title: Fluorescence and Docking Studies of the Interaction between Human Serum Albumin and Pheophytin.
abstract: In the North of Brazil (Pará and Amazonas states) the leaves of the plant Talinum triangulare (popular: cariru) replace spinach as food. From a phytochemical point of view, they are rich in compounds of the group of pheophytins. These substances, related to chlorophyll, have photophysical properties that give them potential application in photodynamic therapy. Human serum albumin (HSA) is one of the main endogenous vehicles for biodistribution of molecules by blood plasma. Association constants and thermodynamic parameters for the interaction of HSA with pheophytin from Talinum triangulare were studied by UV-Vis absorption, fluorescence techniques, and molecular modeling (docking). Fluorescence quenching of the HSA's internal fluorophore (tryptophan) at temperatures 296 K, 303 K, and 310 K, resulted in values for the association constants of the order of 10⁴ L∙mol(-1), indicating a moderate interaction between the compound and the albumin. The negative values of ΔG° indicate a spontaneous process; ΔH° = 15.5 kJ∙mol(-1) indicates an endothermic process of association and ΔS° = 0.145 kJ∙mol(-1)∙K(-1) shows that the interaction between HSA and pheophytin occurs mainly by hydrophobic factors. The observed Trp fluorescence quenching is static: there is initial non-fluorescent association, in the ground state, HSA:Pheophytin. Possible solution obtained by a molecular docking study suggests that pheophytin is able to interact with HSA by means of hydrogen bonds with three lysine and one arginine residues, whereas the phytyl group is inserted in a hydrophobic pocket, close to Trp-214.
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. otavio_ufrrj@hotmail.com.
authors.forename: Otávio Augusto
authors.initials: OA
authors.lastname: Chaves
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. anamorim16@gmail.com.
authors.forename: Ana Paula de O
authors.initials: AP
authors.lastname: Amorim
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. larissa_hec@hotmail.com.
authors.forename: Larissa H E
authors.initials: LH
authors.lastname: Castro
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. santanna@ufrrj.br.
authors.forename: Carlos Mauricio R
authors.initials: CM
authors.lastname: Sant'Anna
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. mccdeo@gmail.com.
authors.forename: Márcia C C
authors.initials: MC
authors.lastname: de Oliveira
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. dari@ufrrj.br.
authors.forename: Dari
authors.initials: D
authors.lastname: Cesarin-Sobrinho
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. jcnetto.ufrrj@gmail.com.|Instituto Nacional de Metrologia, Qualidade e Tecnologia-INMETRO, Divisão de Metrologia Química, 25250-020 Duque de Caxias-RJ, Brazil. jcnetto.ufrrj@gmail.com.
authors.forename: José Carlos
authors.initials: JC
authors.lastname: Netto-Ferreira
authors.affiliation: Departamento de Química, Universidade Federal Rural do Rio de Janeiro, BR 465, km 47, 23890-000 Seropédica-RJ, Brazil. aureliobf@uol.com.br.
authors.forename: Aurélio B B
authors.initials: AB
authors.lastname: Ferreira
mesh_terms: D001665:Binding Sites; D029421:Cactaceae / Q000737:chemistry*; D006801:Humans; D006860:Hydrogen Bonding; D008958:Models, Molecular; D062105:Molecular Docking Simulation / Q000379:methods*; D015394:Molecular Structure; D010674:Pheophytins / Q000737:chemistry*; D010778:Photochemotherapy; D018515:Plant Leaves / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry*; D013050:Spectrometry, Fluorescence / Q000379:methods
chemical_list: D010674:Pheophytins; D012709:Serum Albumin
keywords: Talinum triangulare; docking; fluorescence spectroscopy; human serum albumin; pheophytin