Tryfon Afrodite, Siafarika Panagiota, Kouderis Constantine, Kaziannis Spyridon, Boghosian Soghomon, Kalampounias Angelos G
Department of Chemistry, University of Ioannina, GR-45110 Ioannina, Greece.
Department of Physics, University of Ioannina, GR-45110 Ioannina, Greece.
Antibiotics (Basel). 2023 Jan 20;12(2):221. doi: 10.3390/antibiotics12020221.
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 * = 0.354 ± 0.028 kcal/mol and = 3.008 ± 0.367 kcal/mol, respectively. The corresponding thermodynamic parameters of the self-aggregation mechanism were found to be * = 0.261 ± 0.004 kcal/mol and = 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.
多肽乳链菌肽具有抗菌特性，这使其成为一种有多种应用的化合物，主要应用于食品工业。因此，深入了解其行为，尤其是在其溶解于水之后的行为，至关重要。通过结合振动光谱和声学光谱技术研究乳链菌肽的水溶液，这一点才有可能实现。测量了在多肽乳链菌肽水溶液中传播的超声波的速度和衰减随浓度和温度的变化。对乳链菌肽单体单元之间分子对接的计算研究揭示了二聚体单元的形成。利用拉曼光谱追踪了在水环境中乳链菌肽结构发生的主要化学变化，并使用特殊的光谱标记来确定潜在的结构机制。光谱变化证明了乳链菌肽单体物种之间存在二聚化反应。紫外/可见吸收光谱主要由肽键中π→π跃迁决定，这些跃迁归因于二级结构元件，如α-螺旋、β-折叠和无规卷曲。声学光谱分析表明，导致观察到的化学弛豫的主要过程可能是乳链菌肽可能构象异构体之间的构象变化及其自聚集机制，即二聚化反应。活化焓和两种异构体形式之间的焓差估计分别等于 = 0.354±0.028千卡/摩尔和 = 3.008±0.367千卡/摩尔。发现自聚集机制的相应热力学参数为* = 0.261±0.004千卡/摩尔和 = 3.340±0.364千卡/摩尔。频率对乳链菌肽溶液过量吸声的影响使我们能够估计自聚集机制的速率常数，并评估与该系统中发生的弛豫过程相关的等熵和等温体积变化。结合理论和实验结果对这些结果进行了讨论。
