Spectroscopic investigation of conformational changes in urease caused by interaction with humic acid

文献类型： 外文期刊

第一作者： Li, Yan

作者： Li, Yan;Li, Yan;Wu, Chunyan;Tang, Xu;Chen, Yi;Koopal, Luuk K.;Chai, Yanjun;Tan, Wenfeng;Tan, Wenfeng;Chen, Yi

作者机构：

关键词： Humic acid; Urease conformation; pH; Ionic strength; Spectroscopic techniques

期刊名称：COLLOIDS AND SURFACES B-BIOINTERFACES （ 影响因子：5.999； 五年影响因子：5.596 ）

ISSN： 0927-7765

年卷期： 2022 年 215 卷

页码：

收录情况： SCI

摘要： Urease in soil interacts with humic acid (HA), which results in a change of the enzymatic activity and stability. However, knowledge on the conformational change of urease in the presence of HA is still lacking. Therefore, the structure of urease (net zero charge at pH 5.2) interacting with HA and the microenvironments of the tyrosine (Tyr) and tryptophane (Trp) residues were investigated at pH 6.7 and 8.0 and 0.5 and 50 mmol L-1 KCl using spectroscopic techniques. Fluorescence intensity of urease was progressively inhibited by HA with increasing mass ratio f of HA/urease. Moreover, quenching of urease fluorescence by HA was strongest at pH 6.7 (and 50 mmol L-1 KCl) where the hydrophobic attraction was counteracted by only a weak electrostatic repulsion. HA exerted only a minor effect on the positions of the maximum excitation bands for Tyr and Trp residues, indicating insignificant changes in the microenvironment of these residues in the presence of HA. At pH 6.7, the amide I and amide II bands were inhibited by HA. Curve-fitting of the amide I band of urease in complexes indicated that the percentages of alpha-helix, beta-sheet and beta-turn were changed. At pH 8 HA had little effect on the circular dichroism and attenuated total reflectance Fourier transform infrared spectra of urease. At this pH the interaction between urease and HA was weak due to the relatively strong electrostatic repulsion and the conformational change was insignificant. The present results increase our understanding of negatively charged protein behavior in natural environments dominated by humic substances.

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