7zvo

</td></tr><tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=ALA:ALANINE'>ALA</scene>, <scene name='pdbligand=BME:BETA-MERCAPTOETHANOL'>BME</scene>, <scene name='pdbligand=CA:CALCIUM+ION'>CA</scene>, <scene name='pdbligand=CL:CHLORIDE+ION'>CL</scene>, <scene name='pdbligand=MPD:(4S)-2-METHYL-2,4-PENTANEDIOL'>MPD</scene>, <scene name='pdbligand=SER:SERINE'>SER</scene></td></tr>

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== Publication Abstract from PubMed ==

The Bacteroides thetaiotaomicron has developed a consortium of enzymes capable of overcoming steric constraints and degrading, in a sequential manner, the complex rhamnogalacturonan II (RG-II) polysaccharide. BT0996 protein acts in the initial stages of the RG-II depolymerisation, where its two catalytic modules remove the terminal monosaccharides from RG-II side chains A and B. BT0996 is modular and has three putative carbohydrate-binding modules (CBMs) for which the roles in the RG-II degradation are unknown. Here, we present the characterisation of the module at the C-terminal domain, which we designated BT0996-C. The high-resolution structure obtained by X-ray crystallography reveals that the protein displays a typical beta-sandwich fold with structural similarity to CBMs assigned to families 6 and 35. The distinctive features are: 1) the presence of several charged residues at the BT0996-C surface creating a large, broad positive lysine-rich patch that encompasses the putative binding site; and 2) the absence of the highly conserved binding-site signatures observed in CBMs from families 6 and 35, such as region A tryptophan and region C asparagine. These findings hint at a binding mode of BT0996-C not yet observed in its homologues. In line with this, carbohydrate microarrays and microscale thermophoresis show the ability of BT0996-C to bind alpha1-4-linked polygalacturonic acid, and that electrostatic interactions are essential for the recognition of the anionic polysaccharide. The results support the hypothesis that BT0996-C may have evolved to potentiate the action of BT0996 catalytic modules on the complex structure of RG-II by binding to the polygalacturonic acid backbone sequence.

 

== References ==