Exploring interfacial water trapping in protein-ligand complexes with multithermal titration calorimetry

Publication date: Available online 4 January 2018 Source:Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics Author(s): Iris N. Serratos, Cesar Millán-Pacheco, Georgina Garza-Ramos, Gerardo Pérez-Hernández, Rafael A. Zubillaga In this work, we examine the hypothesis about how trapped water molecules at the interface between triosephosphate isomerase (TIM) and either of two phosphorylated inhibitors, 2-phosphoglycolate (2PG) or phosphoglycolohydroxamate (PGH), can explain the anomalous highly negative binding heat capacities (ΔC p,b ) of both complexes, TIM–2PG and TIM–PGH. We performed fluorimetric titrations of the enzyme with PGH inhibitor under osmotic stress conditions, using various concentrations of either osmolyte: sucrose, ethylene glycol or glycine betaine. We also analyze the binding processes under various stressor concentrations using a novel calorimetric methodology that allows ΔC p,b determinations in single experiments: Multithermal Titration Calorimetry. The binding constant of the TIM–PGH complex decreased gradually with the concentration of all osmolytes, but at diverse extents depending on the osmolyte nature. According to the osmotic stress theory, this decrease indicates that the number of water molecules associated with the enzyme increases with inhibitor binding, i.e. some solvent molecules became trapped. Additionally, the binding heat capacities became less negative at higher osmolyte concentrations, their final values depe...

Source: Biochimica et Biophysica Acta (BBA) Proteins and Proteomics - January 4, 2018 Category: Biochemistry Source Type: research