title: Binding of antioxidant flavone isovitexin to human serum albumin investigated by experimental and computational assays.
abstract: The flavonoids are a large class of polyphenolic compounds which occur naturally in plants where they are widely distributed. Isovitexin (ISO) is a glycosylated flavonoid that exhibits a potential antioxidant activity. Some recent studies have shown the pharmacokinetic activity of isovitexin in rat blood plasma, however, without detailing the molecular target that is linked and what physicochemical forces govern the interaction. In mammalians, the most abundant protein in blood plasma is the albumin and is not unlike with human, which human serum albumin (HSA) is the major extracellular protein and functions as a carrier of various drugs. The interaction between HSA and ISO was investigated using fluorescence, UV-vis absorbance, circular dichroism (CD), Fourier transform infrared spectroscopy (FT-IR) together with, computational methods like ab initio and molecular modeling calculation. Fluorescence quenching indicated that ISO location is within the hydrophobic pocket in subdomain IIA (site 1) of HSA, close to the Trp214 residue. The Stern-Volmer quenching constants determined at 288, 298 and 308K and its dependence on temperature indicated that the quenching mechanism was static. From the analysis of binding equilibrium were determined; the binding site number and binding constants, with the correspondent thermodynamic parameters, ΔH, ΔG and ΔS for HSA-ISO complex. Also, a second binding analysis, binding density function (BDF) method, which is independent of any binding model pre-established obtained similar results. The fluorescence resonance energy transfer estimated the distance between the donor (HSA-Trp214) and acceptor (ISO), while FT-IR and CD spectroscopy measured possible changes of secondary structure at the formation of the HSA-ISO complex. The optimized geometry of isovitexin calculation performed with its ground state by using DFT/B3LYP/6-311+G(d,p) method. The HSA-ISO complex interactions determined by molecular modeling tool corroborated with the thermodynamic analysis from the experimental data.
authors.affiliation: Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil; Centro Multiusuário de Inovação Biomolecular (CMIB), Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil. Electronic address: ykrocaruso@hotmail.com.
authors.forename: Ícaro Putinhon
authors.initials: ÍP
authors.lastname: Caruso
authors.affiliation: Instituto de Química (IQ), UNESP, Rua Prof. Francisco Degni 55, CEP 14800-900, Araraquara, SP, Brazil. Electronic address: vilegasw@gmail.com.
authors.forename: Wagner
authors.initials: W
authors.lastname: Vilegas
authors.affiliation: Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil; Centro Multiusuário de Inovação Biomolecular (CMIB), Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil. Electronic address: fatima@ibilce.unesp.br.
authors.forename: Fátima Perreira
authors.initials: FP
authors.lastname: de Souza
authors.affiliation: Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil; Centro Multiusuário de Inovação Biomolecular (CMIB), Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil. Electronic address: marcelo@ibilce.unesp.br.
authors.forename: Marcelo Andrés
authors.initials: MA
authors.lastname: Fossey
authors.affiliation: Departamento de Física, Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil; Centro Multiusuário de Inovação Biomolecular (CMIB), Instituto de Biociências, Letras e Ciências Exatas (IBILCE), UNESP, Rua Cristovão Colombo 2265, CEP 15054-000, São José do Rio Preto, SP, Brazil. Electronic address: mario@ibilce.unesp.br.
authors.forename: Marinônio Lopes
authors.initials: ML
authors.lastname: Cornélio
mesh_terms: D000975:Antioxidants / Q000737:chemistry*; D047310:Apigenin / Q000737:chemistry*; D001665:Binding Sites; D002942:Circular Dichroism / Q000379:methods; D005419:Flavonoids / Q000737:chemistry*; D005453:Fluorescence; D006801:Humans; D011485:Protein Binding; D012709:Serum Albumin / Q000737:chemistry*; D017550:Spectroscopy, Fourier Transform Infrared / Q000379:methods; D013816:Thermodynamics
chemical_list: D000975:Antioxidants; D005419:Flavonoids; D012709:Serum Albumin; D047310:Apigenin; C049772:isovitexin
keywords: Binding density function; Fluorescence spectroscopy; Human serum albumin; Isovitexin; Molecular modeling