Anahita Khammari - Department of Biophysics, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
Mostafa Shourian - Department of Biology, Faculty of Sciences, University of Guilan, Rasht, Iran
Seyed Shahriar Arab - Department of Biophysics, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran.
Leila Karami - Department of Cell and Molecular Biology, Faculty of Biological Sciences, Kharazmi University, Tehran, Iran.

Anti-Hepatitis B antibody (HB-Ab) is an important antibody with enormous medical diagnostic, and biosensing applications. Thus, any improvement in the applicability of the antibody is potentially interesting. In this study, we investigated the covalent attachment effects of streptavidin (STP) to anti-Hepatitis B antibody (HB-Ab) as a novel conjugated protein. The attachment of STP to HB-Ab can amplify the immunosensor signal due to STP multi-binding sites. When STP is covalently attached to the Fc region of anti-HBsAg antibody, it can provide one, two, three or even four different binding sites for the biotin. The covalent attachment of STP (carboxylic acid) to the surface-exposed Lys residues successfully improves attachment properties of HB-Ab. Here we investigated structural and functional consequences of this modification, which accessible charged lysines (Lys-121of each subunit) to the streptavidin glutamate (Glu-417) residues. Fluorescence and circular dichroism investigations suggest that the modified HB-Ab benefits from attachment to STP as compared to the native one. For comparing the all conformational changes of streptavidin while attachment to antibody and affinity change of streptavidin to biotin were carried out by molecular dynamic (50 nano-second). To obtain the result of molecular dynamic, first the streptavidin attached to antibody system build, after that the structure and affinity was compared by reference system. It is known that the major conformational change of the protein associated with biotin binding is the closure of the loop3-4, and the open-close transition process is beyond the time frame of standard molecular dynamic simulation. In summary, this modification produces a new derivative of HB-Ab with enhanced attacment properties, and stability for biotechnological applications.

Anti-Hepatitis B antibody; streptavidin; covalent attachment; molecular dynamic simulation