Showing papers on "Penicillin amidase published in 1999"

Crystal structure of penicillin G acylase from the Bro1 mutant strain of Providencia rettgeri.

Abstract: Penicillin G acylase is an important enzyme in the commercial production of semisynthetic penicillins used to combat bacterial infections. Mutant strains of Providencia rettgeri were generated from wild-type cultures subjected to nutritional selective pressure. One such mutant, Bro1, was able to use 6-bromohexanamide as its sole nitrogen source. Penicillin acylase from the Bro1 strain exhibited an altered substrate specificity consistent with the ability of the mutant to process 6-bromohexanamide. The X-ray structure determination of this enzyme was undertaken to understand its altered specificity and to help in the design of site-directed mutants with desired specificities. In this paper, the structure of the Bro1 penicillin G acylase has been solved at 2.5 A resolution by molecular replacement. The R-factor after refinement is 0.154 and R-free is 0.165. Of the 758 residues in the Bro1 penicillin acylase heterodimer (α-subunit, 205; β-subunit, 553), all but the eight C-terminal residues of the α-subunit have been modeled based on a partial Bro1 sequence and the complete wild-type P. rettgeri sequence. A tightly bound calcium ion coordinated by one residue from the α-subunit and five residues from the β-subunit has been identified. This enzyme belongs to the superfamily of Ntn hydrolases and uses Oγ of Serβ1 as the characteristic N-terminal nucleophile. A mutation of the wild-type Metα140 to Leu in the Bro1 acylase hydrophobic specificity pocket is evident from the electron density and is consistent with the observed specificity change for Bro1 acylase. The electron density for the N-terminal Gln of the α-subunit is best modeled by the cyclized pyroglutamate form. Examination of aligned penicillin acylase and cephalosporin acylase primary sequences, in conjunction with the P. rettgeri and Escherichia coli penicillin acylase crystal structures, suggests several mutations that could potentially allow penicillin acylase to accept charged β-lactam R-groups and to function as a cephalosporin acylase and thus be used in the manufacture of semi-synthetic cephalosporins.

Stability and stabilisation of penicillin acylase

Abstract: The stability of an oligomeric enzyme, penicillin acylase, was studied in aqueous media. The enzyme was produced by mutant cells of Escherichia coli ATCC 9637, extracted from the periplasmic space by osmotic shock and further purified using a pseudo-affinity adsorption process. Enzyme stabilisation attempts were performed with salts, alcohols and sugars. The highest levels of retained activity were obtained in the presence of 15% (w/v) ammonium or sodium sulfate. A kinetic model was proposed to describe the inactivation of penicillin acylase, taking into account results obtained in stability assays performed at different temperatures and with different enzyme concentrations. According to this model, the inactivation of penicillin acylase involves an intermediary active precursor of the enzyme, formed prior to dissociation into sub-units.

Processing and functional display of the 86 kDa heterodimeric penicillin G acylase on the surface of phage fd

Abstract: The large heterodimeric penicillin G acylase from Alcaligenes faecalis was displayed on the surface of phage fd. We fused the coding sequence (alpha subunit-internal peptide-beta subunit) to the gene of a phage coat protein. A modified g3p signal sequence was used to direct the polypeptide to the periplasm. Here we show that a heterodimeric enzyme can be expressed as a fusion protein that matures to an active biocatalyst connected to the coat protein of phage fd, resulting in a phage to which the beta-subunit is covalently linked and the alpha-subunit is non-covalently attached. The enzyme can be displayed either fused to the minor coat protein g3p or fused to the major coat protein g8p. In both cases the penicillin G acylase on the phage has the same Michaelis constant as its freely soluble counterpart, indicating a proper folding and catalytic activity of the displayed enzyme. The display of the heterodimer on phage not only allows its further use in protein engineering but also offers the possibility of applying this technology for the excretion of the enzyme into the extracellular medium, facilitating purification of the protein. With the example of penicillin acylase the upper limit for a protein to become functionally displayed by phage fd has been further explored. Polyvalent display was not observed despite the use of genetic constructs designed for this aim. These results are discussed in relation to the pore size being formed by the g4p multimer.

