Mechanics of solute translocation catalyzed by enzyme IImtl of the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli.

The kinetics of binding of mannitol to enzyme IImtl embedded in the membrane of vesicles with an inside-out or a right-side-out orientation were analyzed at 4 degrees C in the absence of the phosphoryl group donor, P-HPr. The binding to the right-side-out oriented vesicles equilibrated too fast to be monitored by the flow dialysis technique. On the other hand, with the inside-out oriented membrane vesicles two conformational changes of the enzyme could be detected kinetically. One change involved a recruitment of binding sites from a state of the enzyme where the binding sites were inaccessible from the cytoplasmic volume. The second change involved a conformational change of the enzyme that followed upon the initial binding to the cytoplasmic-facing binding site leading to a state with a higher affinity for mannitol. Equilibrium binding to the inside-out and right-side-out oriented membrane vesicles at 4 degrees C indicated that the two transitions did not represent the translocation of the binding site, free and with mannitol bound to it, to the other side of the membrane. Instead, a model is proposed in which the conformational changes represent transitions from states with the binding pocket opened to the cytoplasmic side of the membrane to occluded states of the enzyme in which the binding sites, with or without mannitol bound, are not accessible to either side of the membrane.     

Interaction between the cytoplasmic and membrane-bound domains of enzyme IImtl of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system

Sulfhydryl reagents affected the binding properties of the translocator domain, NIII, of enzyme IImtl in two ways: (i) the affinity for mannitol was reduced, and (ii) the exchange rate of bound and free mannitol was increased. The effect on the affinity was very much reduced after solubilization of enzyme IImtl in the detergent decylPEG. The effects were caused exclusively by reaction of the sulfhydryl reagents with the cysteine residue at position 384 in the primary sequence. Interaction between two domains is involved, since Cys384 is located in the cytoplasmic domain, CII. When Cys384 was mutated to serine, the enzyme exhibited the same binding properties as the chemically modified enzyme. The data support our proposal that phosphorylation of enzyme IImtl drastically reduces the activation energy for the translocation step through interaction between domains CII and NIII [Lolkema J. S., ten Hoeve-Duurkens, R. H., Swaving Dijkstra, D., & Robillard, G. T. (1991) Biochemistry (preceding paper in this issue)]. Functional interaction between the translocator domain, NIII, and domain CI was investigated by phosphorylation of His554, located in domain CI, in the C384S mutant. No effect on the binding properties was observed. In addition, the binding properties were insensitive to the presence of the soluble phosphotransferase components enzyme I and HPr.     

Analysis of mutations that uncouple transport from phosphorylation in enzyme IIGlc of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system.

Mutations that uncouple glucose transport from phosphorylation were isolated in plasmid-encoded Escherichia coli enzyme IIGlc of the phosphoenolpyruvate-dependent phosphotransferase system (PTS). The uncoupled enzymes IIGlc were able to transport glucose in the absence of the general phosphoryl-carrying proteins of the PTS, enzyme I and HPr, although with relatively low affinity. Km values of the uncoupled enzymes IIGlc for glucose ranged from 0.5 to 2.5 mM, 2 orders of magnitude higher than the value of normal IIGlc. Most of the mutant proteins were still able to phosphorylate glucose and methyl alpha-glucoside (a non-metabolizable glucose analog specific for IIGlc), indicating that transport and phosphorylation are separable functions of the enzyme. Some of the uncoupled enzymes IIGlc transported glucose with a higher rate and lower apparent Km in a pts+ strain than in a delta ptsHI strain lacking the general proteins enzyme I and HPr. Since the properties of these uncoupled enzymes IIGlc in the presence of PTS-mediated phosphoryl transfer resembled those of wild-type IIGlc, these mutants appeared to be conditionally uncoupled. Sequencing of the mutated ptsG genes revealed that all amino acid substitutions occurred in a hydrophilic segment within the hydrophobic N-terminal part of IIGlc. These results suggest that this hydrophilic loop is involved in binding and translocation of the sugar substrate.     

