The 1,4-α-glucan branching enzymes (GBEs; EC 2.4.1.18) play an irreplaceable role in controlling of frequency and position of branch points in starch, which are capable of changing the structural and physical properties of starch and glycogen. The GBE in our research is from Geobacillus thermoglucosidans STB02 (GBEGt) that belongs to thermophilic enzymes, whose characteristics of this enzyme may be associated with more numerous charged residues on surface than those of mesophilic enzymes. Comparison of the amino acid sequences and three-dimensional structures of mesophilic and thermophilic GBEs shows that GBEGt has a 26 amino-acid C-terminal extension consisting of 50% charged residues, and that their 3-dimensional structure is flexible. Removal of this C-terminal extension (GBEGtΔC) eliminated the metal ion dependence of GBEGt, increasing its stability and EDTA tolerance. A solubility and stability analysis showed that GBEGtΔC was more stable than GBEGt. The circular dichroism and intrinsic fluorescence spectra of GBEGt and GBEGtΔC revealed that the thermostability of GBEGtΔC was greater than GBEGt. The higher stability of GBEGtΔC without added metal ions may result from an alteration of aggregate state introduced by the C-terminal truncation. The enhanced performance of this truncation makes GBEGtΔC a candidate for use in metal ion free food processing and, therefore, much more suitable than GBEGt for the industrial production of food-grade modified starch.

C-terminal truncation decreases the metal ion dependence and improves stability of a thermophilic 1,4-α-glucan branching enzyme

256th National Meeting (2018)

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