Analog Of Phosphoenolpyruvate Research Articles

The Impact of Fosfomycin on Gram Negative Infections: A Comprehensive Review.

Multidrug-resistant or extended drug resistance has created havoc when it comes to patient treatment, as options are limited because of the spread of pathogens that are extensively or multidrug-resistant (MDR or XDR) and the absence of novel antibiotics that are effective against these pathogens. Physicians have therefore started using more established antibiotics such as polymyxins, tetracyclines, and aminoglycosides. Fosfomycin has just come to light as a result of the emergence of resistance to these medications since it continues to be effective against MDR and XDR bacteria that are both gram-positive and gram-negative. Fosfomycin, a bactericidal analogue of phosphoenolpyruvate that was formerly utilised as an oral medication for uncomplicated urinary tract infections, has recently attracted the interest of clinicians around the world. It may generally be a suitable therapy option for patients with highly resistant pathogenic infections, according to the advanced resistance shown by gram-negative bacteria. This review article aims to comprehensively evaluate the impact of fosfomycin on gram negative infections, highlighting its mechanism of action, pharmacokinetics, clinical efficacy, and resistance patterns.

Overexpression of improved EPSPS gene results in field level glyphosate tolerance and higher grain yield in rice.

SummaryGlyphosate is a popular, systemic, broad‐spectrum herbicide used in modern agriculture. Being a structural analog of phosphoenolpyruvate (PEP), it inhibits 5‐enolpyruvylshikimate 3‐phosphate synthase (EPSPS) which is responsible for the biosynthesis of aromatic amino acids and various aromatic secondary metabolites. Taking a lead from glyphosate‐resistant weeds, two mutant variants of the rice EPSPS gene were developed by amino acid substitution (T173I + P177S; TIPS‐OsEPSPS and G172A + T173I + P177S; GATIPS‐OsEPSPS). These mutated EPSPS genes were overexpressed in rice under the control of either native EPSPS or constitutive promoters (maize ubiquitin [ZmUbi] promoter). The overexpression of TIPS‐OsEPSPS under the control of the ZmUbi promoter resulted in higher tolerance to glyphosate (up to threefold of the recommended dose) without affecting the fitness and related agronomic traits of plants in both controlled and field conditions. Furthermore, such rice lines produced 17%–19% more grains compared to the wild type (WT) in the absence of glyphosate application and the phenylalanine and tryptophan contents in the transgenic seeds were found to be significantly higher in comparison with WT seeds. Our results also revealed that the native promoter guided expression of modified EPSPS genes did not significantly improve the glyphosate tolerance. The present study describing the introduction of a crop‐specific TIPS mutation in class I aroA gene of rice and its overexpression have potential to substantially improve the yield and field level glyphosate tolerance in rice. This is the first report to observe that the EPSPS has role to play in improving grain yield of rice.

614. Metabolic Interventions for the Resensitization of Daptomycin-Resistant (DAP-R) Streptococcus mitis-oralis Strains to DAP In vitro and Ex Vivo in a Simulated Model of Experimental Endocarditis (IE)

