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.
Highlights
Introduction αAmylase (EC 3.2.1.1; 1,4-α-D glucan glucanohydrolase), catalyzing random endohydrolysis of α-1,4 glycosidic linkages in starch and related carbohydrates with retention of α-anomeric configuration in the products [1, 2], has been a commercially significant and robust enzymePLOS ONE | DOI:10.1371/journal.pone.0129203 June 8, 2015Unfolding Pathways of Wheat α-Amylase under Different Environments analysis, decision to publish, or preparation of the manuscript
Limited mechanistic understanding of the innate ability of proteins to fold into their native, functional form from their one dimensional unit, have plagued researchers for past several decades, several theories have emerged about this remarkable biochemical event based on studies of small, monomeric, single-domain proteins [28,29,30]
The conformational transition of such proteins is given by a specific trajectory or bundle of trajectories on energy landscape being dictated by the primary sequence as well as the environment surrounding it [34]
Summary
Introduction αAmylase (EC 3.2.1.1; 1,4-α-D glucan glucanohydrolase), catalyzing random endohydrolysis of α-1,4 glycosidic linkages in starch and related carbohydrates with retention of α-anomeric configuration in the products [1, 2], has been a commercially significant and robust enzymePLOS ONE | DOI:10.1371/journal.pone.0129203 June 8, 2015Unfolding Pathways of Wheat α-Amylase under Different Environments analysis, decision to publish, or preparation of the manuscript. Amylase (EC 3.2.1.1; 1,4-α-D glucan glucanohydrolase), catalyzing random endohydrolysis of α-1,4 glycosidic linkages in starch and related carbohydrates with retention of α-anomeric configuration in the products [1, 2], has been a commercially significant and robust enzyme. Unfolding Pathways of Wheat α-Amylase under Different Environments analysis, decision to publish, or preparation of the manuscript
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