The molecular insights into protein adsorption on hematite surface disclosed by in-situ ATR-FTIR/2D-COS study.

Matheus Sampaio C Barreto,Evert J Elzinga,Luís Reynaldo F Alleoni

doi:10.1038/s41598-020-70201-z

Matheus Sampaio C Barreto, Evert J Elzinga + Show 1 more

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https://doi.org/10.1038/s41598-020-70201-z

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Abstract

Proteins are of ubiquitous interest in the Life Sciences but are of interest in the Geosciences as well because of the significant role these compounds play in the biogeochemical cycling of trace and nutrient elements. Structural changes resulting from the adsorption of proteins onto mineral surfaces may alter protein biological function and other environmental interactions. Iron oxides are major sinks of a range of environmental elements including organic compounds. In this study, the adsorption of the broadly studied model protein BSA onto the hematite mineral surface was characterized as a function of pH, ionic strength, and BSA concentration using in-situ Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy. BSA lost the α-helix and gain β-sheets in the secondary structure during adsorption on hematite. BSA adsorption was maximum at pH 5, a value close to the BSA isoelectric point (~ pH 5), and lower at pH 4 and pH 7. Increasing ionic strength decreased to total BSA adsorption. Two-dimensional correlation spectroscopy analysis of the ATR-FTIR spectra revealed that higher initial BSA concentration and the consequent higher BSA surface loading enhanced BSA adsorption by protein–protein interaction, which less ordered structures changes into more compact forms decrease, hence compacting the structural arrangement and could promoting multilayers/aggregation formation on the mineral surface. The activity of enzymes following adsorption on mineral surfaces requires further study.

Highlights

Interest in the Geosciences regarding protein behavior is the result of its role in the biogeochemical cycling of trace and nutrient elements
Secondary structure can be determined by IR spectroscopy, because structural arrangements in the protein chain are associated with specific vibrational bands[38,39,40,41,42,43,44,45,46]
ATR-Fourier Transform Infrared (FTIR) spectroscopic measurements demonstrate that Bovine serum albumin (BSA) underwent dynamic change of the conformation of adsorbed protein on the hematite surface in response to environmental variables as: initial protein concentration on solution, ionic strength and value of pH medium

Summary

Introduction

Interest in the Geosciences regarding protein behavior is the result of its role in the biogeochemical cycling of trace and nutrient elements. As enzymes, are subject to adsorption onto the surfaces of the mineral fraction This should affect the protein’s biological functions[33,34,35], as its functionality is determined by protein chemical and physical properties, which in turn are determined by the interactions between its amino acid residues in three dimensional s pace[36]. Besides IR, other techniques used to determine structure include X-ray c rystallography[47] and UV-circular d ichroism[46,48,49,50] Environmental variables such as the nature of the adsorbent surface (e.g. hydrophobicity) and protein properties (e.g. molecular weight, amino-acids composition and sequence), medium pH, ionic strength, others ions/ compounds in to the system are understood to influence these protein adsorption forces, which guides to a complex organo-mineral system with simultaneously kinetic, structural, and thermodynamic controls. Iron oxides are major sinks to several environmental compounds including organic[61] and inorganic pollutants[62] and control the availability of plant nutrients in soils[63]

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