Tertiary structure of histidine-containing protein of the phosphoenolpyruvate:sugar phosphotransferase system of Escherichia coli.

The tertiary structure of the histidine-containing phosphocarrier protein (HPr) of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system has been determined by x-ray diffraction at 2.8-A resolution. Initially, a partial structure was fitted to the multiple isomorphous replacement map and then least-squares refined by the Konnert/Hendrickson restrained parameter method (Konnert, J. H., and Hendrickson, W. A. (1980) Acta Crystallogr. A36, 344-350) and finally, a subsequent map was computed by use of the phase combination method of Read (Read, R. J. (1986) Acta Crystallogr. A42, 140-149). More of the protein structure was located in the latter map. The procedure of model building, least-squares refinement, and electron density map recalculation was repeated until the tertiary structure of HPr was obtained. The overall structure of HPr consists of four beta-strands, three helical regions, and four beta-turns. At the active center, the His15 imidazole interacts with one oxygen atom of the alpha-carboxyl C terminus of the polypeptide chain; the conserved Arg17 side chain interacts with the other oxygen atom of the alpha-carboxyl C terminus as well as with the side chain of Glu85. This is the first x-ray analysis of a protein of the phosphoenolpyruvate:sugar phosphotransferase system. Furthermore, this work represents a protein structure which has been solved by starting with a model that represented only one-third of the scattering matter.