Microbial penicillin acylases

Enzymes From Rare Actinobacterial Strains

Actinobacteria constitute rich sources of novel biocatalysts and novel natural products for medical and industrial utilization. Although actinobacteria are potential source of economically important enzymes, the isolation and culturing are somewhat tough because of its extreme habitats. But now-a-days, the rate of discovery of novel compounds producing actinomycetes from soil, freshwater, and marine ecosystem has increased much through the developed culturing and genetic engineering techniques. Actinobacteria are well-known source of their bioactive compounds and they are the promising source of broad range of industrially important enzymes. The bacteria have the capability to degrade a range of pesticides, hydrocarbons, aromatic, and aliphatic compounds (Sambasiva Rao, Tripathy, Mahalaxmi, & Prakasham, 2012). Most of the enzymes are mainly derived from microorganisms because of their easy of growth, minimal nutritional requirements, and low-cost for downstream processing. The focus of this review is about the new, commercially useful enzymes from rare actinobacterial strains. Industrial requirements are now fulfilled by the novel actinobacterial enzymes which assist the effective production. Oxidative enzymes, lignocellulolytic enzymes, extremozymes, and clinically useful enzymes are often utilized in many industrial processes because of their ability to catalyze numerous reactions. Novel, extremophilic, oxidative, lignocellulolytic, and industrially important enzymes from rare Actinobacterial population are discussed in this chapter.

Structure mediation in substrate binding and post-translational processing of penicillin acylases: Information from mutant structures of Kluyvera citrophila penicillin G acylase

Penicillin acylases are industrially important enzymes for the production of 6-APA, which is used extensively in the synthesis of secondary antibiotics. The enzyme translates into an inactive single chain precursor that subsequently gets processed by the removal of a spacer peptide connecting the chains of the mature active heterodimer. We have cloned the penicillin G acylase from Kluyvera citrophila (KcPGA) and prepared two mutants by site-directed mutagenesis. Replacement of N-terminal serine of the β-subunit with cysteine (Serβ1Cys) resulted in a fully processed but inactive enzyme. The second mutant in which this serine is replaced by glycine (Serβ1Gly) remained in the unprocessed and inactive form. The crystals of both mutants belonged to space group P1 with four molecules in the asymmetric unit. The three-dimensional structures of these mutants were refined at resolutions 2.8 and 2.5 Å, respectively. Comparison of these structures with similar structures of Escherichia coli PGA (EcPGA) revealed various conformational changes that lead to autocatalytic processing and consequent removal of the spacer peptide. The large displacements of residues such as Arg168 and Arg477 toward the N-terminal cleavage site of the spacer peptide or the conformational changes of Arg145 and Phe146 near the active site in these structures suggested probable steps in the processing dynamics. A comparison between the structures of the processed Serβ1Cys mutant and that of the processed form of EcPGA showed conformational differences in residues Argα145, Pheα146, and Pheβ24 at the substrate binding pocket. Three conformational transitions of Argα145 and Pheα146 residues were seen when processed and unprocessed forms of KcPGA were compared with the substrate bound structure of EcPGA. Structure mediation in activity difference between KcPGA and EcPGA toward acyl homoserine lactone (AHL) is elucidated.

Penicillin acylases revisited: importance beyond their industrial utility

It is of great importance to study the physiological roles of enzymes in nature; however, in some cases, it is not easily apparent. Penicillin acylases are pharmaceutically important enzymes that cleave the acyl side chains of penicillins, thus paving the way for production of newer semi-synthetic antibiotics. They are classified according to the type of penicillin (G or V) that they preferentially hydrolyze. Penicillin acylases are also used in the resolution of racemic mixtures and peptide synthesis. However, it is rather unfortunate that the focus on the use of penicillin acylases for industrial applications has stolen the spotlight from the study of the importance of these enzymes in natural metabolism. The penicillin acylases, so far characterized from different organisms, show differences in their structural nature and substrate spectrum. These enzymes are also closely related to the bacterial signalling phenomenon, quorum sensing, as detailed in this review. This review details studies on biochemical and structural characteristics of recently discovered penicillin acylases. We also attempt to organize the available insights into the possible in vivo role of penicillin acylases and related enzymes and emphasize the need to refocus research efforts in this direction.

Strategies for enhancing the production of penicillin G acylase from Bacillus badius: influence of phenyl acetic acid dosage

Bacillus badius isolated from soil has been identified as potential producer of penicillin G acylase (PGA). In the present study, batch experiments performed at optimized inoculum size, temperature, pH, and agitation yielded a maximum PGA of 9.5 U/ml in shake flask. The experiments conducted in bioreactor with different oxygen flow rates revealed that 0.66 vvm oxygen flow rate could be sufficient for the maximum PGA activity of 12.7 U/ml. From a detailed investigation on the strategies of the addition of phenyl acetic acid (PAA) for increasing the production of PGA, it was found that the controlled addition of 10 ml of 0.1 % (w/v) PAA once in every 2 h from 6th hour of growth showed the maximum PGA activity of 32 U/ml. Thus, our studies for the first time showed that at concentration above 0.1 % (w/v) PAA, the PGA production decreased. This selective condition paves the way for less costly bioprocess for the production of PGA.

