Crystal structures of the archaeal UDP-GlcNAc 2-epimerase from Methanocaldococcus jannaschii reveal a conformational change induced by UDP-GlcNAc.

Uridine diphosphate N-acetylglucosamine (UDP-GlcNAc) 2-epimerase catalyzes the interconversion of UDP-GlcNAc to UDP-N-acetylmannosamine (UDP-ManNAc), which is used in the biosynthesis of cell surface polysaccharides in bacteria. Biochemical experiments have demonstrated that mutation of this enzyme causes changes in cell morphology and the thermoresistance of the cell wall. Here, we present the crystal structures of Methanocaldococcus jannaschii UDP-GlcNAc 2-epimerase in open and closed conformations. A comparison of these crystal structures shows that upon UDP and UDP-GlcNAc binding, the enzyme undergoes conformational changes involving a rigid-body movement of the C-terminal domain. We also present the crystal structure of Bacillus subtilis UDP-GlcNAc 2-epimerase in the closed conformation in the presence of UDP and UDP-GlcNAc. Although a structural overlay of these two closed-form structures reveals that the substrate-binding site is evolutionarily conserved, some areas of the allosteric site are distinct between the archaeal and bacterial UDP-GlcNAc 2-epimerases. This is the first report on the crystal structure of archaeal UDP-GlcNAc 2-epimerase, and our results clearly demonstrate the changes between the open and closed conformations of this enzyme.