Background Streptococcus mitis-oralis is a leading cause of IE. Treatment of this pathogen is limited by frequent high-level β-lactam resistance and the propensity to develop high-level DAP-R during DAP exposure. The current study elucidated key metabolic perturbations associated with high-level DAP-R in prototype S. mitis-oralis strain 351, following in vitro selection of DAP-R by 10-day serial passage in sub-inhibitory DAP. Furthermore, to test translatability of such metabolic changes (see below), the synergistic activity of combinations of DAP plus a strategic metabolic inhibitor (i.e., fosfomycin) vs. DAP or fosfomycin alone was assessed, using DAP-R S. mitis-oralis strain 351-D10 (MIC >256 µg/mL) in vitro and in an ex vivo IE model.MethodsMICs. E test Growth Curve: Optical density (OD600) determined spectrophotometrically at 0–8 hours glyceraldehyde-3-phosphatedehydrogenase (GAPDH) activity. Kit from BioVision®. Metabolomics: one-dimensional 1H NMR-MS and two-dimensional 1H-13C HSQC in vitro time-kill assay: Using sub-MIC/MIC drug concentrations (initial inoculum ~1 × 105 CFU/mL) for 0, 2, 4, 6, and 8 hours. Ex vivo IE model: Simulated endocardial vegetations (SEVs) quantitatively cultured at 0, 4, 8, 24, 32, 48, and 72 hours with DAP or fosfomycin alone or in combination.ResultsNMR metabolomics analysis identified a number of metabolite differences in the 351 D10 DAP-R vs. 351 DAP-S strain (Figure 1). These data are consistent with a significant reduction in GAPDH activity (a glycolytic enzyme) in 351-D10 vs. 351 strain. Based on these metabolic changes, fosfomycin (a phosphoenolpyruvate analog) was chosen as a strategic metabolic inhibitor to attempt to “resensitize” our DAP-R S. mitis-oralis strain to DAP. The combination of DAP + fosfomycin demonstrated synergistic killing of the DAP-R strain vs. DAP or fosfomycin alone in the in vitro time-killing assays. Moreover, the DAP-R strain was synergistically cleared from SEVs by DAP + fosfomycin in the ex vivo IE model.ConclusionTaken together, these data indicate there are unique metabolome signatures associated with the DAP-R phenotype in S. mitis-oralis. In addition, these data provide support for further studying the use of strategic S. mitis-oralis metabolic inhibitors in additional strain-sets to resensitize DAP-R strains to DAP, using in vitro, ex vivo and in vivo models. Disclosures All authors: No reported disclosures.

Expression patterns of cp4-epsps gene in diverse transgenic Saccharum officinarum L. genotypes.

Glyphosate, a functional analogue of phosphoenolpyruvate (PEP), blocks the shikimate pathway by inhibiting the enzyme5-enolpyruvylshikimate-3-phosphate synthase (EPSPS; EC 2.5.1.19) through interference with the conversion of (shikimate-3-phosphate) S3P and PEP to 5-enolpyruvylshikimate-3-phosphate (EPSP) and subsequently leads to plant death. This metabolic pathway possesses great potential to be used for development of herbicide resistant transgenic crops and here in this study, we wanted to check the expression potential of CP4-EPSPS gene in various sugarcane genotypes. A synthetic version of CP4-EPSPS gene synthesized commercially, cloned in pGreen0029 vector, was transformed into regenerable embryogenic calli of three different sugarcane cultivars HSF-240, S2003US-778 and S2003US-114 using biolistic gene transfer approach for comparative transcriptional studies. Transgenic lines screened by PCR analysis were subjected to Southern hybridization for checking transgene integration patterns. All the tested lines were found to contain multiple (3-6) insert copies. Putative transgenic plants produced the CP4-EPSPS protein which was detected using immunoblot analysis. The CP4-EPSPS transcript expression detected by qRT-PCR was found to vary from genotype to genotype and is being reported first time. In vitro glyphosate assay showed that transformed plants were conferring herbicide tolerance. It is concluded that different cultivars of sugarcane give variable expression of the same transgene and reasons for this phenomenon needs to be investigated.

Mutants of an electrogenic bacterium Shewanella oneidensis MR-1 with increased reducing activity

The mutants of Shewanella oneidensis MR-1 resistant to fosfomycin, a toxic analogue of phosphoenolpyruvate, were obtained. The mutants exhibited increased reducing activity and higher rates of lactate utilization. A correlation was shown between the rates of metabolism of oxidized substrates and the rate of reduction of methylene blue, a mediator of electron transport. The mutants of S. oneidensis MR-1 may be used in microbial fuel cells for intensification of energy production from organic compounds.

Identification of a novel UDP-N-acetylglucosamine enolpyruvyl transferase (MurA) from Vibrio fischeri that confers high fosfomycin resistance in Escherichia coli

MurA [UDP-N-acetylglucosamine (UDP-NAG) enolpyruvyl transferase] is a key enzyme involved in bacterial cell wall peptidoglycan synthesis and a target for the antimicrobial agent fosfomycin, a structural analog of the MurA substrate phosphoenol pyruvate. In this study, we identified, cloned and sequenced a novel murA gene from an environmental isolate of Vibrio fischeri that is naturally resistant to fosfomycin. The fosfomycin resistance gene was isolated from a genomic DNA library of V. fischeri. An antimicrobial agent hypersensitive strain of Escherichia coli harboring murA from V. fischeri exhibited a high fosfomycin resistance phenotype, with minimum inhibitory concentration of 3,000 microg/ml. The cloned murA gene was 1,269 bp long encoding a 422 amino acid polypeptide with an estimated pI of 5.0. The deduced amino acid sequence of the putative protein was identified as UDP-NAG enolpyruvyl transferase by homology comparison. The MurA protein with an estimated molecular weight of 44.7 kDa was expressed in E. coli and purified by affinity chromatography. MurA of V. fischeri will be a useful target to identify potential inhibitors of fosfomycin resistance in pharmacological studies.

