RAMAN-SPECTROSCOPIC STUDIES OF THE ANHYDROUS COMPLEXES OF AVIDIN AND STREPTAVIDIN WITH BIOTIN

FT Raman spectra of avidin, streptavidin, and of the two anhydrous bio tin complexes were obtained by excitation in near infrared (NIR). As f ar as avidin and the avidin-biotin complex are concerned, the excitati on in NIR did not change the main features of the spectra compared wit h those previously obtained by visible excitation. However, the intens ity of Trp bands did not change due to the formation of the complex wh en excited by NIR excitation, whereas an intensity increase was observ ed by 514 nm excitation. The percentages of secondary structure of the two proteins and the biotin complexes were obtained from the Raman sp ectra. The vibrational results indicate that as a consequence of the i nteraction with biotin, the percentages of beta-sheet conformation of the proteins decrease whereas the percentages of alpha-helix conformat ion increase. The observed changes of the conformation of streptavidin induced by biotin interaction are comparable with those obtained with avidin; this fact confirms that the type of the binding should be sim ilar for the two molecules. Moreover, as a result of the biotin bindin g, the hydrophobicity of the environment of the Trp residues of strept avidin slightly increases according to the increase in intensity of th e 1360 cm(-1) component. This result could suggest that the streptavid in-biotin complex is stabilized mainly by hydrophobic interactions. (C ) 1996 John Wiley & Sons, Inc.