title: Heat, Acid and Chemically Induced Unfolding Pathways, Conformational Stability and Structure-Function Relationship in Wheat α-Amylase.
abstract: Wheat α-amylase, a multi-domain protein with immense industrial applications, belongs to α+β class of proteins with native molecular mass of 32 kDa. In the present study, the pathways leading to denaturation and the relevant unfolded states of this multi-domain, robust enzyme from wheat were discerned under the influence of temperature, pH and chemical denaturants. The structural and functional aspects along with thermodynamic parameters for α-amylase unfolding were probed and analyzed using fluorescence, circular dichroism and enzyme assay methods. The enzyme exhibited remarkable stability up to 70°C with tendency to aggregate at higher temperature. Acid induced unfolding was also incomplete with respect to the structural content of the enzyme. Strong ANS binding at pH 2.0 suggested the existence of a partially unfolded intermediate state. The enzyme was structurally and functionally stable in the pH range 4.0-9.0 with 88% recovery of hydrolytic activity. Careful examination of biophysical properties of intermediate states populated in urea and GdHCl induced denaturation suggests that α-amylase unfolding undergoes irreversible and non-coincidental cooperative transitions, as opposed to previous reports of two-state unfolding. Our investigation highlights several structural features of the enzyme in relation to its catalytic activity. Since, α-amylase has been comprehensively exploited for use in a range of starch-based industries, in addition to its physiological significance in plants and animals, knowledge regarding its stability and folding aspects will promote its biotechnological applications.
authors.affiliation: School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi, India.
authors.forename: Kritika
authors.initials: K
authors.lastname: Singh
authors.affiliation: Department of Biochemistry, University of Delhi South Campus, New Delhi, India.
authors.forename: Manish
authors.initials: M
authors.lastname: Shandilya
authors.affiliation: Department of Biochemistry, University of Delhi South Campus, New Delhi, India.
authors.forename: Suman
authors.initials: S
authors.lastname: Kundu
authors.affiliation: School of Biotechnology, Faculty of Science, Banaras Hindu University, Varanasi, India.
authors.forename: Arvind M
authors.initials: AM
authors.lastname: Kayastha
mesh_terms: D004789:Enzyme Activation; D004795:Enzyme Stability / Q000187:drug effects / Q000528:radiation effects; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D008958:Models, Molecular; D011487:Protein Conformation / Q000187:drug effects / Q000528:radiation effects; D011489:Protein Denaturation; D058767:Protein Unfolding / Q000187:drug effects / Q000528:radiation effects; D013329:Structure-Activity Relationship; D013816:Thermodynamics; D014908:Triticum / Q000201:enzymology*; D000516:alpha-Amylases / Q000737:chemistry* / Q000378:metabolism*
chemical_list: D000516:alpha-Amylases