Stereochemistry of the carboxylation reaction catalyzed by the ATP-dependent phosphoenolpyruvate carboxykinases from Saccharomyces cerevisiae and Anaerobiospirillum succiniciproducens

The stereochemistry of CO 2 addition to phosphoenolpyruvate (PEP) to yield oxaloacetate catalyzed by ATP-dependent Saccharomyces cerevisiae and Anaerobiospirillum succiniciproducens PEP carboxykinases was determined using (Z)-3-fluorophosphoenolpyruvate ((Z)-F-PEP) as a substrate analog. A. succiniciproducens and S. cerevisiae PEP carboxykinases utilized (Z)-F-PEP with 1/14 and 1/47 the respective K m values for PEP. On the other hand, in the bacterial and yeast enzymes k cat was reduced to 1/67 and 1/48 the value with PEP, respectively. The binding affinity of pyridoxylphosphate-labeled S. cerevisiae and A. succiniciproducens PEP carboxykinases for PEP and (Z)-F-PEP was checked and found to be of similar magnitude for both substrates, suggesting that the lowered K m values for the fluorine-containing PEP analog are due to kinetic effects. The lowered k cat values when using (Z)-F-PEP as substrate suggest that the electron withdrawing effect of fluorine affects the nucleophilic attack of the double bond of (Z)-F-PEP to CO 2. For the stereochemical analyses, the carboxylation of (Z)-F-PEP was coupled to malate dehydrogenase to yield 3-fluoromalate, which was analyzed by 19F NMR. The fluoromalate obtained was identified as (2 R, 3 R)-3-fluoromalate for both the A. succiniciproducens and S. cerevisiae PEP carboxykinases, thus indicating that CO 2 addition to (Z)-F-PEP, and hence PEP, takes place through the 2- si face of the double bond. These results, together with previously published data [Rose, I.A. et al. J. Biol. Chem. 244 (1969) 6130–6133; Hwang, S.H. and Nowak, T. Biochemistry 25 (1986) 5590–5595] indicate that PEP carboxykinases, no matter their nucleotide specificity, catalyze the carboxylation of PEP from the 2- si face of the double bond.

The Molecular Basis of Glyphosate Resistance by an Optimized Microbial Acetyltransferase

GAT is an N-acetyltransferase from Bacillus licheniformis that was optimized by gene shuffling for acetylation of the broad spectrum herbicide, glyphosate, forming the basis of a novel mechanism of glyphosate tolerance in transgenic plants (Castle, L. A., Siehl, D. L., Gorton, R., Patten, P. A., Chen, Y. H., Bertain, S., Cho, H. J., Duck, N., Wong, J., Liu, D., and Lassner, M. W. (2004) Science 304, 1151-1154). The 1.6-A resolution crystal structure of an optimized GAT variant in ternary complex with acetyl coenzyme A and a competitive inhibitor, 3-phosphoglyerate, defines GAT as a member of the GCN5-related family of N-acetyltransferases. Four active site residues (Arg-21, Arg-73, Arg-111, and His-138) contribute to a positively charged substrate-binding site that is conserved throughout the GAT subfamily. Structural and kinetic data suggest that His-138 functions as a catalytic base via substrate-assisted deprotonation of the glyphosate secondary amine, whereas another active site residue, Tyr-118, functions as a general acid. Although the physiological substrate is unknown, native GAT acetylates D-2-amino-3-phosphonopropionic acid with a kcat/Km of 1500 min-1 mM-1. Kinetic data show preferential binding of short analogs to native GAT and progressively better binding of longer analogs to optimized variants. Despite a 200-fold increase in kcat and a 5.4-fold decrease in Km for glyphosate, only 4 of the 21 substitutions present in R7 GAT lie in the active site. Single-site revertants constructed at these positions suggest that glyphosate binding is optimized through substitutions that increase the size of the substrate-binding site. The large improvement in kcat is likely because of the cooperative effects of additional substitutions located distal to the active site.

