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.Communicated by Ramaswamy H. Sarma.

Spectroscopic aspects on the interaction of nisin with serum albumin: thermodynamic and kinetic studies.

Introduction: Nisin is a bacteriocin produced by Streptococcus and Lactococcus species and has antimicrobial activity against other bacteria. Nisin omits the need to use chemical preservatives in food due to its biological preserving properties. Methods: In the present in vitro study, we investigated nisin interaction with bovine serum albumin (BSA) using fluorescence spectroscopy and surface plasmon resonance (SPR) analysis to obtain information about the mechanisms of BSA complex formation with nisin. Results: The BSA fluorescence intensity values gradually diminished with rising nisin concentration. The BSA fluorescence quenching analysis indicated that a combined quenching mechanism plays the main role. Finally, the Kb values were reduced with increasing temperature, which is demonstrative of nisin-BSA complex stability decrease at high temperatures. The negative values of ΔH° and ΔS° showed that hydrogen bonds and van der Waals forces are the foremost binding force between BSA and nisin. Meanwhile, the negative values of ΔG° demonstrated the exothermic and random nature of the reaction process. The results of the SPR verified the gained results through the fluorescence spectroscopy investigation, which denoted that the BSA affinity to nisin diminished upon increasing temperature. Conclusion: Overall, fluorescence spectroscopy and SPR results showed that the BSA interaction with nisin decreased with rising temperatures.