Dimeric enzyme IImtl of the E. coli phosphoenolpyruvate-dependent phosphotransferase system. Cross-linking studies with bifunctional sulfhydryl reagents

The occurrence of intermolecular dithiols on EIImtl has been studied with a number of thiol-specific cross-linking reagents. The reaction of EIImtl with bifunctional maleimide derivatives inactivates the enzyme. At the same time the enzyme is irreversibly cross-linked to a dimeric species. Under optimal conditions 50% of the protein is cross-linked upon reaction with the dimaleimides. The enzyme is also cross-linked under oxidizing conditions in the presence of CuCl2, presumably by oxidizing an intermolecular dithiol to a disulfide. This oxidation can be reversed by the addition of the reducing agent dithiothreitol. The reaction of phosphorylated EIImtl with the same sulfhydryl-specific bifunctional reagents does not lead to any cross-linked product. The results are discussed in terms of the association state of the purified protein and the distribution of its thiol groups.     

Staphylococcal phosphoenolpyruvate-dependent phosphotransferase system: purification and characterization of the mannitol-specific enzyme IIImtl of Staphylococcus aureus and Staphylococcus carnosus and homology with the enzyme IImtl of Escherichia coli

Enzyme IIImtl is part of the mannitol phosphotransferase system of Staphylococcus aureus and Staphylococcus carnosus and is phosphorylated by phosphoenolpyruvate in a reaction sequence requiring enzyme I (phosphoenolpyruvate-protein phosphotransferase) and the histidine-containing protein HPr. In this paper, we report the isolation of IIImtl from both S. aureus and S. carnosus and the characterization of the active center. After phosphorylation of IIImtl with [32P]PEP, enzyme I, and HPr, the phosphorylated protein was cleaved with endoproteinase Glu(C). The amino acid sequence of the S. aureus peptide carrying the phosphoryl group was found to be Gln-Val-Val-Ser-Thr-Phe-Met-Gly-Asn-Gly-Leu-Ala-Ile-Pro-His-Gly-Thr-Asp- Asp. The corresponding peptide from S. carnosus shows an equal sequence except that the first residue is Ala instead of Gln. These peptides both contain a single histidyl residue which we assume to carry the phosphoryl group. All proteins of the PTS so far investigated indeed carry the phosphoryl group attached to a histidyl residue. According to sodium dodecyl sulfate gels, the molecular weight of the IIImtl proteins was found to be 15,000. We have also determined the N-terminal sequence of both proteins. Comparison of the IIImtl peptide sequences and the C-terminal part of the enzyme IImtl of Escherichia coli reveals considerable sequence homology, which supports the suggestion that IImtl of E. coli is a fusion protein of a soluble III protein with a membrane-bound enzyme II. In particular, the homology of the active-center peptide of IIImtl of S. aureus and S. carnosus with the enzyme IImtl of E. coli allows one to predict the N-3 histidine phosphorylation site within the E. coli enzyme.     

Control of glucose metabolism by enzyme IIGlc of the phosphoenolpyruvate-dependent phosphotransferase system in Escherichia coli.

The quantitative effects of variations in the amount of enzyme IIGlc of the phosphoenolpyruvate:glucose phosphotransferase system (PTS) on glucose metabolism in Escherichia coli were studied. The level of enzyme IIGlc could be adjusted in vivo to between 20 and 600% of the wild-type chromosomal level by using the expression vector pTSG11. On this plasmid, expression of the structural gene for enzyme IIGlc, ptsG, is controlled by the tac promoter. As expected, the control coefficient (i.e., the relative increase in pathway flux, divided by the relative increase in amount of enzyme) of enzyme IIGlc decreased in magnitude if a more extensive pathway was considered. Thus, at the wild-type level of enzyme IIGlc activity, the control coefficient of this enzyme on the growth rate on glucose and on the rate of glucose oxidation was low, while the control coefficient on uptake and phosphorylation of methyl alpha-glucopyranoside (an enzyme IIGlc-specific, nonmetabolizable glucose analog) was relatively high (0.55 to 0.65). The implications of our findings for PTS-mediated regulation, i.e., inhibition of growth on non-PTS compounds by glucose, are discussed.     