Itaconate reduces visceral fat by inhibiting fructose 2,6-bisphosphate synthesis in rat liver

Objective Itaconate is an analog of phospho enolpyruvate, which is an inhibitor of fructose-6-phosphate 2-kinase (F6P2Kinase), an enzyme that synthesizes fructose 2,6-bisphosphate (F26BP). Carbohydrates ingested are preferentially used for glycogen synthesis in the liver and muscles, and excess carbohydrates are metabolized by glycolysis in the liver and used for fatty acid synthesis. We hypothesized that itaconate is incorporated into liver cells and suppresses fat synthesis by inhibiting liver glycolysis at the step of phosphofructokinase, which is activated by F26BP. Methods Rats were allowed to eat ad libitum for 3 wk or, in separate experiments, to limit food intake by pair feeding. One group was given drinking water (control group) and the other group was given a 10 g/L itaconate solution (itaconate group). We measured body weight gain, visceral fat accumulation, and F6P2Kinase activity. Results Body weight gain in the itaconate group was lower than that in the control group ( P < 0.05). In the dietary-controlled rats, there was no difference in body weight increase between groups, but visceral fat content ( P < 0.01), plasma free fatty acid, and triacylglycerol levels ( P < 0.05) were lower in the itaconate group than in the control group. Further, itaconate decreased the F26BP level ( P < 0.05) in vivo and partly inhibited rat liver-type F6P2Kinase in vitro. Conclusions These results indicate that itaconate, which is a decarboxylate and resembles phospho enolpyruvate, is incorporated into liver cells and suppresses glycolysis by decreasing the level of F26BP, resulting in decreased visceral fat.

Phospho enolpyruvate carboxylase: three-dimensional structure and molecular mechanisms

Phospho enolpyruvate carboxylase (PEPC; EC 4.1.1.31) catalyzes the irreversible carboxylation of phospho enolpyruvate (PEP) to form oxaloacetate and Pi using Mg 2+ or Mn 2+ as a cofactor. PEPC plays a key role in photosynthesis by C4 and Crassulacean acid metabolism plants, in addition to its many anaplerotic functions. Recently, three-dimensional structures of PEPC from Escherichia coli and the C4 plant maize ( Zea mays) were elucidated by X-ray crystallographic analysis. These structures reveal an overall square arrangement of the four identical subunits, making up a “dimer-of-dimers” and an eight-stranded β barrel structure. At the C-terminal region of the β barrel, the Mn 2+ and a PEP analog interact with catalytically essential residues, confirmed by site-directed mutagenesis studies. At about 20 Å from the β barrel, an allosteric inhibitor (aspartate) was found to be tightly bound to down-regulate the activity of the E. coli enzyme. In the case of maize C4-PEPC, the putative binding site for an allosteric activator (glucose 6-phosphate) was also revealed. Detailed comparison of the various structures of E. coli PEPC in its inactive state with maize PEPC in its active state shows that the relative orientations of the two subunits in the basal “dimer” are different, implicating an allosteric transition. Dynamic movements were observed for several loops due to the binding of either an allosteric inhibitor, a metal cofactor, a PEP analog, or a sulfate anion, indicating the functional significance of these mobile loops in catalysis and regulation. Information derived from these three-dimensional structures, combined with related biochemical studies, has established models for the reaction mechanism and allosteric regulation of this important C-fixing enzyme.

Enzyme I of the phosphotransferase system: induced-fit protonation of the reaction transition state by Cys-502.

