Probing binding mode between sodium acid pyrophosphate and albumin: multi-spectroscopic and molecular docking analysis

Sodium acid pyrophosphate (SAPP) food additive is widely used as a preservative, bulking agent, chelating agent, emulsifier and pH regulator. It is also used as an improver of color and water retention capacity in the processing of various types of seafood, canned food, cooked meat and flour products. For the first time, we evaluated the SAPP interaction with bovine serum albumin (BSA) using spectroscopic methods including UV-Vis absorption, fluorescence spectroscopy, and surface plasmon resonance, and docking analysis to understand the mechanisms of complex formation and binding. The fluorescence intensity of BSA reduces when titrated with various concentrations of SAPP by forming a complex with BSA via a static quenching mechanism. The binding constant between BSA and SAPP decreased from 123,300 to 15,800 (M−1) with rising temperature, which indicates a decrement in complex formation owing to the interaction of SAPP with BSA. A negative ΔG° value means that SAPP binds spontaneously to BSA at all temperatures, and both ΔH° and ΔS° negative values indicate that hydrogen bonds (H-bonding) and van der Waals forces are the primary forces involved in the binding processes. The UV-Vis spectrum of BSA reduced upon increasing SAPP concentrations due to forming a new ground state complex between SAPP and BSA. Molecular docking study shows that residues Arg256, Ser259, Ser286, Ile 289 and Ala 290 play an important role in SAPP binding process to site I (subdomain IIA) of BSA through H-bonding and van der Waals forces, which is supported by the thermodynamic study.