Subunit structure and activity of the mannitol-specific enzyme II of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system solubilized in detergent

The original proposal of Saier stating that P-enolpyruvate-dependent mannitol phosphorylation is catalyzed by the monomeric form of the bacterial phosphotransferase enzyme IImtl, which would be the form predominantly existing in the phospholipid bilayer, whereas mannitol/mannitol-P exchange would depend on the transient formation of functional dimers, is refuted [Saier, M.H. (1980) J. Supramol. Struct. 14, 281-294]. The correct interpretation of the proportional relation between the rate of mannitol phosphorylation in the overall reaction and the enzyme concentration is that enzyme IImtl is dimeric under the conditions employed. Differences measured in the enzyme concentration dependency of the overall and exchange reactions were caused by different assay conditions. The dimer is favored over the monomer at high ionic strength and basic pH. Mg2+ ions bind specifically to enzyme IImtl, inducing dimerization. A complex formed by mixing inorganic phosphate, F-, and Mg2+ at sufficiently high concentrations inhibits enzyme IImtl, in part, by dissociation of the dimer. Enzyme IImtl was dimeric in 25 mM Tris, pH 7.6, and 5 mM Mg2+ over a large enzyme concentration range and under many different turnover conditions. The association/dissociation equilibrium was demonstrated in phosphate bufers, pH 6.3. The dimer was the most active form both in the overall and in the exchange reaction under the conditions assayed. The monomer was virtually inactive in mannitol/mannitol-P exchange but retained 25% of the activity in the overall reaction.     

Kinetics and subunit interaction of the mannitol-specific enzyme II of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system

Purified mannitol-specific enzyme II (EIImtl), in the presence of the detergent Lubrol, catalyzes the phosphorylation of mannitol from P-HPr via a classical ping-pong mechanism involving the participation of a phosphorylated EIImtl intermediate. This intermediate has been demonstrated by using radioactive phosphoenolpyruvate. Upon addition of mannitol, at least 80% of the enzyme-bound phosphoryl groups can be converted to mannitol 1-phosphate. The EIImtl concentration dependence of the exchange reaction indicates that self-association is a prerequisite for catalytic activity. The self-association can be achieved by increasing the EIImtl concentration or at low concentrations of EIImtl by adding HPr or bovine serum albumin. The equilibrium is shifted toward the dissociated form by mannitol 1-phosphate, resulting in a mannitol 1-phosphate induced inhibition. Mannitol does not affect the association state of the enzyme. Both mannitol and mannitol 1-phosphate also act as classical substrate inhibitors. The apparent Ki of each compound, however, is approximately equal to its apparent Km, suggesting that mannitol and mannitol 1-phosphate bind at the same site on EIImtl. Due to strong inhibition provided by mannitol and mannitol 1-phosphate in the exchange reaction, the kinetics of this reaction cannot be used to determine whether the reaction proceeds via a ping-pong or an ordered reaction mechanism.     

Details of mannitol transport in Escherichia coli elucidated by site-specific mutagenesis and complementation of phosphorylation site mutants of the phosphoenolpyruvate-dependent mannitol-specific phosphotransferase system