Enzyme I (EI), the first component of the phosphoenolpyruvate (PEP):sugar phosphotransferase system (PTS), consists of an N-terminal domain with the phosphorylation site (His-189) and a C-terminal domain with the PEP binding site. Here we use C3-substituted PEP analogues as substrates and inhibitors and the EI(C502A) mutant to characterize structure-activity relationships of the PEP binding site. EI(C502A) is 10 000 times less active than wild-type EI [EI(wt)] with PEP as the substrate, whereas the two forms are equally active with ZClPEP. Cys-502 acts as an acid-base catalyst which stereospecifically protonates the pyruvoyl enolate at C3. The electron-withdrawing chlorine of ZClPEP can compensate for the lack of Cys-502, and in this case, the released 3-Cl-enolate is protonated nonstereospecifically. Several PEP analogues were assayed as inhibitors and as substrates. The respective K(I)/K(m) ratios vary between 3 and 40 for EI(wt), but they are constant and around unity for EI(C502A). EI(wt) with PEP as the substrate is inhibited by oxalate, whereas EI(C502A) with ZClPEP is not. The different behavior of EI(wt) and EI(C502A) toward the PEP analogues and oxalate suggests that the PEP binding site of EI(wt) exists in a "closed" and an "open" form. The open to closed transition is triggered by the interaction of the substrate with Cys-502. The closed conformation is sterically disfavored by C3-modified substrate analogues such as ZClPEP and ZMePEP. If site closure does not occur as with EI(C502A) and bulky substrates, the transition state is stabilized by electron dispersion to the electron-withdrawing substituent at C3.

Structure-Based Design of Novel Inhibitors of 3-Deoxy-d-manno-octulosonate 8-Phosphate Synthase

3-Deoxy-D-manno-octulosonate 8-phosphate (KDO8P) is the phosphorylated precursor of KDO, an essential sugar of the lipopolysaccharide of Gram negative bacteria. KDO8P is produced by a specific synthase (KDO8PS) by condensing arabinose 5-phosphate (A5P) and phosphoenolpyruvate (PEP), with release of inorganic phosphate. As KDO8PS is present in bacteria and plants, but not in mammalian cells, and mutations that inactivate KDO8PS also block cell replication, KDO8PS is a promising target for the design of new antimicrobials that act by blocking lipopolysaccharide biosynthesis. Previous studies have shown that a compound mimicking an intermediate of the condensation reaction is a good ligand and a powerful inhibitor. Here we report on the crystallographic investigation of the binding to KDO8PS of new derivatives of this original inhibitor. The structures of the enzyme in complex with these compounds, and also with the PEP analogs, 2-phosphoglyceric acid (2-PGA) and Z-methyl-PEP, point to future strategies for the design of novel inhibitors of KDO8PS.

Crystal Structures of C 4 Form Maize and Quaternary Complex of E. coli Phosphoenolpyruvate Carboxylases

Phosphoenolpyruvate carboxylase (PEPC) catalyzes the first step in the fixation of atmospheric CO 2 during C 4 photosynthesis. The crystal structure of C 4 form maize PEPC (ZmPEPC), the first structure of the plant PEPCs, has been determined at 3.0 Å resolution. The structure includes a sulfate ion at the plausible binding site of an allosteric activator, glucose 6-phosphate. The crystal structure of E. coli PEPC (EcPEPC) complexed with Mn 2+, phosphoenolpyruvate analog (3,3-dichloro-2-dihydroxyphosphinoylmethyl-2-propenoate), and an allosteric inhibitor, aspartate, has also been determined at 2.35 Å resolution. Dynamic movements were found in the ZmPEPC structure, compared with the EcPEPC structure, around two loops near the active site. On the basis of these molecular structures, the mechanisms for the carboxylation reaction and for the allosteric regulation of PEPC are proposed.

Synthesis of phosphoenol pyruvate (PEP) analogues and evaluation as inhibitors of PEP-utilizing enzymes.

The synthesis of 10 new phosphoenolpyruvate (PEP) analogues with modifications in the phosphate and the carboxylate function is described. Included are two potential irreversible inhibitors of PEP-utilizing enzymes. One incorporates a reactive chloromethylphosphonate function replacing the phosphate group of PEP. The second contains a chloromethyl group substituting for the carboxylate function of PEP. An improved procedure for the preparation of the known (Z)- and (E)-3-chloro-PEP is also given. The isomers were obtained as a 4 : 1 mixture, resolved by anion-exchange chromatography after the last reaction step. The stereochemistry of the two isomers was unequivocally assigned from the (3)J(H-C) coupling constants between the carboxylate carbons and the vinyl protons. All of these and other known PEP-analogues were tested as reversible and irreversible inhibitors of Mg2+- and Mn2+- activated PEP-utilizing enzymes: enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), pyruvate kinase, PEP carboxylase and enolase. Without exception, the most potent inhibitors were those with substitution of a vinyl proton. Modification of the phosphate and the carboxylate groups resulted in less effective compounds. Enzyme I was the least tolerant to such modifications. Among the carboxylate-modified analogues, only those replaced by a negatively charged group inhibited pyruvate kinase and enolase. Remarkably, the activity of PEP carboxylase was stimulated by derivatives with neutral groups at this position in the presence of Mg2+, but not with Mn2+. For the irreversible inhibition of these enzymes, (Z)-3-Cl-PEP was found to be a very fast-acting and efficient suicide inhibitor of enzyme I (t(1/2) = 0.7 min).

