title: Interaction of the anticancer plant alkaloid sanguinarine with bovine serum albumin.
abstract: BACKGROUND
  Interaction of the iminium and alkanolamine forms of sanguinarine with bovine serum albumin (BSA) was characterized by spectroscopic and calorimetric techniques.
  
  
  RESULTS
  Formation of strong complexes of BSA with both iminium and alkanolamine forms was revealed from fluorescence quenching of sanguinarine. Binding parameters calculated from Stern-Volmer quenching method revealed that the neutral alkanolamine had higher affinity to BSA compared to the charged iminium form. Specific binding distances of 3.37 and 2.38 nm between Trp 212 (donor) and iminium and alkanolamine forms (acceptor), respectively, were obtained from Forster resonance energy transfer studies. Competitive binding using the site markers warfarin and ibuprofen, having definite binding sites, demonstrated that both forms of sanguinarine bind to site I (subdomain IIA) on BSA. Sanguinarine binding alters protein conformation by reducing the α-helical organization and increasing the coiled structure, indicating a small but definitive partial unfolding of the protein. Thermodynamic parameters evaluated from isothermal titration calorimetry suggested that the binding was enthalpy driven for the iminium form but favoured by negative enthalpy and strong favourable entropy contributions for the alkanolamine form, revealing the involvement of different molecular forces in the complexation.
  
  
  CONCLUSIONS
  The results suggest that the neutral alkanolamine form binds to the protein more favourably compared to the charged iminium, in stark contrast to the reported DNA binding preference of sanguinarine.
authors.affiliation: Biophysical Chemistry Laboratory, Indian Institute of Chemical Biology, Council of Scientific and Industrial Research, Kolkata, West Bengal, India.
authors.forename: Maidul
authors.initials: M
authors.lastname: Hossain
authors.forename: Asma Yasmeen
authors.initials: AY
authors.lastname: Khan
authors.forename: Gopinatha
authors.initials: G
authors.lastname: Suresh Kumar
mesh_terms: D000042:Absorption; D000470:Alkaloids / Q000737:chemistry / Q000378:metabolism*; D000818:Animals; D000972:Antineoplastic Agents, Phytogenic / Q000737:chemistry / Q000378:metabolism*; D053119:Benzophenanthridines / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002151:Calorimetry; D002417:Cattle; D002942:Circular Dichroism; D004735:Energy Transfer; D007546:Isoquinolines / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D011485:Protein Binding; D017433:Protein Structure, Secondary; D012710:Serum Albumin, Bovine / Q000737:chemistry / Q000378:metabolism*; D013050:Spectrometry, Fluorescence; D013696:Temperature
chemical_list: D000470:Alkaloids; D000972:Antineoplastic Agents, Phytogenic; D053119:Benzophenanthridines; D007546:Isoquinolines; D012710:Serum Albumin, Bovine; C005705:sanguinarine