The mannitol transport protein (EIImtl) carries out translocation with concomitant phosphorylation of mannitol from the periplasm to the cytoplasm, at the expense of phosphoenolpyruvate (PEP). The phosphoryl group which is needed for this group translocation is sequentially transferred from PEP via two phosphorylation sites, located exclusively on the C-terminal cytoplasmic domain, to mannitol. Oligonucleotide-directed mutagenesis was used to investigate the precise role of these sites in phosphoryl group transfer, by producing specific amino acid substitutions. The first phosphorylation site, His-554 (P1), was replaced by Ala, which renders the EII-H554A completely inactive in PEP-dependent mannitol phosphorylation, but not in mannitol/mannitol 1-phosphate exchange. The P2 site mutant, EII-C384S, was inactive both in the mannitol phosphorylation reaction and in the exchange reaction, due to replacement of the essential Cys-384 by Ser. Although EII-H554A and EII-C384S were both catalytically inactive in the PEP-dependent phosphorylation, EII-C384S was able to restore up to 55% of the wild-type mannitol phosphorylation activity with the EII-H554A mutant, indicating a direct phosphotransfer between two subunits. These phosphorylation data together with the data obtained from mannitol/mannitol phosphate exchange kinetics, after mixing EII-H554A and EII-C384S, indicated the formation of functionally stable heterodimers, which consist of an EII-H554A and an EII-C384S monomer.     

Functional reconstitution of the purified phosphoenolpyruvate-dependent mannitol-specific transport system of Escherichia coli in phospholipid vesicles: coupling between transport and phosphorylation.

Purified mannitol-specific enzyme II (EII) from Escherichia coli was reconstituted into phospholipid vesicles with the aid of a detergent-dialysis procedure followed by a freeze-thaw sonication step. The orientation of EII in the proteoliposomes was random. The cytoplasmic moiety of the inverted EII could be removed with trypsin without effecting the integrity of the liposomal membrane. This enabled us to study the two different EII orientations independently. The population of inverted EII molecules was monitored by measuring active extrusion of mannitol after the addition of phosphoenolpyruvate, EI, and histidine-containing phosphocarrier protein (HPr) at the outside of the vesicles. The population of correctly oriented EII molecules was monitored by measuring active uptake of mannitol with internal phosphoenolpyruvate, EI, and HPr. A low rate of facilitated diffusion of mannitol via the unphosphorylated carrier could be measured. On the other hand, a high phosphorylation activity without translocation was observed at the outside of the liposomes. The kinetics of the phosphoenolpyruvate-dependent transport reaction and the nonvectorial phosphorylation reaction were compared. Transport of mannitol into the liposomes via the correctly oriented EII molecules occurred with a high affinity (Km, lower than 10 microM) and with a relatively low Vmax. Phosphorylation at the outside of the liposomes catalyzed by the inverted EII molecules occurred with a low affinity (Km of about 66 microM), while the maximal velocity was about 10 times faster than the transport reaction. The latter observation is kinetic proof for the lack of strict coupling between transport and phosphorylation in these enzymes.     

NMR structure of cysteinyl-phosphorylated enzyme IIB of the N,N'-diacetylchitobiose-specific phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli

The determination by NMR of the solution structure of the phosphorylated enzyme IIB (P-IIB(Chb)) of the N,N'-diacetylchitobiose-specific phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli is presented. Most of the backbone and side-chain resonances were assigned using a variety of mostly heteronuclear NMR experiments. The remaining resonances were assigned with the help of the structure calculations.NOE-derived distance restraints were used in distance geometry calculations followed by molecular dynamics and simulated annealing protocols. In addition, combinations of ambiguous restraints were used to resolve ambiguities in the NOE assignments. By combining sets of ambiguous and unambiguous restraints into new ambiguous restraints, an error function was constructed that was less sensitive to information loss caused by assignment uncertainties. The final set of structures had a pairwise rmsd of 0.59 A and 1.16 A for the heavy atoms of the backbone and side-chains, respectively.Comparing the P-IIB(Chb) solution structure with the previously determined NMR and X-ray structures of the wild-type and the Cys10Ser mutant shows that significant differences between the structures are limited to the active-site region. The phosphoryl group at the active-site cysteine residue is surrounded by a loop formed by residues 10 through 16. NOE and chemical shift data suggest that the phosphoryl group makes hydrogen bonds with the backbone amide protons of residues 12 and 15. The binding mode of the phosphoryl group is very similar to that of the protein tyrosine phosphatases. The differences observed are in accordance with the presumption that IIB(Chb) has to be more resistant to hydrolysis than the protein tyrosine phosphatases. We propose a proton relay network by which a transfer occurs between the cysteine SH proton and the solvent via the hydroxyl group of Thr16.     

