Spectroscopic and Molecular Modeling Studies on the Binding of the Flavonoid Luteolin and Human Serum Albumin Zuzana Jurasekova, 1 Giancarlo Marconi, 2 Santiago Sanchez-Cortes, 1 Armida Torreggiani 2 1 Instituto de Estructura de la Materia, CSIC, Serrano 121, Madrid 280 06, Spain 2 Istituto I.S.O.F. (C.N.R.), via P. Gobetti 101, Bologna 401 29, Italy Received 21 May 2009; revised 18 June 2009; accepted 21 June 2009 Published online 14 July 2009 in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/bip.21278 This article was originally published online as an accepted preprint. The ‘‘Published Online’’ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley. com INTRODUCTION F lavonoids, also referred as vitamin P, represent a large and differentiated group of phenolic compounds ubiquitous in plants and therefore common in a great variety of fruits, vegetables, and beverages. 1 Beneficial effects of flavonoids on human health have gained increasing interest in the last years. 2 Most of the benefits have been associated to the antioxidant action of these polyphe- nols. 3–6 Owing to their phenolic nature, flavonoids are quite polar but poorly water soluble and their absorption could be scarce. This aspect has limited their use in the pharmaceuti- cal field. Among the various classes of flavonoids, flavones, widely present in herbaceous plants are characterized by a 2- phenyl-1,4-benzopyrone skeleton and are usually classified by the number and position of its hydroxyl substituents. Lu- teolin (LUT), i.e. 5,7,3 0 ,4 0 -tetrahydroxyflavone (Figure 1), is one of the more common flavones and has been investigated for its numerous pharmaceutical properties. 7–9 In fact, it has been shown to possess antioxidant, anti-inflammatory, and antitumorigenic properties; it is a potent hypoglycemic agent, improves insulin sensitivity and may help to promote healthy blood glucose levels. 10,11 LUT is also the main component and responsible for the characteristic yellow color of weld, a pigment derived by the leaves and stem of Reseda luteola L, that was treated with mordant solutions, has been used from the beginning of the Spectroscopic and Molecular Modeling Studies on the Binding of the Flavonoid Luteolin and Human Serum Albumin Additional Supporting Information may be found in the online version of this article. Correspondence to: Armida Torreggiani; e-mail: torreggiani@isof.cnr.it ABSTRACT: Luteolin (LUT) is a polyphenolic compound, found in a variety of fruits, vegetables, and seeds, which has a variety of pharmacological properties. In the present contribution, binding of LUT to human serum albumin (HSA), the most abundant carrier protein in the blood, was investigated with the aim of describing the binding mode and parameters of the interaction. The application of circular dichroism, UV-Vis absorption, fluorescence, Raman and surface-enhanced Raman scattering spectroscopy combined with molecular modeling afforded a clear picture of the association mode of LUT to HSA.Specific interactions with protein amino acids were evidenced. LUT was found to be associated in subdomain IIA where an interaction with Trp-214 is established. Hydrophobic and electrostatic interactions are the major acting forces in the binding of LUT to HSA. The HSA conformations were slightly altered by the drug complexation with reduction of a-helix and increase of b-turns structures, suggesting a partial protein unfolding. Also the configuration of at least two disulfide bridges were altered. Furthermore, the study of molecular modeling afforded the binding geometry. # 2009 Wiley Periodicals, Inc. Biopolymers 91: 917–927, 2009. Keywords: human serum albumin; binding site; luteolin; raman spectroscopy; molecular modeling Contract grant sponsor: European Community (Sixth Framework Programme for Marie Curie Early Stage Research Training Fellowship) Contract grant number: MEST-CT-2004-513915 V V C 2009 Wiley Periodicals, Inc. Biopolymers Volume 91 / Number 11 917