Ig-like Domain in Endoglucanase Cel9A from Alicyclobacillus acidocaldarius Makes Dependent the Enzyme Stability on Calcium
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Endoglucanase Cel9A from Alicyclobacillus acidocaldarius (AaCel9A) has an Ig-like domain and the enzyme stability is dependent to calcium. In this study the effect of calcium on the structure and stability of the wild-type enzyme and the truncated form (the wild-type enzyme without Ig-like domain, AaCel9AΔN) was investigated. Fluorescence quenching results indicated that calcium increased and decreased the rigidity of the wild-type and truncated enzymes, respectively. RMSF results indicated that AaCel9A has two flexible regions (regions A and B) and deleting the Ig-like domain increased the truncated enzyme stability by decreasing the flexibility of region B probably through increasing the hydrogen bonds. Calcium contact map analysis showed that deleting the Ig-like domain decreased the calcium contacting residues and their calcium binding affinities, especially, in region B which has a role in calcium binding site in AaCel9A. Metal depletion and activity recovering as well as stability results showed that the structure and stability of the wild-type and truncated enzymes are completely dependent on and independent of calcium, respectively. Finally, one can conclude that the deletion of Ig-like domain makes AaCel9AΔN independent of calcium via decreasing the flexibility of region B through increasing the hydrogen bonds. This suggests a new role for the Ig-like domain which makes AaCel9A structure dependent on calcium.
KeywordsEndoglucanase Cel9A Ig-like domain Molecular dynamics simulation Calcium
Alicyclobacillus acidocaldarius endoglucanase Cel9A
AaCel9A without Ig-like domain
Carbohydrate binding domain
Radial distribution function
The authors express their gratitude to the research council of Azarbaijan Shahid Madani University for the financial support during the course of this project.
Compliance with Ethical Standards
Conflict of interest
The authors declare that there are no conflicts of interest.
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