BOAR SPERM PROACROSIN INFRARED INVESTIGATION - SECONDARY STRUCTURE-ANALYSIS AFTER AUTOACTIVATION AND SURAMIN BINDING

Fourier transform infrared spectroscopy was used to investigate the se condary structure of boar sperm proacrosin at p(2)H 5.5, to determine the structural changes following protein autoactivation to beta-acrosi n at p(2)H 8.0 and to study the effect of suramin binding on the prote in secondary structure. At p(2)H 5.5, proacrosin contents of alpha-hel ix, beta-sheet, turns, and unordered structures were estimated to be 9 , 49-51, 16-18, and 24%, respectively. At p(2)H 8.0, the protein was p artially insoluble; spectral analysis of the soluble fraction, which c ontained beta-acrosin, showed an overall secondary structure quite sim ilar to that of proacrosin at p(2)H 5.5. However, p(2)H 8.0 spectra of the soluble protein (beta-acrosin), together with the thermal denatur ation experiments, indicated that, compared to proacrosin, beta-acrosi n showed an increased content of beta-sheets exposed to the solvent as well as a different tertiary structure. Proacrosin/suramin interactio n at p(2)H 5.5 resulted in the formation of soluble and insoluble comp lexes and the relevant infrared spectra showed only minor differences with respect to the native proacrosin. However, the thermal denaturati on curves revealed that suramin induced a destabilization of proacrosi n structure. The data also indicated that suramin could modify the int eraction characteristics of proacrosin aspartyl and glutamyl residues, thus suggesting competition of suramin with these two residues for io nic interactions. (C) 1996 Academic Press, Inc.