Lactate racemase

<h2 id="structure-and-properties">Structure and properties</h2>
The <a href="/facts/Molecular_weight/FWueGMed">molecular weight</a> of lactate racemase differs in the various organisms in which it has been found, ranging from 25,000 to 82,400 g/mol.<a class="footnote-ref" id="fnref:5" href="#fn:5">5</a> The structure of the enzyme from L. plantarum was solved by Jian Hu and Robert P. Hausinger of <a href="/facts/Michigan_State_University/faLD1NUz">Michigan State University</a> and co-workers there and elsewhere.<a class="footnote-ref" id="fnref:6" href="#fn:6">6</a> The protein contains a previously unknown covalently-linked nickel-pincer nucleotide (NPN) cofactor (pyridinium 3-thioamide-5-thiocarboxylic acid mononucleotide), where the nickel atom is bound to C4 of the pyridinium ring and two sulfur atoms. This cofactor participates in a proton-coupled hydride-transfer mechanism.<a class="footnote-ref" id="fnref:7" href="#fn:7">7</a>
There have been a number of recent studies on NPN cofactor synthesis by the LarB, LarE, and LarC proteins. LarB is a carboxylase/hydrolase of <a href="/facts/Nicotinamide_adenine_dinucleotide/BHdLW925">nicotinamide adenine dinucleotide</a> (NAD), providing pyridinium-3,5-dicarboxylic acid mononucleotide and <a href="/facts/Adenosine_monophosphate/D9Ryfqad">adenosine monophosphate</a> (AMP).<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a> LarE is an ATP-dependent sulfur transferase that converts the two substrate carboxyl groups into thioacids by sacrificing the sulfur atoms of a <a href="/facts/Cysteine/kbqvUm6d">cysteine</a> residue in the protein.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> Finally, LarC inserts nickel into the organic <a href="/facts/Ligand/6etB3qeW">ligand</a> by a CTP-dependent process to complete synthesis of the NPN cofactor.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>

<h2 id="enzyme-activity">Enzyme activity</h2>
In many of the species containing lactate racemase, the physiological role of the enzyme is to convert substrate D-lactate into L-lactate. In other species, such as L. plantarum, the cellular role is to transform L-lactate into D-lactate for incorporation into the cell wall.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a>
The in vitro reaction catalyzed by the enzyme reaches equilibrium at the point where approximately equimolar concentrations of the D- and L-isomers exist.<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>
L. plantarum initially produces L-lactate, which induces the activity of lactate racemase. By contrast, D-lactate represses lactate racemase activity in this species. Therefore, Lar activity appears to be regulated by the ratio of L-lactate/D-lactate. L. plantarum LarA represents a new type of nickel-dependent enzyme, due to its novel nickel-<a href="/facts/Pincer_ligand/4XFDy5kH">pincer ligand</a> ligand cofactor.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a>

<h2 id="importance">Importance</h2>
Two pathways appear to exist in L. plantarum for transforming <a href="/facts/Pyruvate/qJTgl4J9">pyruvate</a> into D-<a href="/facts/Lactic_acid/BsVRFx7s">lactate</a>. One of them involves the NAD-dependent lactate dehydrogenase that directly produces D-lactate (LdhD), and the other is through the sequential activities of an L-specific lactate dehydrogenase followed by lactate racemase. If the LdhD enzyme is inactivated or inhibited, lactate racemase provides the bacterium with a rescue pathway for the production of D-lactate.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> This pathway is significant because the production of D-lactate in L. plantarum is linked to the biosynthesis of the cell wall. Mutants lacking LdhD activity that also had the lar operon deleted only produced L-lactate, and peptidoglycan biosynthesis was not able to occur.

