Sugar transport by the bacterial phosphotransferase system. Primary structure and active site of a general phosphocarrier protein (HPr) from Salmonella typhimurium.

The general histidine-containing phosphocarrier protein (HPr) of the Salmonella phosphotransferase system is required for the phosphorylation of all sugar substrates by this system. The complete amino acid sequence of HPr, consisting of 84 amino acid residues, has been established. The sequence was determined by cleaving the protein with cyanogen bromide, trypsin, and with a protease from Staphylococcus aureus, followed by isolation and amino acid sequence determination of the resulting peptides. The Salmonella typhimurium protein contains two histidine residues, at positions 15 and 75, respectively. The phosphoryl group in phospho-HPr was linked to the His-15 residue. Based on several lines of evidence, the HPr protein from Escherichia coli appears to be identical with the protein from S. typhimurium. The HPr protein from S. aureus has also been isolated in this laboratory and was shown to differ from the HPr proteins described above both with respect to amino acid composition and the inability of the S. aureus and E. coli HPR proteins to substitute for each other in the in vitro sugar phosphorylation assays. The complete amino acid sequence of S. aureus HPr has been reported (Beyreuther, K., Raufuss, H., Schrecker, O., and Hengstenberg, W. (1977) Eur. J. Biochem. 75, 275-286), and its secondary structure has been predicted; this protein contains 70 amino acid residues and only one histidine. In the present studies, three methods were used to predict the secondary structure of S. typhimurium HPr, the results were combined, and a secondary structure for the protein is proposed. Although the amino acid compositions and sequences of the S. typhimurium and S. aureus HPr proteins are quite different, 13 residues are identical in the sequence of the two proteins, and most of these are located near the active site histidine residue. In addition, the predicted secondary structures of the two proteins are quite similar; the additional 14 residues in S. typhimurium, located at the carboxyl terminal end, are predicted to form an alpha-helix.