complex (RNP) located between this complex and the viral lipid bilayer, playing a key role in viral budding and dissemination. Our group focuses on natural compounds interacting with RSV proteins, with promising in vitro cell culture results. Given the importance of the M protein in viral budding, this study aimed to map natural compounds' interactions with the M protein. The protein was recombinantly expressed from E.coli RIL DE3 and purified via affinity chromatography and molecular exclusion. STD-NMR, Circular Dichroism, and Fluorescence Spectroscopy were used for experimental tests with natural compounds, while Molecular Docking and Molecular Dynamics were performed to characterize the interaction between the M protein and ligands. Results indicate that the hydrophobic effect primarily drives the interaction between compounds and the M protein, enhancing entropy and enthalpy but not inactivating the M protein, as shown by Circular Dichroism. The highest dissociation constants were observed for Chalcone and Coumarin, followed by Kaempferol (5.7x10⁴; 5.7x10⁴; and 3.4x10⁴ M^-1, respectively). These molecules maintain the protein's secondary and tertiary structures, slightly altering local residue flexibility. Additionally, the number of contacts and hydrogen bonds between each ligand's atoms and the M protein ranged from 600 to 900, indicating that the interaction site remains conformationally stable. These interactions occur at the dimeric interface of the protein, and although they do not cause monomer dissociation, they could potentially hinder the M protein's binding with other viral and cellular proteins during infection.