PMID: 20356840

Authors:

Goncalves S, Borges N, Esteves AM, Victor BL, Soares CM, Santos H, Matias PM

Title:

Structural analysis of Thermus thermophilus HB27 mannosyl-3-phosphoglycerate synthase provides evidence for a second catalytic metal ion and new insight into the retaining mechanism of glycosyltransferases.

Journal:

J Biol Chem. 2010 Jun 4;285(23):17857-68. Epub 2010 Mar 31.

Abstract:

Mannosyl-3-phosphoglycerate synthase is a glycosyltransferase involved in the two-step synthetic pathway of mannosylglycerate, a compatible solute that accumulates in response to salt and/or heat stresses in many microorganisms thriving in hot environments. The three-dimensional structure of mannosyl-3-phosphoglycerate synthase from Thermus thermophilus HB27 in its binary complex form, with GDP-alpha-D-mannose and Mg(2+), shows a second metal binding site, about 6 A away from the mannose moiety. Kinetic and mutagenesis studies have shown that this metal site plays a role in catalysis. Additionally, Asp(167) in the DXD motif is found within van der Waals contact distance of the C1' atom in the mannopyranose ring, suggesting its action as a catalytic nucleophile, either in the formation of a glycosyl-enzyme intermediate according to the double-displacement S(N)2 reaction mechanism or in the stabilization of the oxocarbenium ion-like intermediate according to the D(N)*A(Nss) (S(N)i-like) reaction mechanism. We propose that either mechanism may occur in retaining glycosyltransferases with a GT-A fold, and, based on the gathered structural information, we identified an extended structural signature toward a common scaffold between the inverting and retaining glycosyltransferases.