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Effects of Salt and Ligand Concentrations on the Thermal Unfolding and Refolding of Halophilic Starch-Binding Domain from Kocuria varians α-Amylase

[ Vol. 19 , Issue. 3 ]


Rui Yamaguchi, Tsutomu Arakawa, Hiroko Tokunaga, Matsujiro Ishibashi and Masao Tokunaga   Pages 326 - 332 ( 7 )


The starch binding domain of α-amlylase from moderate halophile was expressed in E. coli with His tag (His- SBD12) and characterized for its halophilic properties. His-SBD12 was stable up to 35°C and showed binding activity, although at reduced level, to amylose even in the absence of NaCl. Both NaCl and specific ligands exhibited insignificant influence on the secondary structure of His-SBD12, but showed significant stabilization effects against thermal unfolding concentration-dependently, showing its halophilic properties. NaCl increased thermal stability of His-SBD12 by 4°C at 0.2 M and 15°C at 2 M, and enhanced refolding rate by ˜7-fold at 0.2 M and ˜170-fold at 2 M. Its specific ligands, β- cyclodextrin (at 3 mM) and maltose (at 470 mM), also stabilized the protein by 11° C, most likely reflecting affinity difference between these two ligands. However, they showed marginal effects on refolding rate. These observations suggest that although binding of NaCl and specific ligands to the native structure can explain their stabilization effects on His- SBD12, it is not a sole factor for modulating their effects on folding of His-SBD12.


Halophilic, starch binding domain, thermal unfolding, refolding, salt concentration, β-cyclodextrin, reversibility, N-terminal hexa-His-tag, SDS-PAGE, Chromohalobacter β-lactamase


Applied and Molecular Microbiology, Faculty of Agriculture, Kagoshima University, 1-21-24 Korimoto, Kagoshima 890-0065, Japan.

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