Distribution and substrate specificity of benzylpenicillin acylase

Genomic analysis of the original Elberg Brucella melitensis Rev.1 vaccine strain reveals insights into virulence attenuation

The live attenuated Brucella melitensis Rev.1 Elberg-originated vaccine strain has been widely used to control brucellosis in small ruminants. However, despite extensive research, the molecular mechanisms underlying the attenuation of this strain are still unknown. In the current study, we conducted a comprehensive comparative analysis of the whole-genome sequence of Rev.1 against that of the virulent reference strain, B. melitensis 16M. This analysis revealed five regions of insertion and three regions of deletion within the Rev.1 genome, among which, one large region of insertion, comprising 3,951 bp, was detected in the Rev.1 genome. In addition, we found several missense mutations within important virulence-related genes, which may be used to determine the mechanism underlying virulence attenuation. Collectively, our findings provide new insights into the Brucella virulence mechanisms and, therefore, may serve as a basis for the rational design of new Brucella vaccines.

Metabolism of oral cephalothin and related cephalosporins in the rat

The fate of orally administered [(14)C]cephalothin has been studied in the rat. This antibiotic undergoes degradation in the gut followed by the subsequent absorption of a portion of the degradation products. About 50% of the administered radioactivity appears in the urine as a mixture of thienylacetylglycine, thienylacetamidoethanol and an unidentified polar metabolite. Evidence is presented indicating that thienylacetamidoethanol arises by the enzymic reduction of a metabolic intermediate, thienylacetamidoacetaldehyde. The metabolic fate of cephalothin is very similar to that of cephaloram reported earlier. The fate of [(14)C]cephaloridine and 7-phenoxy[1-(14)C]acetamidocephalosporin was also investigated. In addition to the expected metabolites, about 5% of the cephaloridine dose is absorbed unchanged. With 7-phenoxy[1-(14)C]acetamidocephalosporin, 15% of the dose is recovered in urine as deacetyl-7-phenoxy[1-(14)C]acetamidocephalosporin.

Structure-based prediction of modifications in glutarylamidase to allow single-step enzymatic production of 7-aminocephalosporanic acid from cephalosporin C

Glutarylamidase is an important enzyme employed in the commercial production of 7-aminocephalosporanic acid, a starting compound in the synthesis of cephalosporin antibiotics. 7-aminocephalosporanic acid is obtained from cephalosporin C, a natural antibiotic, either chemically or by a two-step enzymatic process utilizing the enzymes D-amino acid oxidase and glutarylamidase. We have investigated possibilities for redesigning glutarylamidase for the production of 7-aminocephalosporanic acid from cephalosporin C in a single enzymatic step. These studies are based on the structures of glutarylamidase, which we have solved with bound phosphate and ethylene glycol to 2.5 A resolution and with bound glycerol to 2.4 A. The phosphate binds near the catalytic serine in a way that mimics the hemiacetal that develops during catalysis, while the glycerol occupies the side-chain binding pocket. Our structures show that the enzyme is not only structurally similar to penicillin G acylase but also employs essentially the same mechanism in which the alpha-amino group of the catalytic serine acts as a base. A subtle difference is the presence of two catalytic dyads, His B23/Glu B455 and His B23/Ser B1, that are not seen in penicillin G acylase. In contrast to classical serine proteases, the central histidine of these dyads interacts indirectly with the O(gamma) through a hydrogen bond relay network involving the alpha-amino group of the serine and a bound water molecule. A plausible model of the enzyme-substrate complex is proposed that leads to the prediction of mutants of glutarylamidase that should enable the enzyme to deacylate cephalosporin C into 7-aminocephalosporanic acid.

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

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 (alpha-subunit, 205; beta-subunit, 553), all but the eight C-terminal residues of the alpha-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 alpha-subunit and five residues from the beta-subunit has been identified. This enzyme belongs to the superfamily of Ntn hydrolases and uses Ogamma of Ser beta1 as the characteristic N-terminal nucleophile. A mutation of the wild-type Met alpha140 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 alpha-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 beta-lactam R-groups and to function as a cephalosporin acylase and thus be used in the manufacture of semi-synthetic cephalosporins.

