Structural Stability of Soybean (Glycine max) α-Amylase: Properties of the Unfolding Transition Studied with Fluorescence and CD Spectroscopy

Author(s): Arpana Kumari , Tobias Rosenkranz , Jorg Fitter , Arvind M. Kayastha .

Journal Name: Protein & Peptide Letters

Volume 18 , Issue 3 , 2011

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Abstract:

Stability and unfolding of mammalian and microbial α-amylases have been intensively investigated. However, there is only limited information available on the structural stability of plant α-amylases, namely of the two isoenzymes from barley AMY1 and AMY2, of the α-amylase from mung bean (Vigna radiata), and of the α-amylase from malted sorghum (Sorghum bicolor). We report here the stability of soybean α-amylase (GMA), against elevated temperatures and chemical denaturants (GndHCl) by employing circular dichroism and fluorescence spectroscopy. Since it is well-known that calcium ions play a crucial role for enzymatic activity and stability of α-amylases, we performed our studies with calcium bound and calcium free GMA. The thermal unfolding transition temperature decreased from 72 °C for calcium saturated samples to 57 °C for the case of calcium depleted GMA. Similarly, the GndHCl transition concentration was lowered from 0.70 M for calcium bound GMA to 0.41 M in the absence of calcium. Thermal unfolding of GMA is irreversible due to aggregation of the unfolded state. GMA unfolded in 6 M GndHCl shows high degree of reversibility after diluting the unfolded enzyme in native buffer containing 7 M glycerol. Furthermore, the refolded enzyme showed 93% of activity.

Keywords: α-Amylase, calcium binding, protecting osmolyte, protein aggregation, protein stability, unfolding kineticsα-Amylase, calcium binding, protecting osmolyte, protein aggregation, protein stability, unfolding kinetics

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Article Details

VOLUME: 18
ISSUE: 3
Year: 2011
Page: [253 - 260]
Pages: 8
DOI: 10.2174/092986611794578305
Price: $58

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