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

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.

Supercharged Protein Nanosheets for Cell Expansion on Bioemulsions

“… 8 , 31 − 35 In contrast, αLA has a molecular weight of only 14 kDa and significantly different amino acid composition (36% homology with BSA, only 31% α-helix composition, Figure S4 ). 36 , 37 Hence, we propose that the smaller size and more disordered structure of αLA result in more classic tensioactive properties, without the formation of protein networks at liquid–liquid interfaces (perhaps associated with reduced denaturation upon adsorption), resulting in more fluid interfaces with lower interfacial storage moduli, compared to BSA and HSA. However, in the presence of the co-surfactant PFBC, the abundance of functionalizable residues (e.g., lysine, serine, tyrosine, and threonine) at the surface of the three types of albumins tested (see Figure S4 ) underpinned the formation of physical cross-links and the establishment of a more interconnected protein network, associated with an increase in interfacial elasticity ( Figures 1 F, S2 and S3 ).…”

“…8,31−35 In contrast, αLA has a molecular weight of only 14 kDa and significantly different amino acid composition (36% homology with BSA, only 31% α-helix composition, Figure S4). 36,37 Hence, we propose that the smaller size and more disordered structure of αLA result in more classic tensioactive properties, without the formation of protein networks at liquid−liquid interfaces (perhaps associated with reduced denaturation upon adsorption), resulting in more fluid interfaces with lower interfacial storage moduli, compared to BSA and HSA.…”

Supercharged Protein Nanosheets for Cell Expansion on Bioemulsions

“…The comparable mechanical properties of BSA and HSA nanosheets may be anticipated from the similarity of their molecular weight (66 and 64 kDa, respectively), amino acid composition (76 % homology) and isoelectric point (4.5 and 4.7, with zeta potentials of −20 and −21 mV, respectively; Supplementary Figure S4) [31][8][32] [33] [34][35] . In contrast, αLA has a molecular weight of only 14 kDa and significantly different amino acid composition (36 % homology with BSA, only 31 % α-helix composition, Supplementary Figure S4) [36][37] . Hence, we propose that the smaller size and more disordered structure of αLA results in more classic tensio-active properties, without the formation of protein networks at liquid-liquid interfaces (perhaps associated with reduced denaturation upon adsorption), resulting in more fluid interfaces with lower interfacial storage moduli, compared to BSA and HSA.…”

One-Pot Assembly of Drug-Eluting Silk Coatings with Applications for Nerve Regeneration

“…All samples were composed of nanoscale globular aggregates with relatively homogeneous distributions of globule diameters, 55 ± 8 nm (unloaded SF-only), 52 ± 9 nm (ALAC loaded), 52 ± 7 nm (LYS loaded), and 58 ± 7 nm (BLAC loaded). 60 3.6 32 ± 2 34.2−34.9 25−30 BLAC 61 5.5 30 ± 3 32.6−33.0 14−17 LYS 62 3. As described in the Materials and Methods section, estimated volume contributions of the model proteins in the coassembled SF globules incorporated into the coatings were calculated utilizing the hydrodynamic diameter of SF aggregates measured via DLS in the coating solution, and hydrodynamic diameters of model proteins were taken from the literature.…”