The isolation and kinetics of penicillin amidase from Escherichia coli

Selective adsorption of poly-His tagged glutaryl acylase on tailor-made metal chelate supports

A poly-His tag was fused in the glutaryl acylase (GA) from Acinetobacter sp. strain YS114 cloned in E. coli yielding a fully active enzyme. Biochemical analyses showed that the tag did not alter the maturation of the chimeric GA (poly-His GA) that undergoes a complex post-translational processing from an inactive monomeric precursor to the active heterodimeric enzyme. This enzyme has been used as a model to develop a novel and very simple procedure for one-step purification of poly-His proteins via immobilized metal-ion affinity chromatography on tailor-made supports. It was intended to improve the selectivity of adsorption of the target protein on tailor-made chelate supports instead of performing a selective desorption. The rate and extent of the adsorption of proteins from a crude extract from E. coli and of pure poly-His tagged GA on different metal chelate supports was studied. Up to 90% of proteins from E. coli were adsorbed on commercial chelate supports having a high density of ligands attached to the support through long spacer arms, while this adsorption becomes almost negligible when using low ligand densities, short spacer arms and Zn2+ or Co2+ as cations. On the contrary, poly-His GA adsorbs strongly enough on all supports. A strong affinity interaction between the poly-His tail and a single chelate moiety seems to be the responsible for the adsorption of poly-His GA. By contrast, multipoint weak interactions involving a number of chelate moieties seem to be mainly responsible for adsorption of natural proteins. By using tailor-made affinity supports, a very simple procedure for one-step purification of GA with minimal adsorption of host proteins could be performed. Up to 20 mg of GA were adsorbed on each ml of chelate support while most of accompanying proteins were hardly adsorbed on such supports. Following few washing steps, the target enzyme was finally recovered (80% yield) by elution with 50 mM imidazole with a very high increment of specific activity (up to a 120 purification factor).

Manipulation of carbon assimilation with respect to expression of the pac gene for improving production of penicillin acylase in Escherichia coli

A strategy of genetically manipulating carbon assimilation with respect to expression of the pac gene was employed for overproduction of recombinant penicillin acylase (PAC). Two expression plasmids of pCLL2902 and pCLL3201, which contain the pac coding region but differ in the pac regulatory region, were constructed for the production experiments. Expression of the pac gene was subjected to phenyl acetic acid (PAA-) induction and glucose catabolite repression for pCLL3201, whereas it was subjected to neither of the two transcriptional regulations for pCLL2902. The specific PAC activity for strains harboring pCLL2902 was significantly higher than that for strains harboring pCLL3201 due to an improved transcription efficiency. In addition, no inclusion bodies were observed upon production of PAC using the current expression systems. The results suggest that using the native pac promoter instead of a strong promoter such as tac for regulation is a feasible approach for production of PAC. The impact of the current expression systems is also significant from a process viewpoint since, using strains harboring pCLL2902, not only could glucose replace PAA as a carbon source of Escherichia coli cultures for production of PAC but also the volumetric PAC activity was highly improved.

Purification and stability of glutaryl-7-ACA acylase from Pseudomonas sp

The enzyme glutaryl-7-ACA acylase from Pseudomonas sp. NCIMB 40474, produced by a recombinant Escherichia coli host, was purified to homogeneity. The enzyme is a tetramer composed of two couples of asymmetric dimers, each of them constituted of two subunits of mol wt 18 and 52 kDa, respectively. It was found that glutaric acid, one of the products of the substrate hydrolysis, is an effective acylase inhibitor. Between pH 6.0 and pH 10.0, the enzymatic activity is almost constant, but below pH 6.0 it progressively declines. The acylase activity decreased sharply as a function of guanidine HCl concentration. The loss is significant even at concentrations of denaturant lower than those causing unfolding, as suggested by UV spectroscopy and fluorescence emission studies. In these conditions (low denaturant concentration and low pH) the inactivation of the enzyme is caused by the tetramer dissociation into dimers. The lability of the quaternary structure of the enzyme is a key feature that must be taken into account for the improvement of the catalyst stability.

