title: Environment sensitive fluorescent analogue of biologically active oxazoles differentially recognizes human serum albumin and bovine serum albumin: Photophysical and molecular modeling studies.
abstract: An environment sensitive fluorophore, 4-(5-(4-(dimethylamino)phenyl)oxazol-2-yl)benzoic acid (DMOBA), that closely mimics biologically active 2,5-disubstituited oxazoles has been designed to probe two homologous serum proteins, human serum albumin (HSA) and bovine serum albumin (BSA) by means of photophysical and molecular modeling studies. This fluorescent analogue exhibits solvent polarity sensitive fluorescence due to an intramolecular charge transfer in the excited state. In comparison to water, the steady state emission spectra of DMOBA in BSA is characterized by a greater blue shift (~10nm) and smaller Stokes' shift (~5980cm-1) in BSA than HSA (Stokes'shift~6600cm-1), indicating less polar and more hydrophobic environment of the dye in the former than the latter. The dye-protein binding interactions are remarkably stronger for BSA than HSA which is evident from higher value of the association constant for the DMOBA-BSA complex (Ka~5.2×106M-1) than the DMOBA-HSA complex (Ka~1.0×106M-1). Fӧrster resonance energy transfer studies revealed remarkably less efficient energy transfer (8%) between the donor tryptophans in BSA and the acceptor DMOBA dye than that (30%) between the single tryptophan moiety in HSA and the dye, which is consistent with a much larger distance between the donor (tryptophan)-acceptor (dye) pair in BSA (34.5Å) than HSA (25.4Å). Site specific competitive binding assays have confirmed on the location of the dye in Sudlow's site II of BSA and in Sudlow's site I of HSA, respectively. Molecular modeling studies have shown that the fluorescent analogue is tightly packed in the binding site of BSA due to strong steric complementarity, where, binding of DMOBA to BSA is primarily dictated by the van der Waals and hydrogen bonding interactions. In contrast, in HSA the steric complementarity is less significant and binding is primarily guided by polar interactions and van der Waals interactions appear to be less significant in the formation of the HSA-DMOBA complex. Electrostatic interactions contribute significantly in the binding of DMOBA to HSA (-2.09kcal/mol) compared to BSA (-0.47kcal/mol). Electrostatic surface potential calculation reveals that the DMOBA binding site within HSA is highly charged compared to BSA.
authors.affiliation: Department of Chemistry, West Bengal State University, Barasat, Kol-126, India.
authors.forename: Jyotirmay
authors.initials: J
authors.lastname: Maiti
authors.affiliation: Department of Chemistry, West Bengal State University, Barasat, Kol-126, India.
authors.forename: Suman
authors.initials: S
authors.lastname: Biswas
authors.affiliation: Department of Microbiology, West Bengal State University, Barasat, Kol-126, India.
authors.forename: Ankur
authors.initials: A
authors.lastname: Chaudhuri
authors.affiliation: Department of Microbiology, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India.
authors.forename: Sandipan
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Department of Microbiology, West Bengal State University, Barasat, Kol-126, India.
authors.forename: Sibani
authors.initials: S
authors.lastname: Chakraborty
authors.affiliation: Department of Chemistry, West Bengal State University, Barasat, Kol-126, India. Electronic address: ranjan.das68@gmail.com.
authors.forename: Ranjan
authors.initials: R
authors.lastname: Das
mesh_terms: D000818:Animals; D016880:Anisotropy; D001665:Binding Sites; D002417:Cattle; D004777:Environment; D031541:Fluorescence Resonance Energy Transfer; D005456:Fluorescent Dyes / Q000737:chemistry*; D006801:Humans; D007700:Kinetics; D008958:Models, Molecular; D062105:Molecular Docking Simulation; D010080:Oxazoles / Q000737:chemistry*; D012710:Serum Albumin, Bovine / Q000032:analysis* / Q000737:chemistry; D000075462:Serum Albumin, Human / Q000032:analysis* / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D055672:Static Electricity; D013816:Thermodynamics; D013997:Time Factors
chemical_list: D005456:Fluorescent Dyes; D010080:Oxazoles; D012710:Serum Albumin, Bovine; D000075462:Serum Albumin, Human
keywords: Association constant; Electrostatic interactions; Fluorophore; Steric complementarity; Van der Waals interactions