6b2m
LarE, a sulfur transferase involved in synthesis of the cofactor for lactate racemase in complex with coenzyme A
Structural highlights
FunctionLARE_LACPL Involved in the biosynthesis of a nickel-pincer cofactor ((SCS)Ni(II) pincer complex). Catalyzes the ATP-dependent incorporation of two sulfur atoms in pyridinium-3,5-biscarboxylic acid mononucleotide (P2CMN) to yield pyridinium-3,5-bisthiocarboxylic acid mononucleotide (P2TMN). The source of sulfur is the enzyme itself: Cys-176 of LarE is the sulfur donor, thereby being converted into dehydroalanine, and is not regenerated in vivo. Thus, two molecules of LarE undergo sacrificial sulfur transfer to create one P2TMN (PubMed:27114550). Binds nickel (PubMed:24710389). Is required for the activation of the lactate racemase LarA (PubMed:24710389). May also be involved in the activation of other nickel-pincer cofactor-dependent enzymes (PubMed:27114550).[1] [2] Publication Abstract from PubMedLarE from Lactobacillus plantarum is an ATP-dependent sulfur transferase that sacrifices its Cys176 sulfur atom to form a dehydroalanine (Dha) side chain during biosynthesis of the covalently linked nickel-pincer nucleotide (NPN) cofactor (pyridinium 3-thioamide-5-thiocarboxylic acid mononucleotide) of lactate racemase. Coenzyme A (CoA) stabilizes LarE and forms a CoA-Cys176 mixed disulfide with the protein. This study presents the crystal structure of the LarE/CoA complex, revealing protein interactions with CoA that mimic those for binding ATP. CoA weakly inhibits LarE activity, and the persulfide of CoA is capable of partially regenerating functional LarE from the Dha176 form of the protein. The physiological relevance of this cycling reaction is unclear. A new form of LarE was discovered, an NPN-LarE covalent adduct, explaining prior results in which activation of the lactate racemase apoprotein required only the isolated LarE. The crystal structure of the inactive C176A variant revealed a fold essentially identical to that of wild-type LarE. Additional active site variants of LarE were created and their activities characterized, with all LarE variants analyzed in terms of the structure. Finally, the L. plantarum LarE structure was compared to a homology model of Thermoanaerobacterium thermosaccharolyticum LarE, predicted to contain three cysteine residues at the active site, and to other proteins with a similar fold and multiple active site cysteine residues. These findings suggest that some LarE orthologs may not be sacrificial but instead may catalyze sulfur transfer by using a persulfide mechanism or from a labile site on a [4Fe-4S] cluster at this position. Analysis of the Active Site Cysteine Residue of the Sacrificial Sulfur Insertase LarE from Lactobacillus plantarum.,Fellner M, Rankin JA, Desguin B, Hu J, Hausinger RP Biochemistry. 2018 Sep 11. doi: 10.1021/acs.biochem.8b00601. PMID:30157639[3] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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