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Figure 6
Superposition of GH130 structures. Superposition of Uhgb_MP (GH130_2; red) with mannosyl-glucose phosphorylase (BfMGP) from B. fragilis NCTC 9343 (GH130_1; PDB entry 4kmi ; blue), and BACOVA_03624 from Bacteroides ovatus ATCC 8483 (GH130_NC; PDB entry 3qc2 ; green), illustrating the structural differences between GH130 subfamilies. The catalytic Asp104 is shown in the B conformation. With the exception of the BfMGP loop Thr42–Met68, which does not exist in the Uhgb_MP structure, the loops are numbered with respect to the Uhgb_MP sequence. The 11-­residue longer Gly121–Pro125 loop, which is specific to GH130_1, fills the entrance to the Uhgb_MP tunnel. In place of the Asp61–Arg65 loop, an extension is observed for GH130_NC, capping the catalytic site. These two loops, which are specific to GH130_1 and GH130_NC, respectively, may explain the inability of enzymes belonging to these subfamilies to phosphorolyze long substrates. Loop Asp171–Phe177 (the so-called `lid loop' in BfMGP) is shorter in GH130_NC enzymes than in GH130_1 and GH130_2, thus allowing access to the active site. In addition, in GH130_1 enzymes loop Asp171–Phe177 is very mobile because of the GSGGG motif located at its base, which is locked close to the catalytic site only when a substrate is bound, as shown for BfMGP structures. In contrast, in Uhgb_MP the loop is not so mobile and holds His174, which is conserved in GH130_2 and which has already been shown to be involved in the +1 subsite. The BfMGP loop Thr42–Met68 in contact with the N-terminal helix involved in oligomerization is completely absent in Uhgb_MP even when both proteins are assembled as homohexamers.

Journal logoBIOLOGICAL
ISSN: 1399-0047
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