Effect of temperature and pH on the secondary structure and processes of oligomerization of 19 kDa alpha-zein

Highly hydrophobic protein Z19 zein shows a tendency towards oligomerization. The role of temperature and pH on the oligomerization process was studied monitoring the secondary structure content and the appearance of aggregates by Circular Dichroism Spectroscopy (CD) and Dinamic Light Scattering (DLS). Z19 zein suffers irreversible thermal denaturalization, as demonstrated by far-UV CD measurements. DLS data indicate that this denaturalization is accompanied by oligomerization processes which are strongly dependent on temperature. The aggregates that appear when the sample is heated maintain a certain amount of their native structure. Oligomers, showing high stability to temperature changes and other denaturing conditions with molecular weights of 45, 66 kDa and higher, were detected by SDS-PAGE. The secondary structure strongly depends on pH. Thus, at pH above pI (6.8), all the protein structure is in alpha helix. The formation of disulfide bonds plays an important role in the aggregation process, since most of the sulfhydryls in the protein (97.52%) form disulfide bonds and only 2.47% of them are free and superficially exposed. The sensitivity towards thermal denaturalization is also affected by pH rises.