Browsing by Author "Raynova Y."

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    SYNTHESIS AND STABILITY OF A RAPANA THOMASIANA HEMOCYANIN CONJUGATED WITH VITAMIN B9
    (2020-01-01) Guncheva M.; Raynova Y.; Idakieva K.; Todinova S.; Yancheva D.
    This is the first report on the synthesis of vitamin B9-Rapana thomasiana hemocyanin conjugates (vit. B9-RtH). Proteins modified with 25 and 150 vitamin B9 residues аre obtained in a coupling reaction between N-hydroxysuccinimide-activated γ -carboxylic groups of vitamin B9 and the amino-groups of N-terminal amino acids and lysines comprising the protein. ATR-FTIR spectroscopy is applied to monitor the changes of the secondary structure upon the modification. The comparison of the secondary structure of the native and the vitamin B9-conjugated RtHs shows that the modification results in an increase of the β-structures in a favor of α-helices and coiled structures. The therrmal stability of the novel preparations is evaluated by differential scanning calorimetry (DSC). Despite the serious changes of the conformation, the vit.-B9-RtH conjugates are characterized by a high thermal stability. It is assumed that the changes of the DSC profiles are due to alternative protein-protein interactions, e.g H-bonding, stacking or hydrophobic interactions with vitamin B9 moieties that are possible in the modified RtH molecules
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    Thermal stability and secondary structure of feruloylated Rapana thomasiana hemocyanin
    (2019-11-01) Guncheva M.; Todinova S.; Yancheva D.; Raynova Y.; Idakieva K.
    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 α-helices and coiled structures in favor of the β-structures, and no aggregation in comparison with the native RtH.