THE 3-DIMENSIONAL STRUCTURE OF CAPSULE-SPECIFIC CMP - 2-KETO-3-DEOXY-MANNO-OCTONIC ACID SYNTHETASE FROM ESCHERICHIA-COLI

CMP-Kdo synthetases from Gram-negative bacteria activate Kdo for incor poration into lipo- and capsule-polysaccharides. Here we report the cr ystal structure of the capsule-specific synthetase from E. coli at 2.3 Angstrom resolution. The enzyme is a dimer of 2 X 245 amino acid resi dues assuming C-2 symmetry. It contains a central predominantly parall el beta-sheet with surrounding helices. The chain fold is novel; it is remotely related to a double Rossmann fold. A large pocket at the car boxyl terminal ends of the central beta-strands most likely accommodat es the catalytic center. A putative phosphate binding site at the loop between the first beta-strand and the following helix is indicated by a bound iridium hexachloride anion.