Inducible phosphoenolpyruvate-dependent hexose phosphotransferase activities in Escherichia coli

1. A method is described for measuring the rate of phosphoenolpyruvate-dependent phosphotransferase activity for a variety of hexoses in toluene-treated suspensions of Escherichia coli. 2. The specific activities of the phosphotransferases that catalyse the phosphorylation of hexoses are greatly affected by the carbon source for growth. 3. In all strains of E. coli tested, fructose phosphotransferase activity is induced by growth on fructose. 4. Strains of E. coli differ greatly in the rate at which they phosphorylate glucose, but all strains possess at least a low glucose phosphotransferase activity under any tested condition of growth. Glucose phosphotransferase activity is further induced by growth on glucose; this does not occur in a mutant that lacks the ability to take up methyl alpha-d-[(14)C]glucopyranoside and hence grows poorly on glucose. 5. When growing on fructose, two strains of E. coli synthesize the inducible glucose phosphotransferase system gratuitously, and to specific activities higher than observed during growth on glucose. A phosphotransferase catalysing the phosphorylation of mannose is similarly induced.     

The NMR side-chain assignments and solution structure of enzyme IIBcellobiose of the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli.

The assignment of the side-chain NMR resonances and the determination of the three-dimensional solution structure of the C10S mutant of enzyme IIBcellobiose (IIBcel) of the phosphoenolpyruvate-dependent phosphotransferase system of Escherichia coli are presented. The side-chain resonances were assigned nearly completely using a variety of mostly heteronuclear NMR experiments, including HCCH-TOCSY, HCCH-COSY, and COCCH-TOCSY experiments as well as CBCACOHA, CBCA(CO)NH, and HBHA(CBCA)(CO)NH experiments. In order to obtain the three-dimensional structure, NOE data were collected from 15N-NOESY-HSQC, 13C-HSQC-NOESY, and 2D NOE experiments. The distance restraints derived from these NOE data were used in distance geometry calculations followed by molecular dynamics and simulated annealing protocols. In an iterative procedure, additional NOE assignments were derived from the calculated structures and new structures were calculated. The final set of structures, calculated with approximately 2000 unambiguous and ambiguous distance restraints, has an rms deviation of 1.1 A on C alpha atoms. IIBcel consists of a four stranded parallel beta-sheet, in the order 2134. The sheet is flanked with two and three alpha-helices on either side. Residue 10, a cysteine in the wild-type enzyme, which is phosphorylated during the catalytic cycle, is located at the end of the first beta-strand. A loop that is proposed to be involved in the binding of the phosphoryl-group follows the cysteine. The loop appears to be disordered in the unphosphorylated state.     

The membrane-bound domain of the phosphotransferase enzyme IImtl of Escherichia coli constitutes a mannitol translocating unit

The orientation of the mannitol binding site on the Escherichia coli phosphotransferase enzyme IImtl in the unphosphorylated state has been investigated by measuring mannitol binding to cytoplasmic membrane vesicles with a right-side-out and inside-out orientation. Enzyme IImtl is shown to catalyze facilitated diffusion of mannitol at a low rate. At equilibrium, bound mannitol is situated at the periplasmic side of the membrane. The apparent binding constant is 40 nM for the intact membranes. Solubilization of the membranes in detergent decreases the affinity by about a factor of 2. Inside-out membrane vesicles, treated with trypsin to remove the C-terminal cytoplasmic domain of enzyme IImtl, showed identical activities. These experiments indicate that the translocation of mannitol is catalyzed by the membrane-bound N-terminal half of enzyme IImtl which is a structurally stable domain.     

