Evidence of Self-Association and Conformational Change in Nisin Antimicrobial Polypeptide Solutions: A Combined Raman and Ultrasonic Relaxation Spectroscopic and Theoretical Study

Afrodite Tryfon; Panagiota Siafarika; Constantine Kouderis; Spyridon Kaziannis; Soghomon Boghosian; Angelos G Kalampounias

doi:10.3390/antibiotics12020221

Evidence of Self-Association and Conformational Change in Nisin Antimicrobial Polypeptide Solutions: A Combined Raman and Ultrasonic Relaxation Spectroscopic and Theoretical Study

Antibiotics (Basel). 2023 Jan 20;12(2):221. doi: 10.3390/antibiotics12020221.

Authors

Afrodite Tryfon¹, Panagiota Siafarika¹, Constantine Kouderis¹, Spyridon Kaziannis², Soghomon Boghosian³, Angelos G Kalampounias^{1

4}

Affiliations

¹ Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
² Department of Physics, University of Ioannina, GR-45110 Ioannina, Greece.
³ Department of Chemical Engineering, University of Patras, GR-26504 Patras, Greece.
⁴ University Research Center of Ioannina (URCI), Institute of Materials Science and Computing, GR-45110 Ioannina, Greece.

Abstract

The polypeptide Nisin is characterized by antibacterial properties, making it a compound with many applications, mainly in the food industry. As a result, a deeper understanding of its behaviour, especially after its dissolution in water, is of the utmost importance. This could be possible through the study of aqueous solutions of Nisin by combining vibrational and acoustic spectroscopic techniques. The velocity and attenuation of ultrasonic waves propagating in aqueous solutions of the polypeptide Nisin were measured as a function of concentration and temperature. The computational investigation of the molecular docking between Nisin monomeric units revealed the formation of dimeric units. The main chemical changes occurring in Nisin structure in the aqueous environment were tracked using Raman spectroscopy, and special spectral markers were used to establish the underlying structural mechanism. Spectral changes evidenced the presence of the dimerization reaction between Nisin monomeric species. The UV/Vis absorption spectra were dominated by the presence of π → π* transitions in the peptide bonds attributed to secondary structural elements such as α-helix, β-sheets and random coils. The analysis of the acoustic spectra revealed that the processes primarily responsible for the observed chemical relaxations are probably the conformational change between possible conformers of Nisin and its self-aggregation mechanism, namely, the dimerization reaction. The activation enthalpy and the enthalpy difference between the two isomeric forms were estimated to be equal to ΔH₁* = 0.354 ± 0.028 kcal/mol and ΔH₁⁰ = 3.008 ± 0.367 kcal/mol, respectively. The corresponding thermodynamic parameters of the self-aggregation mechanism were found to be ΔH₂* = 0.261 ± 0.004 kcal/mol and ΔH₂⁰ = 3.340 ± 0.364 kcal/mol. The effect of frequency on the excess sound absorption of Nisin solutions enabled us to estimate the rate constants of the self-aggregation mechanism and evaluate the isentropic and isothermal volume changes associated with the relaxation processes occurring in this system. The results are discussed in relation to theoretical and experimental findings.

Keywords: Nisin; Raman; polypeptides; self-association; ultrasonic relaxation spectroscopy.

Grants and funding

This research received no external funding.