Hydrogen bonding and protein perturbation in beta -lactam acyl-enzymes of streptococcus pneumoniae penicillin-binding protein pbp2x

Abstract: A soluble form of Streptococcus pneumoniae PBP2x, a molecular target of penicillin and cephalosporin antibiotics, has been expressed and purified. IR difference spectra of PBP2x acylated with benzylpenicillin, cloxacillin, cephalothin and ceftriaxone have been measured. The difference spectra show two main features. The ester carbonyl vibration of the acyl-enzyme is ascribed to a small band between 1710 and 1720 cm-1, whereas a much larger band at approx. 1640 cm-1 is ascribed to a perturbation in the structure of the enzyme, which occurs on acylation. The protein perturbation has been interpreted as occurring in beta-sheet. The acyl-enzyme formed with benzylpenicillin shows the lowest ester carbonyl vibration frequency, which is interpreted to mean that the carbonyl oxygen is the most strongly hydrogen-bonded in the oxyanion hole of the antibiotics studied. The semi-synthetic penicillin cloxacillin is apparently less well organized in the active site and shows two partially overlapping ester carbonyl bands. The penicillin acyl-enzyme has been shown to deacylate more slowly than that formed with cloxacillin. This demonstrates that the natural benzylpenicillin forms a more optimized and better-bonded acyl-enzyme and that this in turn leads to the stabilization of the acyl-enzyme required for effective action in the inhibition of PBP2x. The energetics of hydrogen bonding in the several acyl-enzymes is discussed and comparison is made with carbonyl absorption frequencies of model ethyl esters in a range of organic solvents. A comparison of hydrolytic deacylation with hydroxaminolysis for both chymotryspin and PBP2x leads to the conclusion that deacylation is uncatalysed.

Penicillin G amidase in low-water media: immobilisation and control of water activity by means of celite rods

Abstract: Penicillin G amidase (PGA) adsorbed on Celite rods (Celite R-640 from Fluka) catalyses, in toluene, the synthesis of amide bonds with yields >98% using equimolar concentrations of reactants. The method allows the easy recovery of the product and the recycling of the catalyst. Experimental data have pointed out that Celite rods adsorb water in a unusual but useful way, maintaining the water activity of the reaction system constant within defined ranges of water concentrations. Adsorption isotherms of Celite rods are reported and further applications of the method are proposed.

Novel strategy for efficient screening and construction of host/vector systems to overproduce penicillin acylase in Escherichia coli.

Abstract: A novel and simple method of using penicillin for screening of mutant strains with a high penicillin acylase (PAC) activity was developed. Random mutagenesis was conducted using a PAC-producing strain resistant to 6-aminopenicillanic acid (6-APA) as the parent strain and mutants were screened with penicillin at a high concentration. Results suggest that mutants with a high minimum inhibitory concentration for penicillin (MIC(penG)) usually overproduce PAC. Both volumetric and specific PAC activities of a mutant, MD7, were significantly higher than those of the parent strain, HBPAC101 harboring pCLL2902. The mutation(s) resulting in the enhanced expression was mapped on the host chromosome rather than the plasmid. In addition, the mutant strain of MDDeltaP7, derived by elimination of the harbored plasmid in MD7, was demonstrated to be efficient in production of PAC by using the expression plasmids for which expression of the pac gene is limited by translation. An extremely high specific PAC activity of more than 350 U/L/OD(600) was reached upon cultivation of MDDeltaP7 harboring pTrcKnPAC2902 in a bioreactor. As such, the strategy is effective in terms of constructing PAC overproducers and improving the process yield for production of PAC.

β-lactamase-free penicillin amidase from Alcaligenes sp. : Isolation strategy, strain characteristics, and enzyme immobilization

Abstract: Isolation and characterization of a β-lactamase (EC 3.5.2.6)-free, penicillin amidase (penicillin amidohydrolase, EC 3.5.1.11)-producing organism is reported. The test strain was isolated by an enrichment technique with a substrate other than penicillins. The isolated strain belongs to the genus Alcaligenes. Phenylacetic acid was found to be the inducer of penicillin amidase. The amidase has a broad substrate spectrum. It is very active against penicillin G and semisynthetic cephalosporins, whereas penicillin V and semisynthetic penicillins acted moderately as a substrate. Immobilized cells of Alcaligenes sp. were shown to act as a reversible enzyme.

Rapid continuous colorimetric enzyme assay for penicillin G acylase

Abstract: A rapid, continuous, colorimetric enzyme assay for penicillin G acylase has been developed. The assay measures the formation of the acidic products of penicillin G hydrolysis by following the decrease in pH using Phenol Red as an indicator. The activity measured is directly proportional to the amount of enzyme added to the assay, having a linear relationship with an R 2 value of 0.9994.

Electrically immobilized enzyme reactors: bioconversion of a charged substrate. Hydrolysis Of penicillin G by penicillin G acylase.

