Characterization of Conjugates between α-Lactalbumin and Benzyl Isothiocyanate—Effects on Molecular Structure and Proteolytic Stability

Jenny Spöttel,Sven Falke,Sascha Rohn,Johannes Brockelt

doi:10.3390/molecules26206247

Jenny Spöttel, Sven Falke + Show 2 more

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https://doi.org/10.3390/molecules26206247

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Abstract

In complex foods, bioactive secondary plant metabolites (SPM) can bind to food proteins. Especially when being covalently bound, such modifications can alter the structure and, thus, the functional and biological properties of the proteins. Additionally, the bioactivity of the SPM can be affected as well. Consequently, knowledge of the influence of chemical modifications on these properties is particularly important for food processing, food safety, and nutritional physiology. As a model, the molecular structure of conjugates between the bioactive metabolite benzyl isothiocyanate (BITC, a hydrolysis product of the glucosinolate glucotropaeolin) and the whey protein α-lactalbumin (α-LA) was investigated using circular dichroism spectroscopy, anilino-1-naphthalenesulfonic acid fluorescence, and dynamic light scattering. Free amino groups were determined before and after the BITC conjugation. Finally, mass spectrometric analysis of the BITC-α-LA protein hydrolysates was performed. As a result of the chemical modifications, a change in the secondary structure of α-LA and an increase in surface hydrophobicity and hydrodynamic radii were documented. BITC modification at the ε-amino group of certain lysine side chains inhibited tryptic hydrolysis. Furthermore, two BITC-modified amino acids were identified, located at two lysine side chains (K32 and K113) in the amino acid sequence of α-LA.

Highlights

It is well known that a balanced diet is crucial for maintaining good health [1]
The aim was to characterize the effect of benzyl isothiocyanate (BITC) conjugation on the amount of residual free amino groups of α-LA and to describe the degree of modification based on the change in spectrophotometrical absorbance
The restructuring was related to the increased surface hydrophobicity because the change of the secondary structure was assumed to expose more hydrophobic regions on the protein surface

Summary

Introduction

It is well known that a balanced diet is crucial for maintaining good health [1]. With the aim of increasing the consumption of vegetables with their health-promoting secondary plant metabolites, different recipes of traditional foods are improved with higher amounts of vegetables. Vegetables of the plant order Brassicales are associated with multiple health-promoting properties, largely due to the glucosinolates (GLS) or their hydrolysis products, in particular, isothiocyanates (ITC) [2–5]. Some studies reported anti-inflammatory, antibacterial, as well as antidiabetogenic effects, and it has even been shown that consumption of vegetables rich in GLS can reduce the risk of developing certain types of cancer [6–16]. Due to their high electrophilicity, ITC can interact with proteins in a diverse bunch of foods. They react with nucleophilic groups such as thiol and amino groups in proteins to form thiocarbamates and thioureas (Figure 1), and have a significant influence on various protein properties [5]

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