Dependency of sugar transport and phosphorylation by the phosphoenolpyruvate-dependent phosphotransferase system on membranous phosphatidylethanolamine in Escherichia coli: studies with a pssA mutant lacking phosphatidylserine synthase

An isogenic pair of Escherichia coli strains lacking (pssA) and possessing (wild-type) the enzyme phosphatidylserine synthase was used to estimate the effects of the total lack of phosphatidylethanolamine (PE), the major phospholipid in E. coli membranes, on the activities of several sugar permeases (enzymes II) of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). The mutant exhibits greatly elevated levels of phosphatidylglycerol (PG), a lipid that has been reported to stimulate the in vitro activities of several PTS permeases. The activities, thermal stabilities, and detergent sensitivities of three PTS permeases, the glucose enzyme II (II^Glc), the mannose enzyme II (II^Man) and the mannitol enzyme II (II^Mtl), were characterized. Western blot analyses revealed that the protein levels of II^Glc were not appreciably altered by the loss of PE. In the pssA mutant, II^Glc and II^Man activities were depressed both in vivo and in vitro, with the in vivo transport activities being depressed much more than the in vitro phosphorylation activities. II^Mtl also exhibited depressed transport activity in vivo but showed normal phosphorylation activities in vitro. II^Man and II^Glc exhibited greater thermal lability in the pssA mutant membranes than in the wild-type membranes, but II^Mtl showed enhanced thermal stability. All three enzymes were activated by exposure to TritonX100 (0.4%) or deoxycholate (0.2%) and inhibited by SDS (0.1%), but II^Mtl was the least affected. II^Man and, to a lesser degree, II^Glc were more sensitive to detergent treatments in the pssA mutant membranes than in the wild-type membranes while II^Mtl showed no differential effect. The results suggest that all three PTS permeases exhibit strong phospholipid dependencies for transport activity in vivo but much weaker and differential dependencies for phosphorylation activities in vitro, with II^Man exhibiting the greatest and II^Mtl the least dependency. The effects of lipid composition on thermal sensitivities and detergent activation responses paralleled the effects on in vitro phosphorylation activities. These results together with those previously published suggest that, while the in vivo transport activities of all PTS enzymes II require an appropriate anionic to zwitterionic phospholipid balance, the in vitro phosphorylation activities of these same enzymes show much weaker and differential dependencies. Alteration of the phospholipid composition of the membrane thus allows functional dissection of transport from the phosphorylation activities of PTS enzyme complexes.     

Enzyme II of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system: protein-protein and protein-phospholipid interactions

The mannitol-specific enzyme II (EII), purified free of phospholipid, exhibits a concentration dependence in its specific activity with P-HPr and mannitol as the donor and acceptor substrates, respectively. This concentration dependence, previously observed only in the case of mannitol----mannitol phosphate exchange reaction, indicates that an oligomeric form of the enzyme is responsible for catalyzing the phosphorylation reaction (P-HPr + mannitol----mannitol-P + HPr) as well as the exchange reaction. Kinetic analysis revealed that the monomeric enzyme has a much lower specific activity than the associated species. The specific activity can be increased by raising the steady-state level of phosphorylation of EII and also by adding phospholipid, demonstrating that phosphorylation and the binding of phospholipid facilitate the association process. Kinetic measurements and fluorescence energy transfer measurements demonstrate a strong preference of EII for phospholipids with specific head group and fatty acid composition.     

Role of the phosphoenolpyruvate-dependent fructose phosphotransferase system in the utilization of mannose by Escherichia coli.