Abstract: The possibility of using the multicompartment immobilized enzyme reactor (MIER) in presence of a charged substrate is here explored. Penicillin G acylase is used to convert penicillin G (a free acid, with a pK of 2.6) into two charged products: phenyl acetic acid (PAA, with a pK of 4.2) and 6-aminopenicillanic acid (6-APA, a zwitterion with a pI of 3.6). The enzyme is trapped by an isoelectric mechanism in a chamber of the electrolyzer delimited by a pI 5.0 and a pI 9.0 amphoteric, isoelectric membranes. Under normal operating conditions (continuous substrate feeding in the presence of an electric field), only a low substrate conversion can be achieved, due to rapid electrophoretic transport of unreacted penicillin G out of the reaction chamber towards the anode. Excellent conversion rates (>96%) are obtained under a "doubly-discontinuous" operation mode: a time-lapse substrate feeding, accompanied by short times (4-8 min) of electric field interruption. The product of interest (6-APA, a precursor of semisynthetic penicillins), by virtue of its amphoteric nature, is trapped in a chamber delimited by a pI 3.5 membrane and a pI 5.5 membrane, adjacent to the reaction chamber on its anodic side. The other contaminant product (PAA) first accumulates in the same chamber and then progressively vacates it to collect in the anodic reservoir, leaving behind a pure 6-APA solution. In this operation mode, vanishing amounts of unreacted substrate (penicillin G) leave the reaction chamber to contaminate the adjacent, anodic chambers. A novel class of zwitterionic buffers is additionally reported, able to cover very thoroughly any pH value along the pH 3-10 interval: polymeric, zwitterionic buffers, synthesized with the principle of the Immobiline (acrylamido weak acids and bases) chemicals. Enhanced enzyme reactivity is found in this macromolecular buffers as compared to conventional ones.

Effect of dextran polymers on the stability of soluble Escherichia coli penicillin G acylase

Abstract: The stabilisation of Escherichia coli penicillin G acylase (PGA) by dextran polymers (of molecular weight 11.5, 37.7 and 71kDa) was studied. The inactivation of both the native and dextran-containing enzyme preparations obeyed first-order kinetics at the temperature and pH values studied. The optimal concentrations of dextran polymers of molecular weight 11.5, 37. 7 and 71 kDa stabilising PGA against inactivation were 50, 20 and 7.5 mmol dm -3 respectively. Dextran 11500 (11.5kDa) gave 100-fold protection of PGA against thermal inactivation of enzyme above 50 °C. The kinetic constants of the enzyme were slightly altered, but temperature and pH profiles were not altered by the dextrans.

Synthesis of beta-lactam antibiotics with immobilized penicillin amidase

Abstract: Beta-lactam antibiotics are synthesized by reacting an amino-beta-lactam component with a corresponding amino-group-containing acylating side-chain component in the presence of penicillin amidase from E. coli covalently immobilized on support particles. The resulting beta-lactam antibiotic product is solubilized by adding an acid such as sulfuric acid to lower the pH to 1.0 at a temperature in the range of 0° C. to +5° C. The immobilized penicillin amidase is substantially inactivated by the acid. After separating the beta-lactam antibiotic product, the immobilized penicillin amidase is substantially reactivated for reuse in antibiotic synthesis by treatment with a buffer having about a neutral pH. Antibiotics that can be produced include ampicillin, amoxicillin, cephalexin, cefaclor and cefadroxil. Support particles that can be used include particles having a macroporous structure and a particle diameter of 10-1000 μm, particles having oxirane groups, particles made of a synthetic polymer and inorganic particles such as porous glass particles.

Optimization of a pseudo-affinity process for penicillin acylase purification

Abstract: A pseudo-affinity process for penicillin acylase (EC 3.5.1.11) purification using an affinity ligand (Ampicillin) attached on Sepharose 4B-CNBr was optimized. The enzyme adsorption on this affiant (Amp-Seph) is independent of pH between 5.5 and 8.8, in 100 mM phosphate containing 22% (w/v) ammonium sulphate. The desorption of the penicillin acylase from the affinity gels was carried out, the best desorption results being obtained through a non specific eluent, 100 mM phosphate pH 4.6 with 15% (w/v) ammonium sulphate. The best purification results were obtained with an enzymatic extract, produced through osmotic shock of Escherichia coli cells (3.7 IU/mg prot). With this extract and an affinity gel of Sepharose 4B-CNBr derivatized with ampicillin (3.8 μmol/cm3 gel), a maximum activity capacity adsorbed of 20 IU/cm3 gel was obtained for initial values of activity and protein concentration of 1.7 IU/cm3 and 0.4 mg prot/cm3, respectively. With the optimized eluent it was possible to obtain penicillin acylase in only one purification step with a desorption yield of enzyme activity higher than 90%. The penicillin acylase produced with this process was characterized by a maximum purity of 34 IU/mg prot, corresponding to a purification degree higher than 150 in relation to the lowest pure enzymatic extract. The enzyme purity of the eluted fractions was certified by SDS gel electrophoresis and liquid chromatography through a Mono Q column in a FPLC apparatus. The gel electrophoresis presented 4 main stained bands with 2 corresponding to α and β subunits of the penicillin acylase with equivalent molecular weights of 27 and 63 kDa. No external diffusion resistance on penicillin acylase and total protein adsorption on this affiant (Amp-Seph 3.8 μmol/cm3 gel) were observed for continuous adsorption processes performed at two different agitation speeds (120 and 400 rpm).