Crystal structure of CTP:glycerol-3-phosphate cytidylyltransferase from Staphylococcus aureus: Examination of structural basis for kinetic mechanism

Integrity of the cell wall is essential for bacterial survival, and as a consequence components involved in its biosynthesis can potentially be exploited as targets for antibiotics. One such potential target is CTP:glycerol-3-phosphate cytidylyltransferase. This enzyme (TarDSa in Staphylococcus aureus and TagDBs in Bacillus subtilis) catalyzes the formation of CDP-glycerol, which is used for the assembly of linkages between peptidoglycan and teichoic acid polymer in Gram-positive bacteria. Intriguingly, despite the high sequence identity between TarDSa and TagDBs (69% identity), kinetic studies show that these two enzymes differ markedly in their kinetic mechanism and activity. To examine the basis for the disparate enzymological properties, we have determined the crystal structure of TarDSa in the apo state to 3 Å resolution, and performed equilibrium sedimentation analysis. Comparison of the structure with that of CTP- and CDP-glycerol-bound TagDBs crystal structures reveals that the overall structure of TarDSa is essentially the same as that of TagDBs, except in the C-terminus, where it forms a helix in TagDBs but is disordered in the apo TarDSa structure. In addition, TarDSa can exist both as a tetramer and as a dimer, unlike TagDBs, which is a dimer. These observations shed light on the structural basis for the differing kinetic characteristics between TarDSa and TagDBs.