Crystal structure of Streptococcus pneumoniae N-acetyl-glucosamine-1-phosphate uridyltransferase bound to acetyl-coenzyme A reveals a novel active site architecture

The bifunctional bacterial enzyme N-acetyl-glucosamine-1-phosphate uridyltr ansferase (GLmU) catalyzes the two-step formation of UDP-GlcNAc, a fundamen tal precursor in bacterial cell wall biosynthesis. With the emergence of ne w resistance mechanisms against beta -lactam and glycopeptide antibiotics, the biosynthetic pathway of UDP-GlcNAc represents an attractive target for drug design of new antibacterial agents. The crystal structures of Streptoc occus pneumoniae GlmU in unbound form, in complex with acetyl-coenzyme A (A cCoA) and in complex with both AcCoA and the end product UDP-GlcNAc, have b een determined and refined to 2.3, 2.5, and 1.75 Angstrom, respectively. Th e S. pneumoniae GlmU molecule is organized in two separate domains connecte d via a long cu-helical linker and associates as a trimer, with the 50-Angs trom -long left-handed beta -helix (LPH) C-terminal domains packed against each other in a parallel fashion and the C-terminal region extended far awa y from the LPH core and exchanged with the beta -helix from a neighboring s ubunit in the trimer, AcCoA binding induces the formation of a long and nar row tunnel, enclosed between two adjacent LPH domains and the interchanged C-terminal region of the third subunit, giving rise to an original active s ite architecture at the junction of three subunits.