Rich Organic Nitrogen Impacts Clavulanic Acid Biosynthesis through the Arginine Metabolic Pathway in Streptomyces clavuligerus F613-1

Clavulanic acid (CA) is the preferred clinical drug for the treatment of infections by β-lactam antibiotic-resistant bacteria. CA is produced by Streptomyces clavuligerus, and although there have been many reports on the effects of carbon and nitrogen sources on CA production, the mechanisms involved remain unclear. In this study, we found that CA accumulation in S. clavuligerus F613-1 was increased significantly in MH medium, which is rich in organic nitrogen, compared with that in ML medium, which contains half the amount of organic nitrogen present in MH medium. Transcriptome analysis revealed that genes involved in CA biosynthesis, such as ceas1, ceas2, bls1, bls2, cas2, pah2, gcaS, and cad, and arginine biosynthesis, such as argB, argC, argD, argG, argH, argJ, and argR, were upregulated under rich organic nitrogen. Metabolome data revealed notable differences between cultures of F613-1 grown in MH and ML media with regard to levels of key intracellular metabolites, most of which are involved in arginine metabolic pathways, including arginine, glutamine, and glutamic acid. Additionally, supplementation of ML medium with arginine, glutamine, or glutamic acid resulted in increased CA production by S. clavuligerus F613-1. Our results indicate that rich organic nitrogen mainly affects CA biosynthesis by increasing the levels of amino acids associated with the arginine metabolic pathway and activating the expression of the CA biosynthetic gene cluster. These findings provide important insights for improving medium optimization and engineering of S. clavuligerus F613-1 for high-yield production of CA. IMPORTANCE The bacterium Streptomyces clavuligerus is used for the industrial production of the broad-spectrum β-lactamase inhibitor clavulanic acid (CA). However, much remains unknown about the factors which affect CA yields. We investigated the effects of different levels of organic nitrogen on CA production. Our analyses indicate that higher organic nitrogen levels were associated with increased CA yields and increased levels of arginine biosynthesis. Further analyses supported the relationship between arginine metabolism and CA production and demonstrated that increasing the levels of arginine or associated amino acids could boost CA yields. These findings suggest approaches for improving the production of this clinically important antibiotic.

Linear Copolymers Based on Choline Ionic Liquid Carrying Anti-Tuberculosis Drugs: Influence of Anion Type on Physicochemical Properties and Drug Release

In this study, drug nanocarriers were designed using linear copolymers with different contents of cholinium-based ionic liquid units, i.e., [2-(methacryloyloxy)ethyl]trimethylammonium chloride (TMAMA/Cl: 25, 50, and 75 mol%). The amphiphilicity of the copolymers was evaluated on the basis of their critical micelle concentration (CMC = 0.055–0.079 mg/mL), and their hydrophilicities were determined by water contact angles (WCA = 17°–46°). The chloride anions in the polymer chain were involved in ionic exchange reactions to introduce pharmaceutical anions, i.e., p-aminosalicylate (PAS⁻), clavulanate (CLV⁻), piperacillin (PIP⁻), and fusidate (FUS⁻), which are established antibacterial agents for treating lung and respiratory diseases. The exchange reaction efficiency decreased in the following order: CLV⁻ > PAS⁻ > PIP⁻ >> FUS⁻. The hydrophilicity of the ionic drug conjugates was slightly reduced, as indicated by the increased WCA values. The major fraction of particles with sizes ~20 nm was detected in systems with at least 50% TMAMA carrying PAS or PIP. The influence of the drug character and carrier structure was also observed in the kinetic profiles of the release processes driven by the exchange with phosphate anions (0.5–6.4 μg/mL). The obtained polymer-drug ionic conjugates (especially that with PAS) are promising carriers with potential medical applications.

Multiscale Simulations of Clavulanate Inhibition Identify the Reactive Complex in Class A β-Lactamases and Predict the Efficiency of Inhibition

Clavulanate is used as an effective drug in combination with β-lactam antibiotics to treat infections of some antibiotic resistant bacteria. Here, we perform combined quantum mechanics/molecular mechanics simulations of several covalent complexes of clavulanate with class A β-lactamases KPC-2 and TEM-1. Simulations of the deacylation reactions identify the decarboxylated trans-enamine complex as being responsible for inhibition. Further, the obtained free energy barriers discriminate clinically relevant inhibition (TEM-1) from less effective inhibition (KPC-2).

Development and validation of stability-indicating HPLC method for simultaneous determination of meropenem and potassium clavulanate

A stability-indicating LC assay method was developed and validated for a simultaneous determination of meropenem and potassium clavulanate in the presence of degradation products formed during acid-base hydrolysis, oxidation and thermolysis. The isocratic RP-HPLC method was developed with a LiChrospher RP-18 (250 mm x 4.6 mm, 5 microm) column and gradient elution of 12 mmol/L ammonium acetate and acetonitrile. The flow rate of the mobile phase was 1.0 mL/min, the detection wavelength 220 nm and the temperature 303 K. The method was validated with regard to linearity, accuracy, precision, selectivity and robustness, and was applied successfully for the determination of meropenem and potassium clavulanate separately as well as jointly in pharmaceutical formulations.

