A Raman study of the interactions of streptavidin with biotin and biotinyl derivatives

Raman spectra of Streptavidin and its complexes with some Biotin and Biotinyl derivatives were recorded. The b-sheet percentages of the secondary structure of Streptavidin, calculated by two different methods, decreased as a consequence of the interaction with Biotin derivatives. The Biotinyl derivatives did not significantly change the spectral features of the protein and, consequently, the secondary structure. The difference in behaviour between Biotin and Biotinyl derivatives, is owing to the absence of one hydrogen bond formed between the ligand and some aminoacid residues of the protein (Asn and Ser). The modification in the secondary structure should be ascribed to the surface loop which binds the strands of the b-barrel and not to the b-sheet strands which form the active site binding of the protein