Mapping of TEMPO‑, PROXYL‑, and Phosphoryl-Functionalized Spin Probes into Biointerface Fatty Acid Recognition Sites...

A series of spin probes, bearing TEMPO, PROXYL or phosphorylated nitroxide paramagnetic groups attached to either terminal or internal position of an alkyl chain, are examined upon binding to bovine serum albumin, using an integrated spectroscopic, calorimetric, and computational approach. The structural diversity of spin probes allows a systematic investigation on how the type/position of paramagnetic moiety affect interaction. Electron paramagnetic resonance (EPR) and molecular docking reveal different dynamics of mid-chain and end-chain probes within distinct protein pockets. Mid-chain probes target deep hydrophobic sites, whereas end-chain probes reside near the protein-water interface. Phosphorylated nitroxides are strongly immobilized upon complexation, and lower the protein thermal stability. The highest enthalpy change of denaturation, linked to the lowest secondary structure perturbation, is determined by end-chain TEMPO. The collective results suggest that the nature and position of the paramagnetic moiety affect probe mobility and binding depth, while modulating the protein's conformational and thermal responses.