Separation of clavulanic acid from fermented broth of amino acids by an aqueous two-phase system and ion-exchange adsorption

The clavulanic acid is a substance which inhibits the β-lactamases used with penicillins for therapeutic treatment. After the fermentation, by-products of low molecular weight such as amino acids lysine, histidine, proline and tyrosine are present in the fermented broth. To remove these impurities the techniques of extraction by an aqueous two-phase system of 17% polyethylene glycol molecular weight 600 and 15% potassium phosphate were used for a partial purification. A subsequent ion-exchange adsorption was used for the recuperation of the clavulanic acid of the top phase and purification getting a concentration factor of 2 and purification of 100% in relation to the amino acids lysine, histidine, proline and tyrosine.

Overcoming Resistance to β-Lactamase Inhibitors: Comparing Sulbactam to Novel Inhibitors against Clavulanate Resistant SHV Enzymes with Substitutions at Ambler Position 244

Amino acid changes at Ambler position R244 in class A TEM and SHV beta-lactamases confer resistance to ampicillin/clavulanate, a beta-lactam/beta-lactamase inhibitor combination used to treat serious infections. To gain a deeper understanding of this resistance phenotype, we investigated the activities of sulbactam and two novel penem beta-lactamase inhibitors with sp2 hybridized C3 carboxylates and bicyclic R1 side chains against a library of SHV beta-lactamase variants at the 244 position. Compared to SHV-1 expressed in Escherichia coli, all 19 R244 variants exhibited increased susceptibility to ampicillin/sulbactam, an important difference compared to ampicillin/clavulanate. Kinetic analyses of SHV-1 and three SHV R244 (-S, -Q, and -L) variants revealed the Ki for sulbactam was significantly elevated for the R244 variants, but the partition ratios, kcat/kinact, were markedly reduced (13 000 --> <or=500). A timed inactivation-mass spectrometry analysis of SHV inhibited by sulbactam showed that SHV-1 beta-lactamase was unmodified at 15 min. A parallel experiment with R244S demonstrated 70 and 88 +/- 3 Da fragments of sulbactam covalently attached to the beta-lactamase. We also observed that the Ki values of penems 1 and 2 were increased for R244 variants compared to those for SHV; however, these inhibitors effectively restored ampicillin susceptibility in vitro. Compared to that of sulbactam, the kcat/kinact values of penems for SHV-1 and R244S were low (<or=2), and unfragmented adducts of each penem were covalently attached to SHV-1 and R244S when studied using the timed inactivation-mass spectrometry method. The R244S mutation affects beta-lactamase inactivators differently, but resistance can be overcome by designing penem inhibitors with strategic chemical properties that improve affinity and impair turnover.

Kinetics of amoxicillin and clavulanate degradation alone and in combination in aqueous solution under frozen conditions

Kinetics of the reactions of amoxicillin sodium and potassium clavulanate alone and in combination were investigated in the frozen state at selected pH values of 2.0, 4.6 and 7.0. Extrapolation of the rate constant values to the frozen state from the liquid state data indicated marked acceleration of the rates of amoxicillin and clavulanate degradation for the pH values investigated. The highest acceleration in rate recorded was 15.0-fold for clavulanate and the lowest value was 4.6-fold for amoxicillin at -7.3 degrees C in the hydrochloric acid system. The rate constant values obtained were interpreted in terms of the concentration model [Pincock, R.E., Kiovsky, T.E., 1966. Kinetics of reactions in frozen solution. J. Chem. Educ. 43, 358-360], phase-temperature relationship of the solutes, buffer catalysis, pH change and polymerization reactions. A kinetic model was deduced for the hydrochloric acid system providing adequate explanation of the experimental results. A large stabilizing effect of sodium chloride used for maintaining constant ionic strength (micro=0.5) was evident in this system. The shelf-life of amoxicillin was increased from 2.2 to 58.7h at -7.3 degrees C when sodium chloride was included in the hydrochloric acid system.

A statistical approach using L(25) orthogonal array method to study fermentative production of clavulanic acid by Streptomyces clavuligerus MTCC 1142

Clavulanic acid is a naturally occurring antibiotic produced by Streptomyces clavuligerus. The present work reports on clavulanic acid production by Streptomyces clavuligerus MTCC 1142 using one-factor-at-a-time and L(25) orthogonal array. The one-factor-at-a-time method was adopted to investigate the effect of media components (i.e., carbon source, nitrogen source and inoculum concentration) and environmental factors such as pH for clavulanic acid production. Production of clavulanic acid by Streptomyces clavuligerus was investigated using seven different carbon sources (viz. glucose, sucrose, modified starch, rice-bran oil, soybean oil, palm oil, and glycerol) and six different nitrogen sources (viz. peptone, yeast extract, ammonium chloride, ammonium carbonate, sodium nitrate and potassium nitrate). A maximum yield of 140 microg/mL clavulanic acid was obtained in the medium containing soybean oil as a carbon source and yeast extract as nitrogen source. Subsequently, the concentration of soybean flour, soybean oil, dextrin, yeast extract and K2HPO4 were optimized using L25 orthogonal array method. The final optimized medium produced 500 microg/mL clavulanic acid at the end of 96 h as compared to 140 microg/mL before optimization. Synthesis of precursor molecules as a metabolic driving force is of considerable importance in antibiotic synthesis. Attempts to increase the clavulanic acid synthesis by manipulating the anaplerotic flux on C(3) and C(5) precursors by supplementing the medium with arginine, ornithine, proline, valine, leucine, isoleucine, pyruvic acid and alpha-ketoglutarate were successful. Supplementing the optimized medium with 0.1 M arginine and 0.1 M leucine increased the yield of clavulanic acid further to 1100 microg/mL and 1384 microg/mL respectively.