Ligand-induced conformational change in penicillin acylase

The enzyme penicillin acylase (penicillin amidohydrolase EC 3.5.1. 11) catalyses the cleavage of the amide bond in the benzylpenicillin (penicillin G) side-chain to produce phenylacetic acid and 6-aminopenicillanic acid (6-APA). The enzyme is of great pharmaceutical importance, as the product 6-APA is the starting point for the synthesis of many semi-synthetic penicillin antibiotics. Studies have shown that the enzyme is specific for hydrolysis of phenylacetamide derivatives, but is more tolerant of features in the rest of the substrate. It is this property that has led to many other applications for the enzyme, and greater knowledge of the enzyme's structure and specificity could facilitate engineering of the enzyme, enhancing its potential for chemical and industrial applications. An extensive study of the binding of a series of phenylacetic acid derivatives has been carried out. A measure of the relative degree of inhibition of the enzyme by each of the compounds has been obtained using a competitive inhibition assay, and the structures of a number of these complexes have been determined by X-ray crystallography. The structures reveal a clear rationale for the observed kinetic results, but show also that some of the ligands cause a conformational change within the binding pocket. This change can generally be understood in terms of the size and orientation of the ligand within the active site.The results reveal that ligand binding in penicillin acylase is facilitated by certain amino acid residues that can adopt two distinct, energetically favourable positions in order to accommodate a variety of compounds within the active site. The structures of these complexes provide evidence for conformational changes in the substrate-binding region that may act as a switch in the mechanism of autocatalytic processing of this enzyme.

PRODUCTION OF PENICILLIN ACYLASE

The production of penicillin acylase by Escherichia coli Ny.I/3-67 has been increased by phenylacetic acid and phenoxyacetic acid, which themselves strongly inhibit the function of this specific enzyme. Other carbonic acids also increased penicillin acylase production, but to a lesser degree; they also weakly inhibited enzyme function. The production of this enzyme was effectively repressed with metabolic carbohydrates and polyalcohols. Because enzyme production is dependent upon temperature, an increase in the temperature of incubation (above 31 C) decreased production of the enzyme, and increased the repressive effect of carbohydrates and polyalcohols.

ENZYMATIC DEACYLATION OF S35-BENZYLPENICILLIN

Pruess, David L. (University of Wisconsin, Madison), and Marvin J. Johnson. Enzymatic deacylation of S(35)-benzylpenicillin. J. Bacteriol. 90:380-383. 1965.-S(35)-benzylpenicillin, penicilloic acid, and penilloic acid were deacylated by cell suspensions of Escherichia coli and Micrococcus roseus. Both cultures deacylated penicillin most rapidly and penilloic acid least rapidly. The deacylase activity of M. roseus against penicilloic acid was cell-bound, probably requiring a metal ion for activity.

Purification and preliminary crystallographic studies of penicillin G acylase from Providencia rettgeri

Two isoforms of the heterodimeric enzyme penicillin G acylase (EC 3.5.1.11) from Providencia rettgeri ATCC 31052 (strain Bro1) were purified to near homogeneity. The isoforms exhibited comparable enzymatic activities but differed slightly in the molecular weight and pI of their respective alpha-subunit. The origin of this difference was traced to the partial conversion of the N-terminal Gln of the alpha-subunit to pyrrolidonecarboxylic acid (pyro-Glu). The boundaries of the mature enzyme within the translated DNA sequence of the wild-type propeptide (GenBank M86533) were determined. The results conclusively identified the length of the signal peptide and the position of the spacer cleaved from the propeptide to form the active heterodimer. The molecular weights of the alpha- and beta-subunits, based on these termini, were 23.7 and 62.2 kDa, respectively. Both isoforms were crystallized independently as hexagonal bipyramids up to 0.60 mm in diameter in either space group P6(1)22 or P6(5)22 (a = b = 140.5 A and c = 209.5 A) from ammonium sulfate solutions buffered by 50 mM potassium phosphate at pH 7.5. The presence of glycerol, although not required, facilitated crystal growth. Native and heavy atom derivative data were collected to 3.0 A resolution, and the calculation of isomorphous replacement phases is under way.

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.

Cephalosporin C acylase in the autolysis of filamentous fungi

Cephalosporin C acylase activity was studied using fluorescamine determination of free--NH2 groups produced in the deacylation of cephalosporin C by the enzyme. Fourteen fungi from different genera were studied and low extracellular cephalosporin C acylase activity was found in the genera Aspergillus, Fusarium and Penicillium. Forty one fungi of these genera were checked but not all presented acylase activity. The enzyme was generally found to be an extracellular enzyme and during the process of autolysis its activity increased with incubation time and with increasing pH of the medium. In no case was beta-lactamase activity detected. Penicillium rugulosum and Penicillium griseofulvum were identified as good cephalosporin C acylase producers. Deacetyl esterase activity was also detected in these fungi.

