The crystal structure of E-coli pantothenate synthetase confirms it as a member of the cytidylyltransferase superfamily

Background: Pantothenate synthetase (EC 6.3.2.1) is the last enzyme of the pathway of pantothenate (vitamin B-5) synthesis. It catalyzes the condensat ion of pantoate with beta -alanine in an ATP-dependent reaction. Results: We describe the overexpression, purification, and crystal structur e of recombinant pantothenate synthetase from E. coli. The structure was so lved by a selenomethionine multiwavelength anomalous dispersion experiment and refined against native data to a final R-cryst of 22.6% (R-free = 24.9% ) at 1.7 Angstrom resolution. The enzyme is dimeric, with two well-defined domains per protomer: the N-terminal domain, a Rossmann fold, contains the active site cavity, with the C-terminal domain forming a hinged lid. Conclusions: The N-terminal domain is structurally very similar to class I aminoacyl-tRNA synthetases and is thus a member of the cytidylyltransferase superfamily. This relationship has been used to suggest the location of th e ATP and pantoate binding sites and the nature of hinge bending that leads to the ternary enzyme-pantoate-ATP complex.