Sulbactam forms only minimal amounts of irreversible acrylate-enzyme with SHV-1 beta-lactamase

Sulbactam is a mechanism-based inhibitor of beta-lactamase enzymes used in clinical practice. It undergoes a complex series of chemical reactions in the active site that have been studied extensively in the past three decades. However, the actual species that gives rise to inhibition in a clinical setting has not been established. Recent studies by our group, using Raman microscopy and X-ray crystallography, have found that large quantities of enamine-based acyl-enzyme species are present within minutes in single crystals of SHV-1 beta-lactamases which can lead to significant inhibition. The enamines are formed by breakdown of the cyclic beta-lactam structures with further transformations leading to imine formation and subsequent isomerization to cis and/or trans enamines. Another favored form of inhibition arises from attack on the imine by a second nucleophilic amino acid side chain, e.g., from serine 130, to form a cross-linked species in the active site that can degrade to an acrylate-like species irreversibly bound to the enzyme. Thus, the imine is at a branch point on the reaction pathway. Using sulbactam and 6,6-dideuterated sulbactam we follow these alternate paths in WT and E166A SHV-1 beta-lactamase by means of Raman microscopic studies on single enzyme crystals. For the unlabeled sulbactam, the Raman data show the presence of an acrylate-like species, probably 3-serine acrylate, several hours after the reaction is started in the crystal. However, for the 6,6-dideutero analogue the acrylate signature appears on the time scale of minutes. The Raman signatures, principally an intense feature near 1530 cm-1, are assigned based on quantum mechanical calculations on model compounds that mimic acrylate species in the active site. The different time scales observed for acrylate-like product formation are ascribed to different rates of reaction involving the imine intermediate. It is proposed that for the unsubstituted sulbactam the conversion from imine to enamine, which involves breaking a C-H bond, is aided by quantum mechanical tunneling. For the 6,6-dideutero-sulbactam the same step involves breaking a C-D bond, which has little or no assistance from tunneling. Consequently the conversion to enamines is slower, and a higher population of imine results, presenting the opportunity for the competing reaction with the second nucleophile, serine 130 being the prime candidate. The hydrolysis of the resulting cross-linked intermediate leads to the observed rapid buildup of the acrylate product in the Raman spectra from the dideutero analogue. The protocol used here, essentially running the reactions with the two forms of sulbactam in parallel, provides an element of control and enables us to conclude that, for the unsubstituted sulbactam, the formation of the cross-linked intermediate and the final irreversible acrylate product is not a significant route to inhibition of SHV-1.

Quantitative analysis of clavulanic acid in porcine tissues by liquid chromatography combined with electrospray ionization tandem mass spectrometry

The purpose of this study was to develop and validate a method for the determination of clavulanic acid (CLAV) residues in edible tissues of swine by liquid chromatography-electrospray ionisation-tandem mass spectrometry (LC-ESI-MS/MS). After a simple extraction of CLAV using an aqueous phosphate buffer solution of pH 6.0, an ultrafiltration step was performed for protein removal. Chromatography of CLAV and the internal standard tazobactam (TAZO) was achieved on a reversed-phase PLRP-S polymeric column (150 mm x 2.1 mm i.d., 100 A) using a mixture of 0.05 (v/v)% formic acid in water and acetonitrile. The mass spectrometer was operated in the MS/MS selected reaction monitoring (SRM) mode. The method was validated for the analysis of porcine muscle, skin plus fat, liver and kidney, according to the requirements defined by the European Community. Calibration curves were prepared for all tissues and good linearity was achieved over the concentration ranges tested (correlation coefficient > or = 0.99 and goodness-of-fit coefficient < or = 10%). Limits of quantification of 50 ng g(-1) were obtained for the analysis of CLAV in the various tissues which corresponds in all cases to at least half the maximum residue limits (MRLs). Limits of detection ranged between 8.0 and 15.14 ng g(-1). The within-day, between-day precisions and trueness fell within the ranges specified in the EMEA/CVMP/573-00/FINAL document. Biological samples from pigs that received an oral or intravenous bolus of a commercial amoxicillin/clavulanic acid formulation were analyzed using the described method.

Optimization of nutritional requirements and feeding strategies for clavulanic acid production by Streptomyces clavuligerus

The present work reports the nutritional requirements and environmental conditions for submerged culture of Streptomyces clavuligerus for clavulanic acid production using orthogonal matrix method (Taguchi L(16) design) and also fed-batch fermentation for clavulanic acid production by feeding glycerol, arginine and threonoine to the fermentation medium intermittently. Clavulanic acid production was increased by 18% with the span of feeding glycerol and reached a maximum at 1.30mg/ml with 120h glycerol feeding as compared to 1.10mg/ml in the control. The production also increased with the span of feeding amino acids and reached a maximum of 1.31 and 1.86mg/ml with feeding arginine and threonine, respectively in 120h. There was an overall increase of 18% and 9% in clavulanic acid production with arginine and threonine feeding as compared to the respective controls (1.10 and 1.70mg/ml, respectively).

