THE 2.0-ANGSTROM RESOLUTION STRUCTURE OF ESCHERICHIA-COLI HISTIDINE-CONTAINING PHOSPHOCARRIER PROTEIN HPR - A REDETERMINATION

The x-ray structure of Escherichia coli HPr has been redetermined at 2 .0-angstrom resolution. In contrast to the previous study (El-Kabbani, O. A. L., Waygood, E. B., and Delbaere, L. T. J. (1987) J. Biol. Chem . 262, 12926-12929), the overall structure is, in general, similar to other reported NMR and x-ray HPr structures, although there are some i mportant differences in detail. The overall folding topology of HPr is a classical open-faced beta-sandwich, consisting of four antiparallel beta-strands and three alpha-helices. The least square refinement pro duced an R index of 0.135 for all measured unique data between 8.0 and 2.0 angstrom resolution. The active center consists of His15 which is hydrogen bonded to a sulfate anion, and Arg17 which has a fully open conformation. This corresponds to the first observed ''semi-closed'' c onformation of the active center of HPr. The Streptococcus faecalis HP r structure (Jia, Z., Vandonselaar, M., Quail, J. W., and Delbaere, L. T. J. (1993) Nature 361, 94-97) has the ''open'' conformation in whic h the side chains of His15 and Arg17 are directed as far away from eac h other as possible. The Bacillus subtilis HPr (Herzberg, O., Reddy, P ., Sutrina, S., Saier, M. H., Jr., Reizer, J., and Kapadia, G. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 2499-2503) has the ''closed'' conf ormation in which the side chains of His15 and Arg17 are close togethe r with a sulfate anion located in the active center. The open conforma tion represents the unphosphorylated form of HPr whereas the closed co nformation likely resembles the phosphorylated form of HPr. The semi-c losed conformation observed in the E. coli HPr structure could represe nt a structural intermediate on the phosphorylation/dephosphorylation pathway of HPr.