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==Crystal structure of GH5_22 exo-beta-xylosidase from the seaweed-derived thermophile Geobacillus thermodenitrificans OS27==
<StructureSection load='9kua' size='340' side='right'caption='[[9kua]], [[Resolution|resolution]] 2.70&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[9kua]] is a 2 chain structure with sequence from [https://en.wikipedia.org/wiki/Geobacillus_thermodenitrificans Geobacillus thermodenitrificans]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=9KUA OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=9KUA FirstGlance]. <br>
</td></tr><tr id='method'><td class="sblockLbl"><b>[[Empirical_models|Method:]]</b></td><td class="sblockDat" id="methodDat">X-ray diffraction, [[Resolution|Resolution]] 2.7&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=FE:FE+(III)+ION'>FE</scene></td></tr>
<tr id='resources'><td class="sblockLbl"><b>Resources:</b></td><td class="sblockDat"><span class='plainlinks'>[https://proteopedia.org/fgij/fg.htm?mol=9kua FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=9kua OCA], [https://pdbe.org/9kua PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=9kua RCSB], [https://www.ebi.ac.uk/pdbsum/9kua PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=9kua ProSAT]</span></td></tr>
</table>
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== Publication Abstract from PubMed ==
Geobacillus thermodenitrificans OS27 is a seaweed-derived thermophile that harbors a GH5_22 gene (bxlA) that encodes for a glycoside hydrolase fused with the cyclin box domain. In this study, we characterized the catalytic activity, enzymatic properties, three-dimensional structure, and physiological role of the gene product, GtBxlA. The enzyme was produced as a thermostable dimer, acting on p-nitrophenyl-beta-d-xylopyranoside among 23 substrates. beta-1,4-Linked xylooligosaccharides were also hydrolyzed from the nonreducing end. The activity indicated that GtBxlA functions as an exo-beta-1,4-xylosidase. We determined the crystal structure of the Glu188Ala variant complexed with beta-1,4-xylotriose at 1.52 A resolution. GtBxlA exhibited an atypical (beta/alpha)(8)-barrel architecture. The cyclin box constituted a single alpha-helix within the core barrel and a lid-like domain that contributes to dimer formation. Structural analysis revealed that Glu188 and Glu318 are positioned to serve as the acid/base and nucleophile catalysts, respectively. Alanine mutagenesis confirmed the essential role of Glu188 and Glu318 in catalysis. We also determined the ligand-free structure of the Glu188Ala variant. Both structures were almost identical; however, a loop at the substrate entry site was fixed in the ligand-free structure, suggesting a conformational change upon substrate binding. Although bxlA deletion did not affect beta-1,4-xylan utilization, its expression was induced by beta-1,4-xylan. These observations suggest that G. thermodenitrificans OS27 employed GtBxlA in utilizing beta-1,4-xylan. Notably, GtBxlA could hydrolyze beta-1,3-linked xylooligosaccharides. This highlights the possibility that GtBxlA also assists the host in utilizing beta-1,3-xylan, which is abundant in certain seaweeds.

Structural and biochemical characterization of a GH5_22 enzyme from the seaweed-derived thermophile Geobacillus thermodenitrificans OS27.,Lee W, Hino T, Fujii K, Tanimoto S, Naka R, Hara K, Okamoto T, Okazaki F, Nagano S, Ohshiro T, Suzuki H Arch Biochem Biophys. 2026 Jan 16;778:110736. doi: 10.1016/j.abb.2026.110736. PMID:41548701<ref>PMID:41548701</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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== References ==
<references/>
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</StructureSection>
[[Category: Geobacillus thermodenitrificans]]
[[Category: Large Structures]]
[[Category: Hino T]]
[[Category: Lee W]]
[[Category: Nagano S]]
[[Category: Ohshiro T]]
[[Category: Okamoto T]]
[[Category: Suzuki H]]