Formation of molten globule-like state during acid denaturation of Aspergillus niger glucoamylase

详细信息    查看全文

• 作者：Mohammed Suleiman Zaroog ; Saad Tayyab ; ^{saadtayyab2004@yahoo.com}
• 关键词：ANS ; 1-anilinonaphthalene-8-sulfonic acid ; CD ; circular dichroism ; GdnHCl ; guanidine hydrochloride ; MRE ; mean residue ellipticity ; NATA ; N-acetyl-l-tryptophanamide ; SBD ; starch binding domain ; Trp ; tryptophan ; Tyr ; tyrosine
• 刊名：Process Biochemistry
• 出版年：2012
• 出版时间：May, 2012
• 年：2012
• 卷：47
• 期：5
• 页码：775-784
• 全文大小：653 K

文摘

Acid denaturation of Aspergillus niger glucoamylase was studied using different conformational probes. Both far-UV CD spectral signal (MRE_222 nm) and tryptophan fluorescence remained unchanged in the pH range, 7.0-3.0 but decreased significantly below pH 3.0, whereas ANS fluorescence showed a marked increase below pH 1.5. Maximal changes in MRE_222 nm and ANS fluorescence were noticed at pH 1.0. Acid-denatured state of glucoamylase at pH 1.0 retained a significant amount of secondary structure as reflected from far-UV CD spectra but showed a deformed tertiary structure with significant exposure of nonpolar groups as well as tryptophan residues as revealed by increased ANS fluorescence, decreased tryptophan fluorescence and three-dimensional fluorescence spectral signals and increase in K_sv value in acrylamide quenching experiments. Acid-denatured state showed no significant variation in the CD spectral signal throughout the temperature range, 0-100 ¡ãC. However, a late cooperative transition was observed upon GdnHCl treatment, compared to the native enzyme. All these results suggested that the acid-denatured state of glucoamylase at pH 1.0 represented the molten globule-like state.