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==Ketosteroid Isomerase KSI with 5-nitrobenzoxazole (5NBI)==
<StructureSection load='7epo' size='340' side='right'caption='[[7epo]], [[Resolution|resolution]] 2.35&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=7EPO OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=7EPO 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]] 2.35&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=H5J:5-nitro-1,2-benzoxazole'>H5J</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=7epo FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=7epo OCA], [https://pdbe.org/7epo PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=7epo RCSB], [https://www.ebi.ac.uk/pdbsum/7epo PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=7epo ProSAT]</span></td></tr>
</table>
<div style="background-color:#fffaf0;">
== Publication Abstract from PubMed ==
The Kemp elimination reaction, involving the ring-opening of benzoxazole and its derivatives under the action of natural enzymes or chemical catalysts, has been of interest to researchers since its discovery. Because this reaction does not exist in all currently known metabolic pathways, the computational design of Kemp eliminases has provided valuable insights into principles of enzymatic catalysis. However, it was discovered that the naturally occurring promiscuous enzymes ydbC, xapA and ketosteroid isomerase also can catalyze Kemp elimination. Here, we report the crystal structure of ketosteroid isomerase (KSI) from Mycobacterium smegmatis MC2 155. MsKSI crystallizes in the P212121 space group with two molecules in an asymmetric unit, and ultracentrifugation data confirms that it forms a stable dimer in solution, consistent with the 1.9 A-resolution structure. Our assays confirm that MsKSI accelerates the Kemp elimination of 5-nitrobenzoxazole (5NBI) with an optimal pH of 5.5. A 2.35 A resolution crystal structure of the MsKSI-5NBI complex reveals that the substrate 5NBI is bound in the active pocket of the enzyme composed of hydrophobic residues. In addition, the Glu127 residue is proposed to play an important role as a general base in proton transfer and breaking weak O-N bonds to open the five-membered ring. This work provides a starting point for exploring the artificial modification of MsKSI using the natural enzyme as the backbone.

Structural characterization and Kemp eliminase activity of the Mycobacterium smegmatis Ketosteroid Isomerase.,Liang Y, Li W, Liang H, Lou X, Liu R, Zhang Q, Bartlam M Biochem Biophys Res Commun. 2021 Jun 30;560:159-164. doi:, 10.1016/j.bbrc.2021.05.007. Epub 2021 May 13. PMID:33992958<ref>PMID:33992958</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
</div>
<div class="pdbe-citations 7epo" style="background-color:#fffaf0;"></div>

==See Also==
*[[Ketosteroid Isomerase|Ketosteroid Isomerase]]
== References ==
<references/>
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</StructureSection>
[[Category: Large Structures]]
[[Category: Bartlam M]]
[[Category: Liang Y]]
[[Category: Zhang Q]]