Entropy-driven binding of octyl gallate in albumin: Failure in the application of temperature effect to distinguish dynamic and static fluorescence quenching

Author(s)

de Carvalho Bertozo, Luiza ^[1] ; Fernandes, Ana J. F. C. ^[1] ; Yoguim, Mauricio I. ^[1] ; Bolean, Mayte ^[2] ; Ciancaglini, Pietro ^[2] ; Ximenes, Valdecir F. ^[1]

Affiliation

^[1] UNESP Sao Paulo State Univ, Dept Chem, Fac Sci, Sao Paulo - Brazil

^[2] Univ Sao Paulo, Fac Philosophy Sci & Letters Ribeirao Preto, Dept Chem, Ribeirao Preto, SP - Brazil

• Document type: Journal article
• Source: JOURNAL OF MOLECULAR RECOGNITION; v. 33, n. 7 MAR 2020.
• Web of Science Citations: 0

Abstract

Fluorescence quenching is widely used to obtain association constants between proteins and ligands. This methodology is based on assumption that ground-state complex between protein and ligand is responsible for quenching. Here, we call the attention about the risk of using the temperature criterion for decision of applying or not fluorescence quenching data to measure association constants. We demonstrated that hydrophobic effect can be the major force involved in the interaction and, as such, superposes the well-established rationalization that host/guest complexation is weakened at higher temperatures due to loss of translational and rotational degrees of freedom. To do so, the complexation of bovine serum albumin with octyl gallate was studied by steady-state, time-resolved fluorescence spectroscopy and isothermal titration calorimetry. The results clearly demonstrated the complexation, even though the Stern-Volmer constant increased at higher temperatures (1.6 x 10(4) and 4.1 x 10(5) mol(-1) L at 20 degrees C and 40 degrees C), which could suggest a simple dynamic process and not complexation. The entropy-driven feature of the interaction was demonstrated by the unfavorable enthalpy ( increment H degrees = 104.4 kJmol(-1)) but favorable entropy ( increment S degrees = 447.5 Jmol(-1) K-1). The relevance of the ligand hydrophobicity was also evaluated by comparing ascorbic acid and its ester ascorbyl palmitate. Docking simulations showed a higher number of hydrophobic contacts and lower energy poses for the esters, confirming the experimental results. In conclusion, the well-established rationalization that host/guest complexation is weakened at higher temperatures is not straightforward for protein-ligand interactions. Hence, the temperature effect for a decision between static and dynamic quenching and its use to decide if a complexation at ground state is taking place between ligand and protein should not be used. (AU)

• FAPESP's process: 14/50926-0 - INCT 2014: biodiversity and natural products
• Grantee: Vanderlan da Silva Bolzani
• Support Opportunities: BIOTA-FAPESP Program - Thematic Grants
• FAPESP's process: 16/20549-5 - Development and application of fluorescent probes and probes based on circular dichroism for the interaction studies of ligands with protein, characterization of amyloid proteins and determination of enzymatic activity
• Grantee: Valdecir Farias Ximenes
• Support Opportunities: Regular Research Grants
• FAPESP's process: 16/22014-1 - Development of Fluorescent Probes for the Determination of Binding Sites on Albumin: Studies of the Relationship of the Molecular Structure, Association Constant and Specificity
• Grantee: Luiza de Carvalho Bertozo
• Support Opportunities: Scholarships in Brazil - Doctorate