<h2 id="references">References</h2>

<ol>
<li id="fn:1">"DBGET Result: ENZYME 5.1.2.1". Retrieved 2007-06-03. <a href="http://www.genome.ad.jp/dbget-bin/www_bget?ec:5.1.2.1" target="_blank">http://www.genome.ad.jp/dbget-bin/www_bget?ec:5.1.2.1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">Goffin P; Deghorain M; Mainardi J-L; et al. (2005). "Lactate racemization as a rescue pathway for supplying D-lactate to the cell wall biosynthesis machinery in Lactobacillus plantarum". J. Bacteriol. 187 (19): 6750–61. doi:10.1128/JB.187.19.6750-6761.2005. PMC 1251571. PMID 16166538. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1251571" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1251571</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">Desguin B, Goffin P, Viaene E, Kleerebezem M, Martin-Diaconescu V, Maroney MJ, Declercq JP, Soumillion P, Hols P (2014). "Lactate racemase is a nickel-dependent enzyme activated by a widespread maturation system". Nat. Commun. 5: 3615. doi:10.1038/ncomms4615. PMC 4066177. PMID 24710389. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4066177" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4066177</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">Hiyama T, Fukui S, Kitahara K (1968). "Purification and Properties of Lactate Racemase from Lactobacillus sake". J. Biochem. 64 (1): 99–107. doi:10.1093/oxfordjournals.jbchem.a128870. PMID 5707819. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"BRENDA: Entry of Lactate racemase(EC-Number 5.1.2.1 )". Archived from the original on 2016-03-03. Retrieved 2007-06-03. <a href="https://web.archive.org/web/20160303171558/http://www.brenda.uni-koeln.de/php/result_flat.php4?ecno=5.1.2.1" target="_blank">https://web.archive.org/web/20160303171558/http://www.brenda.uni-koeln.de/php/result_flat.php4?ecno=5.1.2.1</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Desguin B, Zhang T, Soumillion P, Hols P, Hu J, Hausinger RP (2015). "A tethered niacin-derived pincer complex with a nickel-carbon bond in lactate racemase". Science. 349 (6243): 66–69. doi:10.1126/science.aab2272. PMID 26138974. S2CID 206637903. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">Rankin JA, Mauban RC, Fellner M, Desguin B, McCracken J, Hu J, Varganov SA, Hausinger RP (2018). "Lactate Racemase Nickel-Pincer Cofactor Operates by a Proton-Coupled Hydride Transfer Mechanism". Biochemistry. 57 (23): 3244–3251. doi:10.1021/acs.biochem.8b00100. OSTI 1502215. PMID 29489337. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">Desguin B, Soumillion P, Hols P, Hausinger RP (2016). "Nickel-pincer cofactor biosynthesis involves LarB-catalyzed pyridinium carboxylation and LarE-dependent sacrificial sulfur insertion". Proc. Natl. Acad. Sci. USA. 113 (20): 5598–5603. doi:10.1073/pnas.1600486113. PMC 4878509. PMID 27114550. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4878509" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4878509</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Fellner M, Rankin JA, Desguin B, Hu J, Hausinger RP (2018). "Analysis of the Active Site Cysteine Residue of the Sacrificial Sulfur Insertase LarE from Lactobacillus plantarum". Biochemistry. 57 (38): 5513–5523. doi:10.1021/acs.biochem.8b00601. OSTI 1476089. PMID 30157639. S2CID 52117187. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Desguin B, Fellner M, Riant O, Hu J, Hausinger RP, Hols P, Soumillion P (2018). "Biosynthesis of the nickel-pincer nucleotide cofactor of lactate racemase requires a CTP-dependent cyclometallase". J. Biol. Chem. 293 (32): 12303–12317. doi:10.1074/jbc.RA118.003741. PMC 6093250. PMID 29887527. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6093250" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6093250</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Goffin P; Deghorain M; Mainardi J-L; et al. (2005). "Lactate racemization as a rescue pathway for supplying D-lactate to the cell wall biosynthesis machinery in Lactobacillus plantarum". J. Bacteriol. 187 (19): 6750–61. doi:10.1128/JB.187.19.6750-6761.2005. PMC 1251571. PMID 16166538. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1251571" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1251571</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">Hiyama T, Fukui S, Kitahara K (1968). "Purification and Properties of Lactate Racemase from Lactobacillus sake". J. Biochem. 64 (1): 99–107. doi:10.1093/oxfordjournals.jbchem.a128870. PMID 5707819. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Desguin B, Zhang T, Soumillion P, Hols P, Hu J, Hausinger RP (2015). "A tethered niacin-derived pincer complex with a nickel-carbon bond in lactate racemase". Science. 349 (6243): 66–69. doi:10.1126/science.aab2272. PMID 26138974. S2CID 206637903. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Goffin P; Deghorain M; Mainardi J-L; et al. (2005). "Lactate racemization as a rescue pathway for supplying D-lactate to the cell wall biosynthesis machinery in Lactobacillus plantarum". J. Bacteriol. 187 (19): 6750–61. doi:10.1128/JB.187.19.6750-6761.2005. PMC 1251571. PMID 16166538. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1251571" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1251571</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
</ol>

Lactate racemase open-in-new

Lactate racemase