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==Crystal Structure of N-acetylneuraminic acid lyase from Staphylococcus aureus with the chemical modification thia-lysine at position 165==
<StructureSection load='4aho' size='340' side='right'caption='[[4aho]], [[Resolution|resolution]] 2.00&Aring;' scene=''>
== Structural highlights ==
<table><tr><td colspan='2'>[[4aho]] is a 4 chain structure with sequence from [https://en.wikipedia.org/wiki/Staphylococcus_aureus_subsp._aureus_NCTC_8325 Staphylococcus aureus subsp. aureus NCTC 8325]. Full crystallographic information is available from [http://oca.weizmann.ac.il/oca-bin/ocashort?id=4AHO OCA]. For a <b>guided tour on the structure components</b> use [https://proteopedia.org/fgij/fg.htm?mol=4AHO 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&#8491;</td></tr>
<tr id='ligand'><td class="sblockLbl"><b>[[Ligand|Ligands:]]</b></td><td class="sblockDat" id="ligandDat"><scene name='pdbligand=CL:CHLORIDE+ION'>CL</scene>, <scene name='pdbligand=SLZ:L-THIALYSINE'>SLZ</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=4aho FirstGlance], [http://oca.weizmann.ac.il/oca-bin/ocaids?id=4aho OCA], [https://pdbe.org/4aho PDBe], [https://www.rcsb.org/pdb/explore.do?structureId=4aho RCSB], [https://www.ebi.ac.uk/pdbsum/4aho PDBsum], [https://prosat.h-its.org/prosat/prosatexe?pdbcode=4aho ProSAT]</span></td></tr>
</table>
== Function ==
[https://www.uniprot.org/uniprot/NANA_STAA8 NANA_STAA8] Catalyzes the cleavage of N-acetylneuraminic acid (sialic acid) to form pyruvate and N-acetylmannosamine via a Schiff base intermediate (By similarity).
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== Publication Abstract from PubMed ==
Chemical modification has been used to introduce the unnatural amino acid gamma-thialysine in place of the catalytically important Lys165 in the enzyme N-acetylneuraminic acid lyase (NAL). The Staphylococcus aureus nanA gene, encoding NAL, was cloned and expressed in E. coli. The protein, purified in high yield, has all the properties expected of a class I NAL. The S. aureus NAL which contains no natural cysteine residues was subjected to site-directed mutagenesis to introduce a cysteine in place of Lys165 in the enzyme active site. Subsequently chemical mutagenesis completely converted the cysteine into gamma-thialysine through dehydroalanine (Dha) as demonstrated by ESI-MS. Initial kinetic characterisation showed that the protein containing gamma-thialysine regained 17 % of the wild-type activity. To understand the reason for this lower activity, we solved X-ray crystal structures of the wild-type S. aureus NAL, both in the absence of, and in complex with, pyruvate. We also report the structures of the K165C variant, and the K165-gamma-thialysine enzyme in the presence, or absence, of pyruvate. These structures reveal that gamma-thialysine in NAL is an excellent structural mimic of lysine. Measurement of the pH-activity profile of the thialysine modified enzyme revealed that its pH optimum is shifted from 7.4 to 6.8. At its optimum pH, the thialysine-containing enzyme showed almost 30 % of the activity of the wild-type enzyme at its pH optimum. The lowered activity and altered pH profile of the unnatural amino acid-containing enzyme can be rationalised by imbalances of the ionisation states of residues within the active site when the pK(a) of the residue at position 165 is perturbed by replacement with gamma-thialysine. The results reveal the utility of chemical mutagenesis for the modification of enzyme active sites and the exquisite sensitivity of catalysis to the local structural and electrostatic environment in NAL.

Structural Insights into the Recovery of Aldolase Activity in N-Acetylneuraminic Acid Lyase by Replacement of the Catalytically Active Lysine with gamma-Thialysine by Using a Chemical Mutagenesis Strategy.,Timms N, Windle CL, Polyakova A, Ault JR, Trinh CH, Pearson AR, Nelson A, Berry A Chembiochem. 2013 Mar 4;14(4):474-81. doi: 10.1002/cbic.201200714. Epub 2013 Feb , 18. PMID:23418011<ref>PMID:23418011</ref>

From MEDLINE&reg;/PubMed&reg;, a database of the U.S. National Library of Medicine.<br>
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<div class="pdbe-citations 4aho" style="background-color:#fffaf0;"></div>

==See Also==
*[[N-acetylneuraminate lyase 3D structures|N-acetylneuraminate lyase 3D structures]]
== References ==
<references/>
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</StructureSection>
[[Category: Large Structures]]
[[Category: Staphylococcus aureus subsp. aureus NCTC 8325]]
[[Category: Berry A]]
[[Category: Nelson A]]
[[Category: Polyakova A]]
[[Category: Timms N]]
[[Category: Trinh AR]]
[[Category: Trinh CH]]
[[Category: Windle CL]]