RAMAN-SPECTROSCOPIC STUDY OF THE AVIDIN-BIOTIN COMPLEX

Raman spectra of avidin, biotin and the avidin-biotin complex were rec orded. The percentages of secondary structure of avidin and the avidin -biotin complex were obtained from the Raman spectra. The vibrational results indicate that, as a consequence of the interaction of avidin w ith biotin, the beta-sheet conformation percentage decreases and the a lpha-helical conformation percentage increases. Moreover, the interact ion of avidin with biotin is also able to change slightly the tertiary structure of the protein. In fact, as a consequence of the binding of biotin, the hydrophobicity of the environment of Trp increases slight ly according to the intensity increase of the 1360 cm(-1) component Th e intensity of all bands attributable to Trp residues increases with b iotin binding, indicating that Trp is directly involved in the interac tion. These results are in agreement with the results of UV measuremen ts which indicate a red shift of the avidin Trp absorption bands as a consequence of the binding to biotin.