Raman crystallographic studies of the intermediates formed by Ser130Gly SHV, a beta-lactamase that confers resistance to clinical inhibitors

Antibiotic resistance to beta-lactam compounds in Gram-negative bacteria such as Escherichia coli and Klebsiella pneumoniae is often mediated by beta-lactamase enzymes like TEM and SHV. Previously, a limited number of inhibitors have shown efficacy in combating such bacterial drug resistance. However, many Gram-negative pathogens have evolved inhibitor resistant forms of these hydrolytic enzymes. A single point mutation of the active site residue Ser130 to a Gly in either TEM or SHV results in resistance to amoxicillin and clavulanic acid, an important clinical beta-lactam-beta-lactamase inhibitor combination antibiotic. Previous structural and modeling studies of the S130G mutants of TEM and SHV have shown differences in how these two distinct but closely related enzymes compensate for the loss of the Ser130 residue. In the case of S130G SHV, a structure of tazobactam in the active site has suggested that the inhibitor preferentially assumes a cis-enamine intermediate form when the Ser130 hydroxyl is absent. Raman crystallographic studies of S130G SHV inhibited with tazobactam, sulbactam, clavulanic acid, and 2'-glutaroxy penem sulfone (SA2-13) were performed with the aim of identifying the type and amount of intermediate formed with each drug to understand the role of the S130G mutation in formation of the important enamine intermediates. It is demonstrated that with the exception of sulbactam, each compound forms observable trans-enamine intermediates. For S130G reacted with tazobactam, identical steady state levels of enamine are achieved when compared to those of wild-type (WT) or even deacylation deficient forms of the enzyme. With clavulanic acid, slightly smaller amounts of enamine are observed within the first 30 min of the reaction but are not significantly different than those for tazobactam. Thus, the resistance mutation does not substantially affect the amount of trans-enamine formed with clavulanic acid during the critical early time period of inhibition. This finding has important implications in the design of beta-lactamase inhibitors for drug resistant variants like S130G SHV.

Mechanism for Cyclization Reaction by Clavaminic Acid Synthase. Insights from Modeling Studies

The mechanism of the oxidative cyclization reaction catalyzed by clavaminic acid synthase (CAS) was studied in silico. First, a classical molecular dynamics (MD) simulation was performed to obtain a realistic structure of the CAS-Fe(IV)=O-succinate-substrate complex; then potential of mean force (PMF) was calculated to assess the feasibility of the beta-lactam ring, more specifically its C4' corner, approaching the oxo atom. Based on the MD structure, a relatively large model of the active site region was selected and used in the B3LYP investigation of the reaction mechanism. The computational results suggest that once the oxoferryl species is formed, the oxidative cyclization catalyzed by CAS most likely involves either a mechanism involving C4'(S)-H bond cleavage of the monocyclic beta-lactam ring, or a biosynthetically unprecedented mechanism comprising (1) oxidation of the hydroxyl group of PCA to an O-radical, (2) retro-aldol-like decomposition of the O-radical to an aldehyde and a C-centered radical, which is stabilized by the captodative effect, (3) abstraction of a hydrogen atom from the C4'(S) position of the C-centered radical by the Fe(III)-OH species yielding an azomethine ylide, and (4) 1,3-dipolar cycloaddition to the ylide with aldehyde acting as a dipolarophile. Precedent for the new proposed mechanism comes from the reported synthesis of oxapenams via 1,3-dipolar cycloaddition reactions of aldehydes and ketones.

Structure and Raman Spectrum of Clavulanic Acid in Aqueous Solution

The calculation of the vibrational Raman spectrum of enzyme-bound beta-lactamase inhibitors may be of help to understand the mechanisms responsible for bacterial drug resistance. Here, we present a study of the solvation structure and the vibrational properties of clavulanate, an important beta-lactamase inhibitor, in aqueous solution as obtained from full quantum and hybrid empirical/quantum molecular dynamics simulations at ambient conditions. The analysis of the vibrational density of states indicates that hybrid empirical/quantum mechanical simulations are able to properly describe the vibrational levels of clavulanate in solution. In addition, we propose a computationally efficient protocol to calculate the vibrational Raman effect for large solute molecules in water, which is able to faithfully reproduce the experimentally recorded clavulanate Raman spectrum and discloses the possibility to employ hybrid simulations to assign the experimental Raman spectra of inhibitors bound to beta-lactamases.

