Sandbox Reserved 338: Difference between revisions
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TreX is an oligomer, as it exists in a dimeric state and a tetrameric state, both of which exhibit different enzymatic activities. All subunits are identical, where the monomer contains a total of 612 amino acids <ref name="Woo" />. The polypeptide folds into two secondary structures, a β-sandwhich in the N terminal region, comprised of six β-strands and a (β/α)8 – barrel motif in the central domain, comprised of eight parallel α-strands which encircle eight parallel β-strands. The sequence composition of the TreX monomer exhibits a high degree of homology to the isoamylase debranching enzyme of Pseudomona, however the TreX monomer mainly deviates from this similarity in its substrate binding groove and the absence of a calcium ion ligand <ref name="Woo" />. | TreX is an oligomer, as it exists in a dimeric state and a tetrameric state, both of which exhibit different enzymatic activities. All subunits are identical, where the monomer contains a total of 612 amino acids <ref name="Woo" />. The polypeptide folds into two secondary structures, a β-sandwhich in the N terminal region, comprised of six β-strands and a (β/α)8 – barrel motif in the central domain, comprised of eight parallel α-strands which encircle eight parallel β-strands. The sequence composition of the TreX monomer exhibits a high degree of homology to the isoamylase debranching enzyme of Pseudomona, however the TreX monomer mainly deviates from this similarity in its substrate binding groove and the absence of a calcium ion ligand <ref name="Woo" />. | ||
In the dimeric form, the individual subunits are adjacent to each other, where both of the active sites face the same side <ref name="Woo" />. In the tetrameric form, two of the associated dimers face each other so as to position the substrate binding sites to the inside of the tetramer, facing each other with a slight offset <ref name="Woo" />. Unlike other GDEs, TreX portrays different enzymatic activities in correlation to its oligomeric state. The dimeric form is predominantly associated with α-1,6-glycosidase, whereas the tetratmeic form is associated with α-1,4-transferase activity <ref name="Woo" />. | In the dimeric form, the individual subunits are adjacent to each other, where both of the active sites face the same side <ref name="Woo" />. In the tetrameric form, two of the associated dimers face each other so as to position the substrate binding sites to the inside of the tetramer, facing each other with a slight offset <ref name="Woo" />. Unlike other GDEs, TreX portrays different enzymatic activities in correlation to its oligomeric state. The dimeric form is predominantly associated with α-1,6-glycosidase, whereas the tetratmeic form is associated with α-1,4-transferase activity <ref name="Woo" />. | ||
The active site of TreX dimer contains three important catalytic residues (Asp<sup>363</sup>, Glu<sup>399</sup>, and Asp<sup>471</sup>) situated at the bottom of the active site cleft. The dimer active site exhibits a buried interface of 1523 Å, and a total of 6 subsites, where subsite 1 contains the NYWDYDP motif important which facilitates substrate interactions of the glucose rings. One of the interesting features which separate TreX from similar isoamylases and pullulanases, it the presence of a helix α4 loop (aa 228-238) situated at the bottom of the substrate binding groove. It is suggested that this helix α4 loop may provide a stable binding region for branched substrates with long chains, and therefore increase the activity of this GDE <ref name="Woo" />. | The active site of TreX dimer contains three important catalytic residues (Asp<sup>363</sup>, Glu<sup>399</sup>, and Asp<sup>471</sup>) situated at the bottom of the active site cleft. The dimer active site exhibits a buried interface of 1523 Å, and a total of 6 subsites, where subsite 1 contains the NYWDYDP motif important which facilitates substrate interactions of the glucose rings. One of the interesting features which separate TreX from similar isoamylases and pullulanases, it the presence of a helix α4 loop (aa 228-238) situated at the bottom of the substrate binding groove. It is suggested that this helix α4 loop may provide a stable binding region for branched substrates with long chains, and therefore increase the activity of this GDE <ref name="Woo" />. | ||
