Solution structure of the histidine-containing phosphocarrier protein fromStaphylococcus carnosus

The solution structure of histidine-containing phosphocarrier protein fromStaphylococcus carnosus was determined by two- and three-dimensional nuclear magnetic resonance (NMR) spectroscopy on uniformly¹⁵N-enriched protein. The main structural element is an antiparallel β-pleated sheet with four strands A, B, C, and D arranged with the topology A-D-B-C. Strand A comprises residues 2 to 8, strand B residues 32 to 37, strand C reidues 40 to 43, and strand D residues 59 to 66. Three right-handed helices are arranged on top of the β-pleated sheet. Helix a reaches from residue 16 to 29, helix b from residue 48 to 53, and helix c from residue 72 to 83. Strands B and C of the β-pleated sheet are connected by a type II turn. The hydroxyl proton of Ser-31 is exchanging with the solvent so slowly that cross peaks can be detected in two-dimensional NMR spectra based on homonuclearJ-couplings. The imidazole ring of the active-center His-15, which is partly charged in the structure determined at pH 7.2, is located above the N-terminal end of helix a, perpendicular to its axis. The N^δ1 atom of His-15, accepting the phosphoryl from enzyme I, is exposed to the solvent.