Thermal stability and secondary structure of feruloylated Rapana thomasiana hemocyanin

This is the first report on the conjugation of a hemocyanin from Rapana thomasiana (RtH) with ferulic acid, which itself exhibits an immunostimulatory activity. In a two-step reaction, 20 to 180 ferulic acid residues were covalently linked to one molecule RtH. The effect of modification of RtH with ferulic acid on the thermal unfolding was evaluated using differential scanning calorimetry (DSC). The DSC curves of the feruloylated-RtHs characterize with an asymmetric shape, which is an indication for the existence of more than one structural unit in the analyzed samples. The protein thermal stability is not affected by the modification; however, the profiles of the DSC curves of the feruloylated-RtH and the native RtH differ, which implies the reorganization in the protein molecule and is in correlation with the secondary structure analyses. The conformational changes in the RtH molecules that are due to the feruloylation were followed in the Amide I region (1600-1700 cm(-1)) of the ATR-FTIR spectra. In all prepared samples, we observed a rearrangement in protein molecule, decrease in alpha-helices and coiled structures in favor of the beta-structures, and no aggregation in comparison with the native RtH.