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![[Figure 1]](jc5055fig1mag.jpg)
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Figure 1
Overview of sequence signatures, structure and model substrates of GEs in CE15. (a) Sequence signatures for the CE15-A and CE15-B subgroups as described previously (Ernst et al., 2020  ) and the corresponding sequence in LfCE15C, with significant residues differing from the CE15-B signature circled in red. The four signature regions are separated by dashes, while additional residues that are not shown within the regions are indicated by dots with the number of residues in parentheses (asterisks indicate that the number is variable). The location on secondary-structure elements is indicated (see below) and residues expected to directly contact the substrate are shaded. Fully or almost fully conserved residues within the subgroup are in black, while semi-conserved residues are in white. Catalytic residues are underlined and include the oxyanion-hole Arg in addition to the classical triad Ser, His and Glu/Asp. The catalytic acid differs in the two subgroups. The corresponding sequence in the bacterial OtCE15A is shown, which contains functional acid residues at both canonical and noncanonical positions. Coloured boxes correspond to the colours of the secondary-structure elements in (b). The correspondence of residues is based on structural alignment. (b) Selected structural elements of GEs illustrated with the structure of OtCE15A (PDB code 6t0i). β5–β8 denote the main β-strands numbered according to the core ABH numbering. αL is an α-helix-containing loop involved in substrate binding. The semitransparent cyan surface shows the position of the product XU2X [22-(4-O-methyl-α-D-glucuronyl)-xylotriose, also referred to as XUX]. (c) Overview of GE and other CE model substrates tested in this work. In BnzGlcA and MeGlcA, R2 is H and R1 is a benzyl or methyl group, respectively. In 4-O-Me-MeGlcA, both R1 and R2 are methyl groups. |
![[Figure 1]](jc5055fig1.jpg)
 | STRUCTURAL BIOLOGY |
ISSN: 2059-7983
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