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Publication Abstract from PubMed

Bacterial lactate racemase is a nickel-dependent enzyme that contains a cofactor, nickel pyridinium-3,5-bisthiocarboxylic acid mononucleotide, hereafter named nickel-pincer nucleotide (NPN). The LarC enzyme from the bacterium Lactobacillus plantarum participates in NPN biosynthesis by inserting nickel ion into pyridinium-3,5-bisthiocarboxylic acid mononucleotide,. This reaction, known in organometallic chemistry as a cyclometalation, is characterized by the formation of new metal-carbon and metal-sulfur sigma bonds. LarC is therefore the first cyclometallase identified in nature, but the molecular mechanism of LarC-catalyzed cylometalation is unknown. Here, we show that LarC activity requires Mn(2+)-dependent CTP hydrolysis. The crystal structure of the C-terminal domain of LarC at 1.85 A resolution revealed a hexameric ferredoxin-like fold and an unprecedented CTP binding pocket. The loss of function of LarC variants with alanine variants of acidic residues lead us to propose a carboxylate-assisted mechanism for nickel insertion. This works also demonstrates the in vitro synthesis and purification of the NPN cofactor, opening new opportunities for the study of this intriguing cofactor and of NPN-utilizing enzymes.

Biosynthesis of the nickel-pincer nucleotide cofactor of lactate racemase requires a CTP-dependent cyclometallase.,Desguin B, Fellner M, Riant O, Hu J, Hausinger R, Hols P, Soumillion P J Biol Chem. 2018 Jun 10. pii: RA118.003741. doi: 10.1074/jbc.RA118.003741. PMID:29887527^[3]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.