title: Exploring the interaction of the photodynamic therapeutic agent thionine with bovine serum albumin: multispectroscopic and molecular docking studies.
abstract: This study explores the binding interaction of thionine (TH) with bovine serum albumin (BSA) under physiological conditions (pH 7.40) using absorption, emission, synchronous emission, circular dichroism (CD) and three-dimensional (3D) emission spectral studies. The results of emission titration experiments revealed that TH strongly quenches the intrinsic emission of BSA via a static quenching mechanism. The apparent binding constant (K) and number of binding sites (n) were calculated as 2.09 × 10(5) dm(3) /mol and n ~1, respectively. The negative free energy change value for the BSA-TH system suggested that the binding interaction was spontaneous and energetically favourable. The results from absorption, synchronous emission, CD and 3D emission spectral studies demonstrated that TH induces changes in the microenvironment and secondary structure in BSA. Site marker competitive binding experiments revealed that the binding site of TH was located in subdomain IIA (Sudlow site I) of BSA. The molecular docking study further substantiates Sudlow site I as the preferable binding site of TH in BSA.
authors.affiliation: Department of Chemistry, Bharathiar University, Coimbatore, India.
authors.forename: Perumal
authors.initials: P
authors.lastname: Manivel
authors.affiliation: Department of Bioinformatics, Bharathiar University, Coimbatore, India.
authors.forename: Shanmugam
authors.initials: S
authors.lastname: Anandakumar
authors.affiliation: Department of Chemistry, Bharathiar University, Coimbatore, India.
authors.forename: Malaichamy
authors.initials: M
authors.lastname: Ilanchelian
mesh_terms: D001665:Binding Sites; D001667:Binding, Competitive; D002942:Circular Dichroism; D062105:Molecular Docking Simulation; D010640:Phenothiazines / Q000737:chemistry* / Q000378:metabolism; D010778:Photochemotherapy / Q000379:methods; D017319:Photosensitizing Agents / Q000737:chemistry / Q000378:metabolism; D017433:Protein Structure, Secondary; D012710:Serum Albumin, Bovine / Q000737:chemistry* / Q000378:metabolism; D013056:Spectrophotometry, Ultraviolet
chemical_list: D010640:Phenothiazines; D017319:Photosensitizing Agents; D012710:Serum Albumin, Bovine; C009469:thionine
keywords: bovine serum albumin; circular dichroism; emission spectroscopy; molecular docking; thionine