Grafting of Aliphatic and Aromatic Probes on Rapeseed 2S and 12S Proteins: Influence on Their Structural and Physicochemical Properties

Abstract

Lysyl residues of rapeseed napin (2S) and cruciferin (12S) were acylated and sulfamidated by means of anhydrides and sulfonyl chlorides, respectively. The secondary and tertiary structures as well as the surface hydrophobicity of the modified proteins were studied using circular dichroism, intrinsic fluorescence, and binding of anilinonaphthalenesulfonic acid. The results showed clearly that grafting of hydrophobic chains induced different structural modifications and surface hydrophobicities on the monomeric (2S) and on the hexameric (12S) proteins. Thus, the original structure of the 2S modified protein seemed to be preserved. Therefore, the surface hydrophobicity increased proportionally with the number of groups grafted. Conversely, after modification, 12S was shown to be expanded. As a result, hydrophobic regions were exposed, leading to a much greater hydrophobization of the protein surface. Acylation and sulfamidation appeared, therefore, to be good methods to hydrophobize efficiently the surface of the two proteins and thus might probably induce new functional properties.

Effect of maleylation on physicochemical and functional properties of rapeseed protein isolate

“…Successive maleylation caused a drastic loss in α-helix content with a concomitant rise in β-structures and random coils (Table 1). These results are in good agreement with published data on modified 12S and 2S rapeseed proteins (Gerbanowski et al 1999). Achouri and Zhang (2001) also found a pronounced tendency of soy protein hydrolysates towards randomness with increasing modification level.…”

“…This can be deduced from the conformational perturbations like partial unfolding, progressive dissociation or expansion of the native oligomeric structure (Matemu et al 2011), a conclusion in accordance with the greater random coil feature and dissociated protein subunits as suggested by FTIR and GPC results, respectively. Some refolding mechanism or protein aggregation through hydrophobic interactions might have occurred in 0.8MA leading to less exposure of Trp groups to the polar solvent (Gerbanowski et al 1999), as evident from the blue shift of its λ max (Fig. 3).…”

“…For the above-stated reason, efforts have been made to improve the functionalities of oilseed proteins, and probably, the best documented of these efforts involve chemical and enzymatic modifications. Numerous investigations through chemical modification (succinylation, acetylation, phosphorylation and sulfamidation) or enzymatic modification of rapeseed proteins have been undertaken (Gruener and Ismond 1997;Gerbanowski et al 1999;Schwenke et al 2000;Sánchez-Vioque et al 2004); however, proteolysates from the latter method are frequently bitter and lacks satisfactory foam/emulsion stability (Franzen and Kinsella 1976). Moreover, there are indications that all peptides do not contribute equally to the reported biological activities and thus the purification of active peptides is needed (Aachary and Thiyam 2012), making it a cumbersome and expensive technique.…”

Reactions of Plant Phenolics with Food Proteins and Enzymes under Special Consideration of Covalent Bonds

“…Such interactions can be confirmed as shown by the progressive decrease in the amount of free tryptophan (Suryaprakash et al, 2000;Rawel et al, 2002b). From the progressive quenching and the red shift observed in the maximum fluorescence emission of derivatized BSA, it can be deduced that conformational changes induced by the modification lead to a further exposure of tryptophan residues to the polar solvent (Jackman & Yada, 1989;Gerbanowski et al, 1999). Similar observations were also recorded for the reaction of ␤-lactoglobulin with quercetin and rutin .…”

“…These changes in spectra highlight some conformational changes induced by the derivatization, affecting the tertiary structure and perturbing the initial conformation of the protein. Chemical modification (acylation and sulfamidation) also produces a similar destructuring of proteins (Gerbanowski et al, 1999). …”