Molecular cloning and analysis of the gene encoding the thermostable penicillin G acylase from Alcaligenes faecalis

Alcaligenes faecalis penicillin G acylase is more stable than the Escherichia coli enzyme. The activity of the A. faecalis enzyme was not affected by incubation at 50 degrees C for 20 min, whereas more than 50% of the E. coli enzyme was irreversibly inactivated by the same treatment. To study the molecular basis of this higher stability, the A. faecalis enzyme was isolated and its gene was cloned and sequenced. The gene encodes a polypeptide that is characteristic of periplasmic penicillin G acylase (signal peptide-alpha subunit-spacer-beta subunit). Purification, N-terminal amino acid analysis, and molecular mass determination of the penicillin G acylase showed that the alpha and beta subunits have molecular masses of 23.0 and 62.7 kDa, respectively. The length of the spacer is 37 amino acids. Amino acid sequence alignment demonstrated significant homology with the penicillin G acylase from E. coli A unique feature of the A. faecalis enzyme is the presence of two cysteines that form a disulfide bridge. The stability of the A. faecalis penicillin G acylase, but not that of the E. coli enzyme, which has no cysteines, was decreased by a reductant. Thus, the improved thermostability is attributed to the presence of the disulfide bridge.

Immobilization of whole-cell penicillin G acylase by entrapping within polymethacrylamide beads

Escherichia coli ATCC 11105 containing the periplasmic penicillin G acylase was entrapped within a copolymer of methacrylamide and N,N'-methylenebisacrylamide. A solution of monomer that was made up from methacrylamide and N,N'-methylenebisacrylamide dissolved in buffer was mixed with lyophilized cells and ammonium persulfate. This suspension was then pumped drop by drop into in soybean oil supplemented with 0.06% (v/v) 3-(dimethylamino)-propionitril. During submerging in the oil phase, the droplets were hardened and induced to polymerize within the droplets. Particles with a volume ranging from 0.013-0.017 mL per bead containing a biomass concentration up to 38.0 g/L were prepared. The optimal condition for the deacylation of penicillin G to 6-aminopencillanic acid (6-APA) catalyzed by the immobilized whole-cell penicillin G acylase was found to be 45 degrees C and pH 8.0. Product inhibition of this enzyme by 6-APA could be eliminated by controlling pH value at 8 during the course of penicillin G hydrolysis using a pH-stat. Conversion determined by the pH-stat method were 0.3% higher than that by p-dimethylaminobenzaldehyde method. Cell concentration in the matrix was found to be an important factor influencing the maximum velocity and the specific activity retained in the matrix. A kinetic model, in which the mass transfer resistances as a result of external film mass transfer and pore diffusion were assumed to be negligible, could properly describe the hydrolysis of penicillin G by the cells entrapped within the polymethacylamide beads.

The inhibitory mechanisms of glucose and carbon dioxide on the biosyntheses of penicillins and cephalosporins

The inhibitory mechanism of glucose and CO2 on the biosyntheses of penicillins and cephalosporins is discussed in the present paper. 6-aminopenicillanic acid (6-APA) is considered to be an intermediate product, and the reaction between 6-APA and glucose may play an important role in the yield and rate of biosyntheses of beta-lactam antibiotics. According to this hypothesis the experimental phenomena taking place in biosynthesis of penicillin and cephalosporin, such as the inhibition by glucose and carbon dioxide and the reduction of the yield, can be satisfactorily explained. The stability of 6-aminopenicillanic acid (6-APA) in bicarbonate solution, the reaction of 6-APA with sugars, the determination of the concentration of the 6-APA-sugar compound and the effect of these reactions on the biosynthesis of penicillin G are investigated to present evidences for this hypothesis.

Rapid burst kinetics in the hydrolysis of 4-nitrophenyl acetate by penicillin G acylase from Kluyvera citrophila. Effects of mutation F360V on rate constants for acylation and de-acylation

The kinetics of release of 4-nitrophenol were followed by stopped-flow spectrophotometry with two 4-nitrophenyl ester substrates of penicillin G acylase from Kluyvera citrophila. With the ester of acetic acid, but not of propionic acid, there was a pre-steady-state exponential phase, the kinetics of which were inhibited by phenylacetic acid (a product of hydrolysis of specific substrates) to the extent predicted from Ki values. This was interpreted as deriving from rapid formation (73 mM-1.s-1) and slow hydrolysis (0.76 s-1) of an acetyl derivative of the side chain of the catalytic-centre residue Ser-290. With the mutant F360V, which differs from the wild-type enzyme in its ability to hydrolyse adipyl-L-leucine and has a kcat for 4-nitrophenyl acetate one-twentieth that of the wild-type enzyme, the corresponding values for the rates of formation and hydrolysis of the acetyl-enzyme were 11.1 mM-1.s-1 and 0.051 s-1 respectively. The ratio of these rate constants was three times that for the wild-type enzyme, suggesting that the mutant is less impaired in the rate of formation of an acetyl-enzyme than in its subsequent hydrolysis.