Synthesis of phosphoenol pyruvate (PEP) analogues and evaluation as inhibitors of PEP‐utilizing enzymes

The synthesis of 10 new phosphoenolpyruvate (PEP) analogues with modifications in the phosphate and the carboxylate function is described. Included are two potential irreversible inhibitors of PEP‐utilizing enzymes. One incorporates a reactive chloromethylphosphonate function replacing the phosphate group of PEP. The second contains a chloromethyl group substituting for the carboxylate function of PEP. An improved procedure for the preparation of the known (Z)‐ and (E)‐3‐chloro‐PEP is also given. The isomers were obtained as a 4 : 1 mixture, resolved by anion‐exchange chromatography after the last reaction step. The stereochemistry of the two isomers was unequivocally assigned from the 3JH‐C coupling constants between the carboxylate carbons and the vinyl protons.All of these and other known PEP‐analogues were tested as reversible and irreversible inhibitors of Mg2+‐ and Mn2+‐ activated PEP‐utilizing enzymes: enzyme I of the phosphoenolpyruvate:sugar phosphotransferase system (PTS), pyruvate kinase, PEP carboxylase and enolase. Without exception, the most potent inhibitors were those with substitution of a vinyl proton. Modification of the phosphate and the carboxylate groups resulted in less effective compounds. Enzyme I was the least tolerant to such modifications. Among the carboxylate‐modified analogues, only those replaced by a negatively charged group inhibited pyruvate kinase and enolase. Remarkably, the activity of PEP carboxylase was stimulated by derivatives with neutral groups at this position in the presence of Mg2+, but not with Mn2+. For the irreversible inhibition of these enzymes, (Z)‐3‐Cl‐PEP was found to be a very fast‐acting and efficient suicide inhibitor of enzyme I (t1/2 = 0.7 min).

Fosfomycin: A Review

FOSFOMYCIN WAS NOT mentioned as a therapeutic option for the treatment of urinary tract infections (UTIs) in the latest editions of two major textbooks of infectious diseases [1,2], despite the fact that it has been available in the United States for 4 years. It has been a commonly prescribed antibiotic in Japan and many parts of Europe for 2 decades. Fosfomycin was listed as a potentially useful antibiotic for the treatment of uncomplicated cystitis in an earlier review [3]. Currently, it has the approval of the U.S. Food and Drug Administration for the treatment of adult women with uncomplicated UTIs that are caused by Escherichia coli and Enterococcus faecalis. These introductory facts prompted this review of fosfomycin. We believe this discussion will be useful to practicing clinicians, especially those in the fields of internal medicine, gynecology, urology, and infectious diseases. Fosfomycin trometamol was first described in 1969 [4]. It is a phosphonic acid derivative, which acts primarily by interfering with bacterial peptidoglycan synthesis, thereby disrupting cell wall synthesis [5]. It has a broad spectrum of activity against aerobic bacteria, including those that cause UTIs [6]. There seems to be little cross-resistance between fosfomycin and other antibiotics commonly used to treat UTIs; thus, its efficacy is not affected by development of resistance to other antibiotics. It can be administered orally with a convenient dosing schedule, including single-dose therapy for uncomplicated cystitis.

Reevaluation of the accepted allosteric mechanism of phosphofructokinase from Bacillus stearothermophilus

