The non-hydrolysing bacterial UDP-N-acetylglucosamine 2-epimerase (UDP-GlcNAc 2-epimerase) catalyses the conversion of UDP-GlcNAc into UDP-N-acetylmannosamine, an intermediate in the biosynthesis of several cell-surface polysaccharides. This enzyme is allosterically regulated by its substrate UDP-GlcNAc.
The crystal structure (PDB ID code 3OT5) of a putative UDP-N-acetylglucosamine 2-epimerase from Listeria monocytogenes has been solved and refined to 2.2 A resolution. The asymmetric unit contains four copies of the protein. The homologous B. anthracis (PDB ID code 3BEO) and L. monocytogenes UDP-GlcNAc 2-epimerases share 65 % sequence identity and have rmsd values from 2.0 to 4.0 A in the positions of their 361 C-alpha atoms, as revealed by the pairwise structural alignment. These big overall differences might be related to the conformational changes that take place in protein upon binding of the substrate UDP-GlcNAc and the reaction intermediate UDP in the 3BEO structure. Indeed, superposition of the B. anthracis apo-UDP-GlcNAc 2-epimerase structure (PDB ID code 1O6C) and the 3OT5 structure shows rmsd values from 1.2 to 2.9 A over the aforementioned range of the C-alpha atoms. Additionally, both apo-form structures exhibit a high overall mean B value of 49.0 A2, whereas it is 13.0 A2 in the ternary complex 3BEO structure.