Screening and characterization of microorganisms with glutaryl-7ADCA acylase activity

A screening of microorganisms producing glutaryl-7ADCA acylase, an enzyme able to hydrolyse glutaric acid selectively from glutaryl-3-deacetoxy-7-aminocephalosporanic acid (glutaryl-7ADCA), has been carried out in soil samples. Five microorganisms expressing acylase activity were isolated and classified as Bacillus cereus, Achromobacter xylosooxidans, Bacillus sp., Pseudomonas sp. and Pseudomonas paucimobilis. The screening was carried out by preparing enrichment cultures containing glutaryl-7-ADCA or cephalosporin C as the selective carbon source. Four model compounds (adipoyl-, glutamyl- and glutaryl-p-nitroanilide and glutarylcoumarin), mimicking the glutaryl-7ADCA beta-lactam moiety, were synthesized as substrates suitable for the rapid screening of the microorganisms (2500) isolated from the enrichment cultures. A total of 300 strains were active on the model substrates and only 5 displayed acylase activity on glutaryl-7ADCA. The fermentation parameters, such as pH and inducer concentration, for the optimal acylase expression and acylase specificity towards the model substrates were different for each strain.

Changing the substrate specificity of penicillin G acylase from Kluyvera citrophila through selective pressure

Escherichia coli (muT, mutD, Leu-) cells transformed with plasmid pYKD59 harbouring the pac gene encoding penicillin acylase (PA) from Kluyvera citrophila ATCC 21285 were exposed to environmental conditions that made expression of this enzyme essential for growth. Under these conditions, spontaneous mutants were isolated that used adipyl-L-leucine as the sole source of L-leucine. DNA sequencing of the mutant pac genes identified a transversion mutation of thymine to guanine at position 1163. This mutation was located in the beta-subunit of the enzyme and resulted in conversion of Phe-360 to valine. The assignment of this mutation to the shift in substrate specificity was further confirmed by site-directed mutagenesis. Secondary-structure prediction of the region surrounding Phe-360 suggests that this mutation should not produce any significant structural change. The purified mutant acylase was able to hydrolyse adipyl-, glutaryl-, valeryl-, caproyl-, heptanoyl- and phenoxyacetyl-L-leucine at pH 5 with greater efficiency than the wild-type enzyme. However, the mutant enzyme was not able to hydrolyse glutaryl-7-aminocephalosporanic acid and had lost 90% and 50% of activity on penicillin G and phenylacetyl-L-leucine respectively. Nevertheless, mutant PA retained its original activity on 6-nitro-3-phenylacetamidobenzoate and p-nitrophenylphenylacetate, suggesting that the binding specificity of PA by the acyl and amine moieties of the substrate are not independent phenomena. The small differences observed between the c.d. spectra of the mutant enzyme recorded at pH 5 and 8 suggest the existence of different conformational states at the two pH values, but these differences were indistinguishable from those observed in the native enzyme and cannot be correlated with the shift in substrate specificity. Our results demonstrate that it is possible to change the specificity of PA by laboratory evolution and use it to identify the amino acids involved in substrate recognition. However, the synchronous participation of the alpha- and beta-subunits in the complex induced-fit-like mechanism of acylases suggests that, to obtain new enzymes for industrial application, the selection pressure should be specifically designed for the compound of interest.

The penicillin amidase of Arthrobacter viscosus (ATCC 15294)

The nucleotide (nt) sequence of the gene encoding penicillin G amidase (PA) of Arthrobacter viscosus strain ATCC 15,294 was determined. The sequence contained an open reading frame of 2406 nt with a G+C content of 37%. The deduced amino-acid sequence shows significant homology with other so far identified beta-lactam amidases of Gram- bacteria.

Studies of operational variables in batch mode for genetically engineered Escherichia coli cells containing penicillin acylase

A recombinant Escherichia coli was constructed by cloning the penicillin acylase gene from E. coli ATCC 11105. The cloning was carried out using a recombinant plasmid pUSAD2 harboring the pac gene. The recombinant E. coli DH 5 cells were used as a biocatalyst and were studied in a batch reactor for determination of optimum value for some of the process parameters, such as effect of pH, temperature, substrate concentration, kLa and effect of carbon and nitrogen source on penicillin acylase production. These values were then compared with the values obtained with the standard parent strain. Whereas the cloned pac gene was found to produce higher levels of penicillin acylase constitutively, the process parameters remained about the same for both the parent and the recombinant.