ORF17 from the clavulanic acid biosynthesis gene cluster catalyzes the ATP-dependent formation of N-glycyl-clavaminic acid

(3R,5R)-Clavulanic acid, a clinically used inhibitor of serine beta-lactamases, is produced by fermentation of Streptomyces clavuligerus. The early steps in clavulanic acid biosynthesis leading to the bicyclic beta-lactam intermediate (3S,5S)-clavaminic acid have been defined. However, the mechanism by which (3S,5S)-clavaminic acid is converted to the penultimate intermediate (3R,5R)-clavaldehyde is unclear. Disruption of orf15 or orf16, of the clavulanic acid biosynthesis gene cluster, blocks clavulanic acid production and leads to the accumulation of N-acetyl-glycyl-clavaminic acid and N-glycyl-clavaminic acid, suggesting that these compounds are intermediates in the pathway. Two alternative start codons have been proposed for orf17 to encode for two possible polypeptides, one of which has 92 N-terminal residues less then the other. The shorter version of orf17 was successfully expressed in Escherichia coli and purified as a monomeric protein. Sequence analyses predicting the ORF17 protein to be a member of the ATP-grasp fold superfamily were supported by soft ionization mass spectrometric analyses that demonstrated binding of ATP to the ORF17 protein. Semisynthetic clavaminic acid, prepared by in vitro reconstitution of the biosynthetic pathway from the synthetically accessible intermediate proclavaminic acid, was shown by mass spectrometric analyses to be converted to N-glycyl-clavaminic acid in the presence of ORF17, ATP, and glycine. Under the same conditions N-acetyl-glycine and clavaminic acid were not converted to N-acetyl-glycyl-clavaminic acid. The specificity of ORF17 as an N-glycyl-clavaminic acid synthetase, together with the reported accumulation of N-glycyl-clavaminic acid in orf15 and orf16 disruption mutants, suggested that N-glycyl-clavaminic acid is an intermediate in clavulanic acid biosynthesis.

Information Content in Organic Molecules: Aggregation States and Solvent Effects

The information content of organic molecules has been the subject of a series of papers from this lab. The investigation continues as aggregation states and some of their attendant solvent effects are examined. An organic molecule operates as an information source not in a vacuum but rather in conjunction with one or more solvent compounds. Accordingly, solvents (ethanol, acetone, etc.) furnish both a source and a channel that modify molecular information. In this paper, Brownian techniques are developed further so as to quantify molecular information with aggregation states taken into account. Several applications follow concerning organic acid ionization in solution, tautomerization reactions, and molecular activity at biological receptor sites. The goal is to advance Brownian processing as a means of probing molecular information and its communication. To this end, practical examples are offered relating structure and function along informatic lines.

Combined chemical and biological oxidation of penicillin formulation effluent

Antibiotic formulation effluent is well known for its important contribution to environmental pollution due to its fluctuating and recalcitrant nature. In the present study, the chemical treatability of penicillin formulation effluent (average filtered COD(o)=830 mg/l; average soluble COD(o)=615 mg/l; pH(o)=6.9) bearing the active substances penicillin Amoxicillin Trihydrate (C(16)H(19)N(3)O(5)S.3H(2)O) and the beta-lactamase inhibitor Potassium Clavulanate (C(8)H(8)KNO(5)) has been investigated. For this purpose, the penicillin formulation effluent was subjected to ozonation (applied ozone dose=2500 mg/(lxh)) at varying pH (2.5-12.0) and O(3)+H(2)O(2) (perozonation) at different initial H(2)O(2) concentrations (=2-40 mM) and pH 10.5. According to the experimental results, the overall Chemical Oxygen Demand (COD) removal efficiency varied between 10 and 56% for ozonation and 30% (no H(2)O(2)) and 83% (20 mM H(2)O(2)) for the O(3)+H(2)O(2) process. The addition of H(2)O(2) improved the COD removal rates considerably even at the lowest studied H(2)O(2) concentration. An optimum H(2)O(2) concentration of 20 mM existed at which the highest COD removal efficiency and abatement kinetics were obtained. The ozone absorption rate ranged between 53% (ozonation) and 68% (perozonation). An ozone input of 800 mg/l in 20 min was sufficient to achieve the highest BOD(5)/COD (biodegradability) ratio (=0.45) and BOD(5) value (109 mg/l) for the pre-treated penicillin formulation effluent. After the establishment of optimum ozonation and perozonation conditions, mixtures of synthetic domestic wastewater+raw, ozonated and perozonated penicillin formulation effluent were subjected to biological activated sludge treatment at a food-to-microorganisms (F/M) ratio of 0.23 mg COD/(mg MLSSxd), using a consortium of acclimated microorganisms. COD removal efficiencies of the activated sludge process were 71, 81 and 72% for pharmaceutical wastewater containing synthetic domestic wastewater mixed with either raw, ozonated or perozonated formulation effluent, respectively. The ultimate COD value obtained after 24-h biotreatment of the synthetic domestic wastewater+pre-ozonated formulation effluent mixture was around 100 mg/l instead of 180 mg/l which was the final COD obtained for the wastewater mixture containing raw formulation effluent, indicating that pre-ozonation at least partially removed the non-biodegradable COD fraction of the formulation effluent.

