Understanding the binding and the reactivity of chromophoric guest within biological molecules is an important prerequisite for many biotechnological applications and for the control of the pharmacological activity/toxicity of drugs. In this frame knowledge of the structural features of the associated species is a key point. We recently reported a spectroscopic and computational method for the determination of the structure of drug-protein complexes in solution.1 This approach allowed us to rationalize the binding and the site-selective photoreactivity of an antibacterial quinolone, nalidixic acid, within human serum albumin (HSA). The drug-protein complexes were characterized as individual chemical species by global analysis of multiwavelength spectroscopic data using a numerical optimization procedure. Structural information was extracted from comparison of the experimental Induced Circular Dichroism (ICD) signals with the rotational strengths calculated by a quantum mechanical method combined with Molecular Mechanics (MM) and Molecular Dynamics (MD) modelling. In the present contribution we address the study of the interaction of a flavonoid derivative, Licochalcone-A (LA, see scheme), with HSA. Chalcone-like flavonoids are presently receiving attention in pharmacology for their anti-inflammatory, antibacterial, antifungal, antiviral, antitumor as well as antiparasitic activity.2 LA is a natural component extracted from Glycyrrhiza. We have elucidated LA binding to a natural carrier like HSA. The combined application of spectroscopic and computational methods of analysis has afforded a clear picture of the modes of association of the neutral LA molecule to HSA, evidencing interactions with specific protein aminoacids. The drug is primarily associated in Subdomain IIA where a strong interaction with Trp214 is established. At least two different positions of LA with respect to tryptophan are possible, one with ring B of the drug facing the aromatic ring of Trp214 and the other with ring A of LA in proximity of Trp214. In both cases LA is at ca. 4 Å from Trp214. This vicinity does not affect much the excited state deactivation paths of the bound drug that exhibits a slightly higher fluorescence quantum yield, but singlet and triplet lifetimes substantially similar to those of the free molecule. The secondary binding site is in subdomain IIIA. The carbonyl group of LA forms a strong H-bond with the OH substituent of Tyr411. This interaction reduces substantially the molecular degrees of freedom thereby accounting for the observed decrease of both radiative and nonradiative rate constants of the excited S1 singlet. The overall rigidity of the bound LA structure also causes a 6-fold lengthening of the triplet lifetime, possibly related to suppression of photoisomerization.
Licochalcone-A complexes with Human Serum Albumin: a spectroscopic and computational approach to the understanding of drug-protein interaction
I Manet;G Marconi;F Manoli;S Monti
2008
Abstract
Understanding the binding and the reactivity of chromophoric guest within biological molecules is an important prerequisite for many biotechnological applications and for the control of the pharmacological activity/toxicity of drugs. In this frame knowledge of the structural features of the associated species is a key point. We recently reported a spectroscopic and computational method for the determination of the structure of drug-protein complexes in solution.1 This approach allowed us to rationalize the binding and the site-selective photoreactivity of an antibacterial quinolone, nalidixic acid, within human serum albumin (HSA). The drug-protein complexes were characterized as individual chemical species by global analysis of multiwavelength spectroscopic data using a numerical optimization procedure. Structural information was extracted from comparison of the experimental Induced Circular Dichroism (ICD) signals with the rotational strengths calculated by a quantum mechanical method combined with Molecular Mechanics (MM) and Molecular Dynamics (MD) modelling. In the present contribution we address the study of the interaction of a flavonoid derivative, Licochalcone-A (LA, see scheme), with HSA. Chalcone-like flavonoids are presently receiving attention in pharmacology for their anti-inflammatory, antibacterial, antifungal, antiviral, antitumor as well as antiparasitic activity.2 LA is a natural component extracted from Glycyrrhiza. We have elucidated LA binding to a natural carrier like HSA. The combined application of spectroscopic and computational methods of analysis has afforded a clear picture of the modes of association of the neutral LA molecule to HSA, evidencing interactions with specific protein aminoacids. The drug is primarily associated in Subdomain IIA where a strong interaction with Trp214 is established. At least two different positions of LA with respect to tryptophan are possible, one with ring B of the drug facing the aromatic ring of Trp214 and the other with ring A of LA in proximity of Trp214. In both cases LA is at ca. 4 Å from Trp214. This vicinity does not affect much the excited state deactivation paths of the bound drug that exhibits a slightly higher fluorescence quantum yield, but singlet and triplet lifetimes substantially similar to those of the free molecule. The secondary binding site is in subdomain IIIA. The carbonyl group of LA forms a strong H-bond with the OH substituent of Tyr411. This interaction reduces substantially the molecular degrees of freedom thereby accounting for the observed decrease of both radiative and nonradiative rate constants of the excited S1 singlet. The overall rigidity of the bound LA structure also causes a 6-fold lengthening of the triplet lifetime, possibly related to suppression of photoisomerization.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