Inactivation of penicillin acylase from Kluyvera citrophila by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline: a case of time-dependent non-covalent enzyme inhibition

Penicillin acylase (PA) from Kluyvera citrophila was inhibited by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ), a specific carboxy-group-reactive reagent. Enzyme activity progressively decreased to a residual value depending on EEDQ concentration. Neither enzymic nor non-enzymic decomposition of EEDQ is concomitant with PA inactivation. Moreover, enzyme re-activation is achieved by chromatographic removal of EEDQ, pH increase or displacement of the reagent with penicillin G. It was then concluded that PA inactivation is due to an equilibrium reaction. The kinetics of enzyme inactivation was analysed by fitting data to theoretical equations derived in accordance with this mechanism. Corrections for re-activation during the enzyme assay were a necessary introduction. The pH-dependence of the rate constant for EEDQ hydrolysis either alone or in the presence of enzyme was studied by u.v. spectroscopy. It turned out to be coincident with the pH-dependence of the forward and reverse rate constants for the inactivation process. It is suggested that previous protonation of the EEDQ molecule is required for these reactions to occur. The thermodynamic values associated with the overall reaction showed little change. Finally it is proposed that the inactivation of PA by EEDQ proceeds through a two-step reaction. The initial and rapid reversible binding is followed by a slow, time-dependent, non-covalent, reversible inactivating step. The expected behaviour in the case of enzyme modification by covalent activation of carboxy residues is also reviewed.

Morphological, physiological and enzymatic characteristics of cephalosporin acylase-producing Arthrobacter strain 45-8A

A bacterial strain producing cephalosporin acylases was isolated from soil. The morphological and physiological properties of this strain suggest that it belongs to the genus Arthrobacter, and the isolate was therefore designated Arthrobacter strain 45-8A. Substrate specificity of the enzyme was examined. The enzyme can convert both cephalosporin acid to 7-aminocephalosporanic acid. An interesting feature of the acylases is their temperature-dependent regulation. Activity of acylases was detected in strain 45-8A grown at temperature below 30 degrees C, but was not observed at higher temperature. Arthrobacter strain 45-8A did not exhibit beta-lactamase activity, even though its resistance to cephalosporin C was very strong (> 2000 micrograms/ml). This is quite beneficial for its application in the manufacture of 7-aminocephalosporanic acid.

Immobilization studies of an industrial penicillin acylase preparation on a silica carrier

Penicillin acylase (EC 3.5.1.11) was immobilized by covalent binding on a silica gel carrier activated by silanization. High immobilization yields, operational stability, enzyme loading and support reutilization capacity were obtained. The effects of several variables on the activation of the support and on the immobilization method were studied. Other supports and immobilization methods were assessed for the immobilization of penicillin acylase and compared with the basic process used. Activity versus temperature, pH, buffer molarity and penicillin concentration profiles were determined and compared for the free, crosslinked and covalently-bound silica carrier penicillin acylase preparations. The hydrolysis performance of the latter preparation was assessed in a batch basket reactor and the time course of the hydrolysis reaction modelled by a two parameter model equation. The operational stabilities of penicillin acylase coupled covalently to the silica gel support and immobilized by a crosslinking procedure using glutaraldehyde were also compared.

Immobilization of penicillin acylase on copolymer of butyl acrylate and ethylene glycol dimethacrylate

The effects of glutaraldehyde, enzyme concentrations and reactants volumes, ionic strength, pH value and carrier particle diameter on immobilization of penicillin acylase onto acrylic carriers were studied. The activity of immobilized enzyme preparations was also studied over a range of pH values and temperatures and thermal and pH stabilities were determined. The use of the immobilized preparation for penicillin G hydrolysis in a batch reactor was investigated. The immobilized enzyme gave a significant reduction in hydrolysis time compared to hydrolysis by the native enzyme.

Continuous production of 6-APA in an aqueous two-phase system

An aqueous two-phase system of polyethylene glycol (PEG) and potassium phosphate provided a favorable environment for bioconversion of penicillin G to 6-aminopenicillanic acid (6-APA). The recombinant E. coli cells containing penicillin acylase were partitioned in the phosphate-rich bottom phase, and the product 6-APA in the PEG-rich top phase, which protected the enzyme from deactivation for a longer period of time. The continuous production of 6-APA by recycling the bottom phase showed a slight decrease in enzyme activity from initial 80 mM of 6-APA production to 61 mM during the eight days of operation at a space velocity of 0.12 hours-1. This work showed a possibility that the aqueous two-phase whole-cell enzyme bioconversion could serve as an alternative to immobilized cells on solid matrices.