Experimental evolution of penicillin G acylases from Escherichia coli and Proteus rettgeri

Proteus rettgeri and Escherichia coli W were shown to express structurally different penicillin G acylases. The enzymes had similar substrate specificity but differed in molecular weight, isoelectric point, and electrophoretic mobility in polyacrylamide gels and did not antigenically cross-react. When the organisms were subjected to environmental conditions which made expression of this enzyme essential for growth, spontaneous mutants were isolated that used different amides as the only source of nitrogen. These mutants acquired the ability to use amides for growth by deregulating the penicillin G acylase and by their evolution to novel substrate specificities. The enzymes expressed by mutants isolated from each genus appeared to have evolved in parallel since each acylase attained similar new substrate specificities when the organisms were subjected to identical selection pressure.

Biochemical properties of penicillin amidohydrolase from Micrococcus luteus

Some biochemical properties of whole-cell penicillin amidohydrolase from Micrococcus luteus have been studied. This whole-cell enzyme showed its maximal activity at 36 degrees C at pH 7.5. It was found that the activation energy of this enzyme was 8.03 kcal (ca. 33.6 kJ) per mol, and this amidohydrolase showed first-order decay at 36 degrees C. The penicillin amidohydrolase was deactivated rapidly at temperatures above 50 degrees C during storage or preincubation for 24 h. The Michaelis constant, Km, for penicillin G was determined as 2.26 mM, and the substrate inhibition constant, Kis, was 155 mM. The whole-cell penicillin amidohydrolase from M. luteus was capable of hydrolyzing penicillin G, penicillin V, ampicillin, and cephalexin, but not cephalosporin C and cloxacillin. This whole-cell enzyme also had synthetic activity for semisynthetic penicillins or cephalosporins from D-(--)-alpha-phenylglycine methyl ester and 6-alpha-aminopenicillanic acid or 7-amino-3-deacetoxycephalosporanic acid.

Hydrolysis of penicillins and related compounds by the cell-bound penicillin acylase of Escherichia coli

1. A method is given for the preparation of penicillin acylase by using Escherichia coli N.C.I.B. 8743 and a strain selected for higher yield. The enzyme is associated with the bacterial cells and removes the side chains of penicillins to give 6-amino-penicillanic acid and a carboxylic acid. 2. The rates of penicillin deacylation indicated that p-hydroxybenzylpenicillin was the best substrate, followed in diminishing order by benzyl-, dl-alpha-hydroxybenzyl-, 2-furylmethyl-, 2-thienylmethyl-, d-alpha-aminobenzyl-, n-propoxymethyl- and isobutoxymethyl-penicillin. Phenylpenicillin and dl-alpha-carboxybenzylpenicillin were not substrates and phenoxymethyl-penicillin was very poor. 3. Amides and esters of the above penicillins were also substrates for the deacylation reaction, as were cephalosporins with a thienylmethyl side chain. 4. For the deacylation of 2-furylmethylpenicillin at 21 degrees the optimum pH was 8.2. The optimum temperature was 60 degrees at pH7. 5. By using selection A of N.C.I.B. 8743 and determining reaction velocities by assaying yields of 6-amino-penicillanic acid in a 10min. reaction at 50 degrees and pH8.2, the K(m) for benzylpenicillin was found to be about 30mm and the K(m) for 2-furylmethylpenicillin, about 10mm. The V(max.) values were 0.6 and 0.24mumole/min./mg. of bacterial cells respectively.

Specificity of penicillin acylase of Fusarium and of Penicillium chrysogenum

Extracts containing penicillin acylase were obtained by shaking the mycelium of Fusarium avenaceum and of Penicillium chrysogenum in 0.2 M sodium acetate or sodium chloride solution. The optimum pH for conversion of penicillin V into 6-aminopenicillanic acid (6-APA) by the enzyme of Fusarium was about 7.5, and the reaction velocity was increased by a rise in temperature from 27 to 37 C. Penicillin G and penicillins with an aliphatic side chain were cleaved much less readily than was penicillin V. With the enzyme preparation obtained from a nonpenicillin-producing strain of P. chrysogenum, the reaction rate was higher at pH 8.5 than at pH 7.5 and pH 6.5. The acylase of P. chrysogenum hydrolyzes penicillin V more readily than penicillin G. In a series of aliphatic penicillins, the amount of 6-APA formed through the action of this enzyme increased with the number of carbon atoms of the side chain. Penicillins with a glutaryl or an adipyl group as side chain were unaffected by the enzyme of Fusarium and of Penicillium. No reaction was observed upon incubation of penicillin N (with a D-aminoadipyl side chain) or isopenicillin N (with an L-aminoadipyl side chain) with Fusarium and Penicillium extract. When the carboxy group of the side chain of these penicillins was esterified, formation of 6-APA was observed upon incubation with Penicillium extract, whereas no 6-APA or only very small amounts were obtained by acylase of Fusarium.

