STRUCTURE AND FUNCTION OF THE DIHYDROPTEROATE SYNTHASE FROM STAPHYLOCOCCUS-AUREUS

The gene encoding the dihydropteroate synthase of staphylococcus aureu s has been cloned, sequenced and expressed in Escherichia coli. The pr otein has been purified for biochemical characterization and X-ray cry stallographic studies. The enzyme is a dimer in solution, has a steady state kinetic mechanism that suggests random binding of the two subst rates and half-site reactivity. The crystal structure of ape-enzyme an d a binary complex with the substrate analogue hydroxymethylpterin pyr ophosphate were determined at 2.2 Angstrom and 2.4 Angstrom resolution , respectively. The enzyme belongs to the group of ''TIM-barrel'' prot eins and crystallizes as a non-crystallographic dimer. Only one molecu le of the substrate analogue bound per dimer in the crystal. Sequencin g of nine sulfonamide-resistant clinical isolates has shown that as ma ny as 14 residues could be involved in resistance development. The res idues are distributed over the surface of the protein, which defies a simple interpretation of their roles in resistance. Nevertheless, the three-dimensional structure of the substrate analogue binary complex c ould give important insight into the molecular mechanism of this enzym e. (C) 1997 Academic Press Limited.