Crystal Structure and Mechanistic Implications of N2-(2-Carboxyethyl)arginine Synthase, the First Enzyme in the Clavulanic Acid Biosynthesis Pathway

The initial step in the biosynthesis of the clinically important beta-lactamase inhibitor clavulanic acid involves condensation of two primary metabolites, D-glyceraldehyde 3-phosphate and L-arginine, to give N2-(2-carboxyethyl)arginine, a beta-amino acid. This unusual N-C bond forming reaction is catalyzed by the thiamin diphosphate (ThP2)-dependent enzyme N2-(2-carboxyethyl)arginine synthase. Here we report the crystal structure of N2-(2-carboxyethyl)arginine synthase, complexed with ThP2 and Mg2+, to 2.35-A resolution. The structure was solved in two space groups, P2(1)2(1)2(1) and P2(1)2(1)2. In both, the enzyme is observed in a tetrameric form, composed of a dimer of two more tightly associated dimers, consistent with both mass spectrometric and gel filtration chromatography studies. Both ThP2 and Mg2+ cofactors are present at the active site, with ThP2 in a "V" conformation as in related enzymes. A sulfate anion is observed in the active site of the enzyme in a location proposed as a binding site for the phosphate group of the d-glyceraldehyde 3-phosphate substrate. The mechanistic implications of the active site arrangement are discussed, including the potential role of the aminopyrimidine ring of the ThP2. The structure will form a basis for future mechanistic and structural studies, as well as engineering aimed at production of alternative beta-amino acids.

Following the Reactions of Mechanism-Based Inhibitors with β-Lactamase by Raman Crystallography

The reactions between three clinically relevant inhibitors, tazobactam, sulbactam, and clavulanic acid, and SHV beta-lactamase (EC 3.5.2.6) have been followed in single crystals using a Raman microscope. The data are far superior to those obtained for the enzyme in aqueous solution and allow us to identify species on the reaction pathway and to measure the rates of the accumulation and decay of these species. A key intermediate on the reaction pathway is an acyl enzyme formed between Ser70 and the lactam ring's C=O group. By using the E166A deacylation deficient variant of the enzyme, we were able to focus on the process of acyl enzyme formation. The Raman data show that all three inhibitors form an enamine-type acyl enzyme reaching maximal populations at 10, 22, and 29 min for sulbactam, clavulanic acid, and tazobactam, respectively. The enamine intermediate exhibits a characteristic and relatively intense band near 1595 cm(-1) due to a stretching motion of the O=C-C=C-NH moiety that shifts to lower frequency upon NH <--> ND exchange. This feature was used to follow the kinetics of enamine buildup and decay in the crystal. Quantum mechanical calculations support the assignment of the 1595 cm(-1) band, as well as several other bands, to a trans-enamine species. The Raman data also demonstrate that the lactam ring opens prior to enamine formation since the lactam ring carbonyl (C=O) peak disappears prior to the appearance of the enamine 1595 cm(-1) band. Tazobactam appears to form approximately twice as much enamine intermediate as sulbactam and clavulanic acid, which correlates with its superior performance in the clinic, a finding that may bear on future drug design.

Industrial production of beta-lactam antibiotics

The industrial production of beta-lactam antibiotics by fermentation over the past 50 years is one of the outstanding examples of biotechnology. Today, the beta-lactam antibiotics, particularly penicillins and cephalosporins, represent the world's major biotechnology products with worldwide dosage form sales of approximately 15 billion US dollars or approximately 65% of the total world market for antibiotics. Over the past five decades, major improvements in the productivity of the producer organisms, Penicillium chrysogenum and Acremonium chrysogenum (syn. Cephalosporium acremonium) and improved fermentation technology have culminated in enhanced productivity and substantial cost reduction. Major fermentation producers are now estimated to record harvest titers of 40-50 g/l for penicillin and 20-25 g/l for cephalosporin C. Recovery yields for penicillin G or penicillin V are now >90%. Chemical and enzymatic hydrolysis process technology for 6-aminopenicillanic acid or 7-aminocephalosporanic acid is also highly efficient (approximately 80-90%) with new enzyme technology leading to major cost reductions over the past decade. Europe remains the dominant manufacturing area for both penicillins and cephalosporins. However, due to ever increasing labor, energy and raw material costs, more bulk manufacturing is moving to the Far East, with China, Korea and India becoming major production countries with dosage form filling becoming more dominant in Puerto Rico and in Ireland.

Application of MEKC for determination of ticarcillin and clavulanic acid in Timentin intravenous preparation

A micellar electrokinetic chromatography method for simultaneous assay of ticarcillin and clavulanic acid in Timentin i.v. injection preparation was developed. This method ensures excellent separation of both components of Timentin preparation. The validation of the method was performed, and specificity, reproducibility, precision and accuracy were confirmed. The detection and quantitative limits for Timentin were established in the concentrations 0.04 and 0.08 mg/ml, respectively. The elaborated technique was compared with two methods routinely used-UV and high performance liquid chromatography (HPLC). The obtained results and their statistical analysis proved the same precision of all methods, however, no significant differences were observed between CE and HPLC.

Identical pattern of highly variable absorption of clavulanic acid from four different oral formulations of co-amoxiclav in healthy subjects

The aims of this investigation were to calculate the pharmacokinetic parameters of amoxicillin and clavulanic acid, and to identify parameters that may affect their observed differences in absorption. Data were obtained from plasma concentration-time curves from four different open, randomized, two-treatment, two-period, two-sequence, crossover Phase I bioequivalence studies, with the following co-amoxiclav formulations: tablets 250/125, 500/125 and 875/125 mg, or 10 mL of an oral suspension 250/62.5 mg per 5 mL. Data from 144 subjects and 288 drug administrations were available for evaluation. After a 125 mg clavulanic acid dose (administered as potassium clavulanate) for all four different formulations, the clavulanic acid AUC(t) data ranged from 1.5 to 8 mg.h/L, varying by a factor of 5. The absorption of clavulanic acid was not related to the absorption of amoxicillin, or demographic factors, and we were unable to identify the reasons for the large variability in the absorption of clavulanic acid. We conclude that the absorption of clavulanic acid, after oral administration, is highly variable and may vary over a five-fold range between patients.

