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Publication Abstract from PubMed

Remarkable progress has been made in recent years in understanding the structural basis of glycosyl transfer. Nevertheless, the nature and relevance of the conformational changes associated with substrate recognition and catalysis remain poorly understood. Here we have focused on the glucosyl-3-phosphoglycerate synthase (GpgS), a retaining enzyme that initiates the biosynthetic pathway of methylglucose lipopolysaccharides (MGLPs) in mycobacteria. Evidence is provided that GpgS displays an unusually broad metal-ion specificity for a GT-A enzyme, with Mg2+, Mn2+, Ca2+, Co2+ and Fe2+ assisting catalysis. Interestingly, in the crystal structure of the apo form of GpgS, we have observed that a flexible loop adopts a double-conformation LA and LI in the active site of both monomers of the protein dimer. Notably, the LA loop geometry corresponds to an active conformation and is conserved in two other relevant states of the enzyme, namely the GpgS/metal/nucleotide-sugar donor and the GpgS/metal/nucleotide/acceptor bound complexes, indicating that GpgS is intrinsically in a catalytically active conformation. The crystal structure of GpgS in the presence of Mn2+/UDP/phosphoglyceric acid revealed an alternate conformation for the nucleotide-sugar beta-phosphate, which likely occurs upon sugar transfer. Moreover, structural, biochemical and biophysical data point to a crucial role of the beta-phosphate in donor and acceptor substrates binding and catalysis. Altogether our experimental data suggest a model wherein the catalytic site is essentially preformed, with a few conformational changes of lateral chain residues as the protein proceeds along the catalytic cycle. This model of action may be applicable to a broad range of GT-A glycosyltransferases.

Mechanistic insights into the retaining glucosyl-3-phosphoglycerate synthase from mycobacteria.,Urresti S, Albesa-Jove D, Schaeffer F, Pham HT, Kaur D, Gest P, van der Woerd MJ, Carreras-Gonzalez A, Lopez-Fernandez S, Alzari PM, Brennan PJ, Jackson M, Guerin ME J Biol Chem. 2012 May 25. PMID:22637481^[2]

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