We describe a small family of proteins, CHR, which contains members that function in chromate and/or sulfate transport. CHR proteins occur in bacteria and archaea. They consist of about 400 amino acyl residues, appear to have 10 transmembrane α-helical segments in an unusual 4+6 arrangement, and arose by an intragenic duplication event.

The permeases of the Escherichia coli phosphoenolpyruvate:sugar phosphotransferase system (PTS), the sugar-specific enzymes II, are energized by sequential phosphoryl transfer from phosphoenolpyruvate to (i) enzyme I, (ii) the phosphocarrier protein HPr, (iii) the enzyme IIA domains of the permeases, and (iv) the enzyme IIBC domains of the permeases which transport and phosphorylate their sugar substrates. A number of site-specific mutants of HPr were examined by using kinetic approaches. Most of the mutations exerted minimal effects on the kinetic parameters characterizing reactions involving phosphoryl transfer from phospho-HPr to various sugars. However, when the well-conserved aspartyl 69 residue in HPr was changed to a glutamyl residue, the affinities for phospho-HPr of the enzymes II specific for mannitol, N-acetylglucosamine, and ␤-glucosides decreased markedly without changing the maximal reaction rates. The same mutation reduced the spontaneous rate of phosphohistidyl HPr hydrolysis but did not appear to alter the rate of phosphoryl transfer from phospho-enzyme I to HPr. The bacterial phosphoenolpyruvate:sugar phosphotransferase system (PTS) catalyzes the concomitant chemoreception, transport, and phosphorylation of its numerous sugar substrates (19,27,32). It also regulates a variety of physiological processes in both gram-negative and gram-positive bacteria (31, 34). These processes include (i) catabolite repression, (ii) carbohydrate transport, (iii) carbon and energy metabolism, (iv) carbon storage, and (v) the coordination of carbon and nitrogen metabolism (20, 36). The regulatory functions of the PTS depend on its ability to serve as a protein kinase system. It phosphorylates various PTS and non-PTS proteins, thereby controlling their interactions with other macromolecules that influence catalysis or transcription. As some of these interactions apparently involve recognition of tertiary structure rather than primary structure (30), they can be influenced by alterations in residues distant from the sites of interaction (11,12,25,26,48,49).The generalized scheme for the PTS phosphoryl transfer chain is as follows (35): sugar sugar IIC sugar PEP™3 I ϳ P™3 HPr ϳ P™3 IIA ϳ P™3 IIB ϳ P™™™™3 sugar-P Several of these PTS proteins can transfer their phosphoryl moieties to non-PTS proteins (34). Central in this scheme is the small, non-sugar-specific phosphoryl transfer protein, HPr. It interacts with enzyme I, a variety of sugar-specific IIA protein constituents of the enzyme II complexes, and with non-PTS phosphorylation targets, including transcriptional antiterminators, non-PTS transport proteins, and enzymes (28,29,31,34).HPr of Escherichia coli is an 85-residue, heat-stable, singledomain, phosphoryl carrier protein (19,27). The amino acyl sequences of this protein and its homologs in various bacteria have been determined. Its homologs include fructose-inducible HPr-like protein domains, termed FPr (7, 50), the nitrogenrelated, regulatory HPr-like protein, termed NPr, encoded within the rpoN operon of ...