Immobilization of permeabilized Escherichia coli cells with penicillin acylase activity

Escherichia coli cells with penicillin acylase activity were sequentially treated at pH 7.8 with aqueous solutions of N-cetyl-N,N,N-trimethylammonium bromide and glutaraldehyde and then immobilized within porous polyacrylamide beads. The immobilized whole cells showed enhanced hydrolysis rates in the conversion of benzylpenicillin to 6-aminopenicillanic acid (6-APA) compared to untreated cells immobilized and used under identical conditions. The immobilized system showed no apparent loss in enzyme activity when used repeatedly over 90 cycles for 6-APA production from 4% benzylpenicillin.

Carbon regulation and the role in nature of the Escherichia coli penicillin acylase (pac) gene

Quantitative analysis of specific pac mRNA and a lacZ fusion to the 5'-terminal region of the pac gene demonstrated that both phenylacetic acid induction and catabolite repression by glucose are involved, at the transcriptional level, in the regulation of the pac gene. The studies presented here suggest that this regulation is also present in Escherichia coli transformed strains in which the pac gene was not originally present. Analysis of the nucleotide sequence of the 5'-terminal region of this gene, with a statistical algorithm, confirms that the putative promoter previously proposed by our group is the most feasible within this region. We demonstrate that penicillin acylase activity can confer on E. coli the ability to use penicillin G as a metabolic substrate, by detaching the phenylacetic group which can be used as a carbon source. Based on these data, the regulation properties of the pac gene studied in this work, and the specificity profile of the penicillin acylase enzyme we suggest a role for it in E. coli as a scavenger enzyme for phenylacetylated compounds.

Immobilization of penicillin acylase in porous beads of polyacrylamide gel

A procedure is described for the immobilization of benzylpenicillin acylase from Escherichia coli within uniformly spherical, porous polyacrylamide gel beads. Aqueous solutions of the enzyme and sodium alginate and of acrylamide monomer, N,N'-methylene-bis-acrylamide, N,N,N,N'-tetramethylethylenediamine (TEMED) and sodium alginate are cooled separately, mixed, and dropped immediately into ice-cold, buffered calcium formate solution, pH 8.5, to give calcium alginate-coated beads. The beads are left for 30-60 min in the cold calcium formate solution for polyacrylamide gel formation. The beads are then treated with a solution of glutaraldehyde and the calcium alginate subsequently leached out with a solution of potassium phosphate. Modification of the native enzyme with glutaraldehyde results in a slight enhancement in the rate of hydrolysis of benzylpenicillin at pH 7.8 and 0.05M substrate concentration. The enzyme entrapped in porous polyacrylamide gel beads shows no measurable diffusional limitation in stirred reactors, catalyzing the hydrolysis of the substrate at a rate comparable to that of the glutaraldehyde-modified native enzyme. The immobilized enzyme preparation has been used in batch mode over 90 cycles without any apparent loss in hydrolytic activity.

Bead cellulose derivatives as supports for immobilization and chromatographic purification of proteins

Characteristic data are presented for Divicell, a macroporous bead cellulose with excellent flow parameters. The preparation of Divicell derivatives and their properties are described with respect to their application as chromatographic supports. The ion exchangers Divicell DEAE and Divicell CM were manufactured in two types with different exclusion limits and an available capacity for proteins of up to 100 mg/ml gel. Divicell Blue is a bead cellulose with covalently bound Cibacron Blue F3G-A and was found to be a very suitable adsorbent for the selective separation and purification of human serum albumin. Activation of Divicell with sodium periodate, epichlorohydrin and 5-norbornene-2,3-dicarboximido carbonochloridate provided activated supports used for immobilization of ligands in organic solvents and in aqueous solutions. Coupling of amines, diamines, amino acids, carbohydrates and proteins is described. The immobilized ligands retained their biological activity as determined by their specific adsorption of proteins. Divicell alkyl derivatives were tested in hydrophobic interaction chromatography with bovine serum albumin as a model. Examples are presented of the application of Divicell derivatives to the purification of biomacromolecules such as immunoglobulins and lectins by affinity chromatography. The results were comparable to those obtained using the corresponding Sepharose-derived absorbents.