Purification and properties of penicillin amidase from Bacillus megaterium

A penicillin amidase, obtained from the exogenous medium of a Bacillus megaterium culture, was purified approximately 96-fold by means of two cycles of adsorption on, and elution from, Celite, followed by a further fractionation on carboxymethylcellulose. On the basis of sedimentation centrifugation analysis, the final preparation was deemed to be homogeneous with an apparent molecular weight of approximately 120,000. The enzyme is specific for benzylpenicillin and has a pH optimum between 8 and 9. Complete hydrolysis of benzylpenicillin was obtained at low substrate concentrations. At higher substrate concentrations, the hydrolysis of benzylpenicillin was incomplete, apparently due to enzyme inhibition by phenylacetic acid and 6-aminopenicillanic acid, which were formed during the hydrolysis. Under the assay conditions, phenylacetic acid was a competitive inhibitor of penicillin amidase with an inhibitor constant (K(i)) of 0.45 m, whereas 6-aminopenicillanic acid was noncompetitive in nature with a K(i) of 2.6 x 10(-2)m. The Michaelis constant of this enzyme was found to be 4.5 x 10(-3)m when benzylpenicillin was used as substrate.

Penicillin acylase activity of Penicillium chrysogenum

The penicillin acylase activity of Penicillium chrysogenum was studied. Washed mycelial suspensions of a high penicillin-producing and a nonproducing strain were found to be similar in respect to relative acylase activity on benzylpenicillin, 2-pentenylpenicillin, heptylpenicillin, and phenoxymethylpenicillin. The relative rates for both strains, as determined by 6-aminopenicillanic acid formation, were approximately 1.0, 2.5, 3.5, and 6.0 on the penicillins in the order given. The high producing strain formed both 6-aminopenicillanic acid and "natural" penicillins in fermentations to which no side-chain precursor had been added. Therefore, its demonstrated ability to cleave the natural penicillins, 2-pentenylpenicillin and heptylpenicillin, suggests that at least some of the 6-aminopenicillanic acid produced during such fermentations arises from the hydrolysis of the natural penicillins. At pH 8.5, the mycelial acylase activity of the nonproducing strain was about three times that at pH 6.0; at 35 C, it was about 1.5 times as active as it was at 30 C. When tested on penicillin G or V, no differences in either total or specific penicillin acylase activity were observed among mycelia harvested from cultures of the nonproducer to which penicillin G, penicillin V, or no penicillin had been added. Acetone-dried mycelium from both strains displayed acylase activity, but considerably less than that shown by viable mycelium. Culture filtrates were essentially inactive, although a very low order of activity was detected when culture filtrate from the nonproducer was treated with acetone and the acetone-precipitated material was assayed in a minimal amount of buffer.

Cephalosporinase and penicillinase activities of a beta-lactamase from Pseudomonas pyocyanea

1. Pseudomonas pyocyanea N.C.T.C. 8203 produces a beta-lactamase that is inducible by high concentrations of benzylpenicillin or cephalosporin C. Methicillin appeared to be a relatively poor inducer, but this could be attributed in part to its ability to mask the enzyme produced. Much of the enzyme is normally cell-bound. 2. No evidence was obtained that the crude enzyme preparation consisted of more than one beta-lactamase and the preparation appeared to contain no significant amount of benzylpenicillin amidase or of an acetyl esterase. 3. The maximum rate of hydrolysis of cephalosporin C and several other derivatives of 7-aminocephalosporanic acid by the crude enzyme was more than five times that of benzylpenicillin. Methicillin, cloxacillin, 6-aminopenicillanic acid and 7-aminocephalosporanic acid were resistant to hydrolysis, and methicillin and cloxacillin were powerful competitive inhibitors of the action of the enzyme on easily hydrolysable substrates. 4. Cephalosporin C, cephalothin and cephaloridine yielded 2 equiv. of acid/mole on enzymic hydrolysis, and deacetylcephalorsporin C yielded 1 equiv./mole. Evidence was obtained that the opening of the beta-lactam ring of cephalosporin C and cephalothin is accompanied by the spontaneous expulsion of an acetoxy group and that of cephaloridine by the expulsion of pyridine. 5. A marked decrease in the minimum inhibitory concentration of benzylpenicillin and several hydrolysable derivatives of 7-aminocephalosporanic acid was observed when the size of the inoculum was decreased. This suggested that the production of a beta-lactamase contributed to the factors responsible for the very high resistance of Ps. pyocyanea to these substances. It was therefore concluded that the latter might show synergism with the enzyme inhibitors, methicillin and cloxacillin, against this organism.