Mutants of Escherichia coli devoid of the membrane-spanning proteins PtsG and PtsMP, which are components of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) and which normally effect the transport into the cells of glucose and mannose, do not grow upon or take up either sugar. Pseudorevertants are described that take up, and grow upon, mannose at rates strongly dependent on the mannose concentration in the medium (apparent Km > 5 mM); such mutants do not grow upon glucose but are derepressed for the components of the fructose operon. Evidence is presented that mannose is now taken up via the fructose-PTS to form mannose 6-phosphate, which is further utilized for growth via fructose 6-phosphate and fructose 1,6-bisphosphate.     

Mannitol-specific enzyme II of the phosphoenolpyruvate-dependent phosphotransferase system of Staphylococcus carnosus. Sequence and expression in Escherichia coli and structural comparison with the enzyme IImannitol of Escherichia coli.

The enzyme IImannitol (EIImtl) of the phosphoenolpyruvate-dependent phosphotransferase system (PTS) catalyses the uptake and concomitant phosphorylation of mannitol by bacteria; it is specified by the gene mtlA. MtlA is located near the genes mtlF and mtlD in the staphylococcal genome, encoding the enzyme IIImtl and the mannitol-1-phosphate dehydrogenase, respectively. We present the cloning of the whole operon by a novel complementation system which is generally suitable for cloning Gram-positive PTS genes. The nucleotide sequence of a 2.5-kbp subclone spanning mtlA has been determined. From the deduced amino acid sequence, it is predicted that the membrane-protein EIImtl consists of 505 amino acid residues (54112 Da). The protein has the expected hydropathy profile of an integral-membrane protein. The NH2-terminal part of the enzyme resides within the membrane, whereas the COOH-terminus of the enzyme has the properties of a soluble protein. Comparison with the known amino acid sequence of EIImtl of Escherichia coli [Lee, C. A. & Saier, M. H. (1983) J. Biol. Chem. 258, 10761-10767] showed significant similarity. The motif containing the cysteine, which is the putative second phosphorylation site in EIImtl of E. coli [Pas, H. H. & Robillard, G. T. (1988) Biochemistry 27, 5835-5839], is well conserved in EIImtl of Staphylococcus carnosus. Chemical modification of the single active site cysteine residue by Ellman's reagent leads to total inactivation, which can be reversed by treatment with 2-mercaptoethanol.     

Stimulation of dihydroxyacetone and glycerol kinase activity in Streptococcus faecalis by phosphoenolpyruvate-dependent phosphorylation catalyzed by enzyme I and HPr of the phosphotransferase system.

Recently we reported the phosphoenolpyruvate (PEP)-dependent phosphorylation of a 55-kilodalton protein of Streptococcus faecalis catalyzed by enzyme I and histidine-containing protein (HPr) of the phosphotransferase system (J. Deutscher, FEMS Microbiol. Lett. 29:237-243, 1985). The purified 55-kilodalton protein was found to exhibit dihydroxyacetone kinase activity. Glycerol was six times more slowly phosphorylated than dihydroxyacetone. The Kms were found to be 0.7 mM for ATP, 0.45 mM for dihydroxyacetone, and 0.9 mM for glycerol. PEP-dependent phosphorylation of dihydroxyacetone kinase stimulated phosphorylation of both substrates about 10-fold. Fructose 1,6-diphosphate at concentrations higher than 2 mM inhibited the activity of phosphorylated and unphosphorylated dihydroxyacetone kinase in a noncompetitive manner. The rate of PEP-dependent phosphorylation of dihydroxyacetone kinase was about 200-fold slower than the phosphorylation rate of III proteins (also called enzyme III or factor III), which so far have been considered the only phosphoryl acceptors of histidyl-phosphorylated HPr. P-Dihydroxyacetone kinase was found to be able to transfer its phosphoryl group in a backward reaction to HPr. Following [32P]PEP-dependent phosphorylation and tryptic digestion of dihydroxyacetone kinase, we isolated a labeled peptide composed of 37 amino acids, as determined by amino acid analysis. The single histidyl residue of this peptide most likely carries the phosphoryl group in phosphorylated dihydroxyacetone kinase.