Study of conformational changes in glucoamylase of Aspergillus awamori nakazawa in presence of denaturants through CD-spectroscopy

In present study, changes in the pattern or motifs of secondary structures of glucoamylase from Aspergillus awamori nakazawa in the presence of denaturants such as urea, guanidine-HCl (Gdn-HCl), and at different pH, were studied through CD-spectroscopy. It was observed that in native state glucoamylase entirely comprised of β-sheets. CD-spectra of glucoamylase in the presence of 6 M urea lost its spectral regular characteristic; and ellipticity became zero between 207 and 218 nm. With 0.5 M urea concentration glucoamylase showed approximately double negative ellipticity between 207 and 218 nm than the control, which indicates increase in β-sheets and decrease in random coil contents. But higher concentration of urea (⩾6 M) and Gdn-HCl (⩾3 M) completely unfold the enzyme. At lower concentration (0.1 M) of Gdn-HCl negative peak got shifted from 208 to 219 nm to a very sharp peak at 198 nm with lower intensity than the control. It was also observed that glucoamylase posses higher β-sheet in acidic media than in basic media. Glucoamylase remains active in a broad range of pH (3.0–11.0) and maximum activity was observed at pH 4.5. Activity of glucoamylase does not vary too much between pH 5.5 and 9.0. Conformational changes during wide range of pH were supported with its activity coincided.