The binding of phosphoenolpyruvate (PEP) to the single allosteric site on phosphofructokinase (EC ) from Bacillus stearothermophilus (BsPFK) diminishes the ability of the enzyme to bind the substrate fructose 6-phosphate (Fru-6-P). Comparisons of crystal structures with either Fru-6-P or phosphoglycolate, an analog of PEP, bound have shown that Arg-162 interacts with the negatively charged Fru-6-P. Upon the binding of phosphoglycolate, Arg-162 is virtually replaced by Glu-161, which introduces a potential coulombic repulsion between enzyme and substrate [Schirmer, T. & Evans, P. R. (1990) Nature (London) 343, 140-145]. It has previously been proposed that this structural transition explains the allosteric inhibition in BsPFK, and this explanation has appeared in textbooks to illustrate how an allosteric ligand can influence substrate binding at a distance. Site-directed mutagenesis has been employed to create three mutants of BsPFK that substitute an alanine residue for Glu-161, Arg-162, or both. The E161A mutation does not affect the inhibition of BsPFK by PEP at 25 degrees C, and while the R162A mutation decreases BsPFK's affinity for Fru-6-P by approximately 30-fold, R162A diminishes the effectiveness of PEP inhibition by only 1/3. Combining E161A and R162A produces behavior comparable to R162A alone. These and other data suggest that the movement of Glu-161 and Arg-162 does not play the central role in producing the allosteric inhibition by PEP as originally envisioned in the Schirmer and Evans mechanism.

Overexpression, Purification, and Use of Phosphoenol Pyruvate Synthetase in the Synthesis of PEP Analogues

TheEscherichia colienzyme phosphoenol pyruvate synthetase has been overexpressed and purified in a single chromatographic step. The enzyme catalyzes the synthesis of phosphoenol pyruvate (PEP), from adenosine triphosphate and pyruvate, and has enabled the synthesis of uniformly labeled [1,2,3-13C3]PEP, which is a key molecule in structural and mechanistic studies of enolpyruvyl transferases. Fluoropyruvate was also used as substrate for the enzyme and gave only (Z)-phoephoenol-3-fluoropyruvate, albeit at a slower rate.

Studies of the allosteric properties of maize leaf phosphoenolpyruvate carboxylase with the phosphoenolpyruvate analog phosphomycin as activator

The antibiotic phosphomycin (1,2-epoxypropylphosphonic acid), an analog of phosphoenolpyruvate (PEP), behaved not as an inhibitor, but as an activator, of the enzyme phosphoenolpyruvate carboxylase (PEPC) from maize leaves. Multiple activation studies indicated that the analog binds to the Glc6P-allosteric site producing a more activated enzyme than Glc6P itself. Because of this, we used phosphomycin as a tool to further extend our understanding of the mechanisms of allosteric regulation of C 4-PEPC. Initial velocity data from detailed kinetic studies, in which the concentrations of free and Mg-complexed PEP and phosphomycin were controlled, are consistent with: (1) the true activator is free phosphomycin, which competes with free PEP for the Glc6P-allosteric site; and (2) the Mg-phosphomycin complex caused inhibition by binding to the active site in competition with MgPEP. Therefore, although the Glc6P-allosteric site and the active site are able to bind the same ligands, they differ in the form of substrate and activator they bind. This important difference allows the full expression of the potential of activation and prevents inhibition by the activators, including the physiological ones, which are mostly uncomplexed at physiological free Mg 2+ concentrations. At fixed low substrate concentrations, the saturation kinetics of the enzyme by phosphomycin showed positive cooperativity at pH 7.3 and 8.3, although at the latter pH, the kinetics of saturation by the substrate was hyperbolic. The cosolute glycerol greatly increased the affinity of the enzyme for phosphomycin and abolished the cooperativity in its binding, but did not eliminate the heterotropic effects of the activator. Therefore, the heterotropic and homotropic effects of the activator are not always coupled to the homotropic effects of the substrate, which argues against the two-state model previously proposed to explain the allosteric properties of maize-leaf PEPC.

Fosfomycin Biosynthesis and Self-Resistance Mechanism of the Producing Organism Streptomyces wedmorensis.

Fosfomycin (FM, Fig. 1) is a medically important antibiotic produced by various species of Streptomyces1) as well as Pseudomonas syringae PB-51232) and Ps. viridiflava PK-53). FM is characterized by unique structural functions such as a carbon-phosphorus (C-P) bond and an epoxide4). Acting as an analog of phosphoenolpyruvate, it irreversibly inhibits phosphoenolpyruvate UDP-N-acetylglucosamine-3-O-enolpyruvyltransferase (enolpyruvyltransferase), the enzyme that catalyzes the first step of peptidoglycan biosynthesis, and shows almost no toxicity to humans5). We review here FM biosynthesis and self-resistance, and the biosynthetic genes in S. wedmorensis.