Cationized bovine serum albumin as gene carrier: Influence of specific secondary structure on DNA complexibility and gene transfection

In this research, BSA, one of the natural rigid globular proteins with ca. 51% of α-helix secondary structure, was utilized to prepare cationized BSA (cBSA) as gene carrier. Tetraethylenepentamine (TEPA) or polyethylenimine (PEI 1800 ) was grafted to BSA with different grafting levels. Based on the circular dichoism (CD) spectra, all cBSA remained α-helical structure to some degree. This was exciting to endow cBSA with quite different DNA complexibility and cellular biology behavior from the random coiled and flexible polycations such as PEI and poly- l- lysine (PLL). Strangely, the DNA condensability decreased with the increment of TEPA or PEI 1800 grafting level. Also, the cBSA could condense DNA effectively to form irregular nanoparticles around 50–200   nm above N/P ratio of 10. On account of the excellent hydration of BSA, the cBSA/DNA complexes revealed good colloidal stability under physiological salt condition. Cell culture experiments indicated this BSA-based gene carrier possessed good cellular compatibility. Surprisingly, cBSA/DNA complexes could be uptaken excellently by up to 90% cells. This might be owing to the agitation effect of α-helical structure and the positive potential of these complexes. BSA-PEI 1800 /DNA complexes with quick endosome escape even had transfection efficiency as high as PEI 25k /DNA complexes. Overall, this paper provided us the potential of cBSA as gene carrier and might have some instructions in the design of protein-based gene delivery system.