Factors governing intrinsic chemical reactivity differences between clavulanic and penicillanic acids

To help elucidate why penicillin-G is inactivated by certain bacterial beta-lactamase enzymes, whereas clavulanic acid (Clav, which is similar to penicillin-G except at positions 1, 2, and 6) inhibits beta-lactamase, the intrinsic chemical reactivities of these two antibiotics were assessed in this work. Ab initio and continuum dielectric methods were used to map out the gas-phase and solution-phase free-energy profiles for the alkaline hydrolyses of Clav and penicillanic acid (Peni, which is similar to penicillin-G except at position 6) as well as of a fictitious hybrid compound, Peni-db, which is similar to Clav and Peni except at positions 1 and 2, respectively. Furthermore, the ring strain energies of various lactam rings and the five-membered rings of Peni and Clav as well as their respective rate-limiting transition states were computed to assess the contribution of four- and five-membered ring strains to the antibiotic's activity. The predicted product distribution, rate-limiting step, and relative reaction rates for the alkaline hydrolysis of Peni and Clav are in accord with the experimental findings. The rate-limiting step in the alkaline hydrolysis of Peni, Clav, or Peni-db is the approach of the negatively charged hydroxide ion toward the anionic reactant to form a tetrahedral intermediate. The alkaline hydrolysis of Clav generates more stable products than that of Peni mainly because the O1 atom and the hydroxyethylidene group in Clav facilitate the opening of the five-membered ring; furthermore, the O1 atom can abstract a proton easier than the less polar S1 in Peni. Clav undergoes basic hydrolysis faster than Peni mainly because its hydroxyethylidene group leads to an increase in the positive charge on the carbonyl C7 atom, therefore enhancing favorable electrostatic interactions with the incoming hydroxide anion. To a lesser extent, the oxygen at position 1 in Clav also contributes to the rate acceleration because of the greater solvent stabilization of the oxygen-containing transition state as compared to the respective ground state. The inherent strain of the four-membered beta-lactam ring or five-membered ring does not enhance the alkaline hydrolyses of beta-lactam molecules such as Peni or Clav, consistent with the observation that the rate-limiting step does not involve a breakdown of the four-membered beta-lactam ring or five-membered thiazolidine/oxazolidine rings.

New reactions in clavulanic acid biosynthesis

Clavulanic acid is only a modestly effective antibiotic against bacterial infections in humans, but a potent inhibitor/inactivator of beta-lactamase enzymes that confer bacterial resistance. The biosynthetic pathway to clavulanic acid is considerably more complex than that to the structurally related penicillins and cephalosporins and has revealed several interesting reactions.

Removal of the fermentation by-product succinylL-tyrosine from the ?-lactamase inhibitor clavulanic acid using a molecularly imprinted polymer

Clavulanic acid is a beta-lactamase inhibitor used in therapeutic combinations with the penicillin-type antibiotics. During the fermentation leading to clavulanic acid, a succinyl L-tyrosine by-product is unavoidably formed. Occasionally, the amount of this by-product is found to be as high as 2% of the product even after standard purification operations. To further remove this impurity, we prepared a highly specific adsorbent for succinyl L-tyrosine with the molecular imprinting technique. This was performed by simultaneously using vinylbenzyl trimethylammonium chloride and methacrylic acid as the functional monomers. The imprinted polymer selectively bound succinyl L-tyrosine, and could be successfully used to remove this impurity at concentrations of less than 2% in the presence of clavulanic acid.

5-Dethia-5-oxacephams: toward correlation of absolute configuration and chiroptical properties

The relationship between chiroptical properties of differently substituted 5-dethia-5-oxacephams and their respective molecular structures was investigated. The amide chromophore of the beta-lactam unit in these compounds was found to be nonplanar with a shallow pyramidal configuration at the nitrogen atom. Due to the nonplanarity, the beta-lactam system becomes inherently dissymmetric, which is supported by a high magnitude of the n --> pi* CD band. It was also found that the helicity of the lactam moiety in investigated oxacephams is controlled by the absolute configuration at the C(6) carbon atom. On this basis, a helicity rule correlating a positive (negative) sign of the n right arrow pi Cotton effect with a negative (positive) O [double bond] C [bond] N [bond] C(6) torsional angle for policyclic beta-lactam derivatives possessing a nonplanar amide chromophore was formulated.

Structure of beta-lactam synthetase reveals how to synthesize antibiotics instead of asparagine

The enzyme beta-lactam synthetase (beta-LS) catalyzes the formation of the beta-lactam ring in clavulanic acid, a clinically important beta-lactamase inhibitor. Whereas the penicillin beta-lactam ring is generated by isopenicillin N synthase (IPNS) in the presence of ferrous ion and dioxygen, beta-LS uses ATP and Mg2+ as cofactors. According to sequence alignments, beta-LS is homologous to class B asparagine synthetases (AS-Bs), ATP/Mg2+-dependent enzymes that convert aspartic acid to asparagine. Here we report the first crystal structure of a beta-LS. The 1.95 A resolution structure of Streptomyces clavuligerus beta-LS provides a fully resolved view of the active site in which substrate, closely related ATP analog alpha,beta-methyleneadenosine 5'-triphosphate (AMP-CPP) and a single Mg2+ ion are present. A high degree of substrate preorganization is observed. Comparison to Escherichia coli AS-B reveals the evolutionary changes that have taken place in beta-LS that impede interdomain reaction, which is essential in AS-B, and that accommodate beta-lactam formation. The structural data provide the opportunity to alter the synthetic potential of beta-LS, perhaps leading to the creation of new beta-lactamase inhibitors and beta-lactam antibiotics.

Evaluation of inhibition of the carbenicillin-hydrolyzing beta-lactamase PSE-4 by the clinically used mechanism-based inhibitors

Characterization of the biochemical steps in the inactivation chemistry of clavulanic acid, sulbactam and tazobactam with the carbenicillin-hydrolyzing beta-lactamase PSE-4 from Pseudomonas aeruginosa is described. Although tazobactam showed the highest affinity to the enzyme, all three inactivators were excellent inhibitors for this enzyme. Transient inhibition was observed for the three inactivators before the onset of irreversible inactivation of the enzyme. Partition ratios (k(cat)/k(inact)) of 11, 41 and 131 were obtained with clavulanic acid, tazobactam and sulbactam, respectively. Furthermore, these values were found to be 14-fold, 3-fold and 80-fold lower, respectively, than the values obtained for the clinically important TEM-1 beta-lactamase. The kinetic findings were put in perspective by determining the computational models for the pre-acylation complexes and the immediate acyl-enzyme intermediates for all three inactivators. A discussion of the pertinent structural factors is presented, with PSE-4 showing subtle differences in interactions with the three inhibitors compared to the TEM-1 enzyme.

The claR gene of Streptomyces clavuligerus, encoding a LysR-type regulatory protein controlling clavulanic acid biosynthesis, is linked to the clavulanate-9-aldehyde reductase (car) gene

Two genes, claR and car, encoding proteins involved in clavulanic acid biosynthesis, have been found in a 2.8-kb BglII-EcoRI DNA fragment of Streptomyces clavuligerus adjacent to the region containing the cephamycin and clavulanic acid biosynthesis gene cluster. claR encoded a protein of 431 amino acids (deduced Mr 47080), that showed a significant degree of homology with several transcriptional activators of the LysR family. The ClaR protein contained two helix-turn-helix (HTH) motifs in the amino and carboxyl terminal regions. The second gene, car, encoded a protein of 247 amino acids (Mr 26629) that showed a strong similarity to oxydoreductases of the SDR family. Twelve amino acids of the amino-terminal region were identical to those previously obtained by Edman degradation of the purified clavulanic-9-aldehyde reductase of S. clavuligerus. Amplification of the claR gene in multicopy plasmids resulted in a threefold increase in clavulanic acid production and in a five- to sixfold increase of alanylclavam biosynthesis, whereas cephamycin production was significantly reduced both in defined and in complex media. By contrast, amplification of the car gene had no significant effect on clavulanic acid and alanylclavam or cephamycin production. Both claR and car are expressed as monocistronic transcripts; the level of transcript declined rapidly after 48h in complex media, but low sustained levels of both transcripts were observed in defined GSPG medium until 96h. claR and car were not significantly expressed in mutants disrupted in the ccaR gene, a regulatory gene that controls positively clavulanic acid and cephamycin biosynthesis. These results indicate that clavulanic acid and cephamycin biosynthesis in S. clavuligerus is controlled by a cascade of regulatory proteins that include CcaR and ClaR.

Clinical inhibitor-resistant mutants of the beta-lactamase TEM-1 at amino-acid position 69. Kinetic analysis and molecular modelling

The kinetic parameters of three IRT (Inhibitor-Resistant-TEM-derived-) beta-lactamases (IRT-5, IRT-6 and IRT-I69) were determined for substrates and the beta-lactamase inhibitors: clavulanic acid, sulbactam and tazobactam, and compared with those of TEM-1 beta-lactamase. The catalytic behaviour of the beta-lactamases towards substrates and inhibitors was correlated with the properties of the amino acid at position ABL69. The three IRT beta-lactamases contain at that position a residue Ile, Leu and Val, amino acids whose side-chain are branched. Molecular modelling shows that the methyl groups of Ile-69 (C gamma 2) and Val-69 (C gamma 1) produced steric constraints with the side chain of Asn-170 as well as the main chain nitrogen of Ser-70, a residue contributing to the oxyanion hole. We suggest that hydrophobicity could be the main factor responsible for the kinetic properties of Met69Leu (IRT-5), as no steric effects could be detected by molecular modelling. Hydrophobicity and steric constraints are combined in Met69Ile and Met69Val, IRT-I69 and IRT-6, respectively.