Improved penicillin amidase production using a genetically engineered mutant of Escherichia coli ATCC 11105

Penicillin G amidase (PGA) is a key enzyme for the industrial production of penicillin G derivatives used in therapeutics. Escherichia coli ATCC 11105 is the more commonly used strain for PGA production. To improve enzyme yield, we constructed various recombinant E. coli HB101 and ATCC 11105 strains. For each strain, PGA production was determined for various concentrations of glucose and phenylacetic and (PAA) in the medium. The E. coli strain, G271, was identified as the best performer (800 U NIPAB/L). This strain was obtained as follows: an E. coli ATCC 11105 mutant (E. coli G133) was first selected based on a low negative effect of glucose on PGA production. This mutant was then transformed with a pBR322 derivative containing the PGA gene. Various experiments were made to try to understand the reason for the high productivity of E. coli G271. The host strain, E. coli G133, was found to be mutated in one (or more) gene(s) whose product(s) act(s) in trans on the PGA gene expression. Its growth is not inhibited by high glucose concentration in the medium. Interestingly, whereas glucose still exerts some negative effect on the PGA production by E. coli G133, PGA production by its transformant (E. coli G271) is stimulated by glucose. The reason for this stimulation is discussed. Transformation of E. coli G133 with a pBR322 derivative containing the Hindlll fragment of the PGA gene, showed that the performance of E. coli G271 depends both upon the host strain properties and the plasmid structure. Study of the production by the less efficient E. coli HB101 derivatives brought some light on the mechanism of regulation of the PGA gene.

Mutagenic effect of acridine orange on the expression of penicillin G acylase and beta-lactamase in Escherichia coli

AIMS

The present work aimed to improve the production of penicillin G acylase (PGA) and reduce the beta-lactamase activity through acridine orange (AO) induced mutation in Escherichia coli.

METHODS AND RESULTS

Three wild E. coli strains BDCS-N-FMu10, BDCS-N-S21 and BDCS-N-W50, producing both the enzymes PGA and beta-lactamase were treated by AO. Minimum inhibitory concentration of AO was 10 microg ml(-1) and it was noted that bacterial growth was gradually suppressed by increasing the concentration of AO from 10 to 100 microg ml(-1). The highest concentration that gave permissible growth rate was 50 microg ml(-1). The isolated survivals were screened on the bases of PGA and beta-lactamase activities. Among the retained mutants, the occurrence of beta-lactamase deficient ones (91%) was significantly higher than penicillin acylase deficient ones (27%).

CONCLUSIONS

In seven of the mutants, PGA activity was enhanced with considerable decrease in beta-lactamase activity. One of the mutant strains (BDCS-N-M36) exhibited very negligible expression of beta-lactamase activity and twofold increase in PGA activity [12.7 mg 6-amino-penicillanic acid (6-APA) h(-1) mg(-1) wet cells] compared with that in the wild-type strain (6.3 mg 6-APA h(-1) mg(-1) wet cells).

SIGNIFICANCE AND IMPACT OF THE STUDY

The treatment of E. coli cells with AO resulted in mutants with enhanced production of PGA and inactivation of beta-lactamase. These mutants could be used for industrial production of PGA.

Fast and efficient protein purification using membrane adsorber systems

The purification of proteins from complex cell culture samples is an essential step in proteomic research. Traditional chromatographic methods often require several steps resulting in time consuming and costly procedures. In contrast, protein purification via membrane adsorbers offers the advantage of fast and gentle but still effective isolation. In this work, we present a new method for purification of proteins from crude cell extracts via membrane adsorber based devices. This isolation procedure utilises the membranes favourable pore structure allowing high flow rates without causing high back pressure. Therefore, shear stress to fragile structures is avoided. In addition, mass transfer takes place through convection rather than diffusion, thus allowing very rapid separation processes. Based on this membrane adsorber technology the separation of two model proteins, human serum albumin (HSA) and immungluboline G (IgG) is shown. The isolation of human growth hormone (hGH) from chinese hamster ovary (CHO) cell culture supernatant was performed using a cation exchange membrane. The isolation of the enzyme penicillin acylase from the crude Escherichia coli supernatant was achieved using an anion exchange spin column within one step at a considerable purity. In summary, the membrane adsorber devices have proven to be suitable tools for the purification of proteins from different complex cell culture samples.

The PaaX repressor, a link between penicillin G acylase and the phenylacetyl-coenzyme A catabolon of Escherichia coli W

The pac gene, encoding the penicillin G acylase from Escherichia coli W, is regulated by the PaaX repressor of the phenylacetate catabolic pathway. pac expression depends on the synthesis of phenylacetyl-coenzyme A. PaaX and the cyclic AMP receptor protein (CRP) bind in vitro to the Ppac promoter region. A palindromic sequence proposed as the PaaX operator is located upstream of the -35 box overlapping a CRP binding site, an unusual position that suggests a novel regulatory mechanism.

Penicillin G acylase-based stationary phases: analytical applications

A review of Penicillin G Acylase (PGA)-based stationary phases is given, focusing on immobilisation methods, selection of immobilisation material and applications in chiral liquid chromatography. Two immobilization methods, namely "in situ" and "in batch" techniques, are described for the immobilisation of PGA on silica supports. Microparticulate and monolithic silica, both functionalized with aminopropyl- and epoxy-groups, were used in the development of the PGA immobilised enzyme reactor (IMER). The best results, in terms of PGA immobilised amount and enzyme activity, were obtained with the "in situ" immobilisation on epoxy monolithic silica. The use of PGA columns as enzyme reactors for the preparation of 6-APA and for the production of enantiomeric pure drugs in a one-step reaction in described. The review also covers the application of PGA-columns as chiral stationary phases for the separation of acidic enantiomers. An on-line chromatographic system based on the PGA-IMER combined with a switching valve to an analytical column is also described as a highly efficient tool to study the enantioselective hydrolyses properties of PGA. Finally a molecular modelling study is reported with the aim to give more insights into PGA-substrates interactions and to expand the application of these stationary phases as a chiral biocatalysts for pharmaceutical processes.

Biotransformations of rifamycins: process possibilities

Rifampicin, an important antibiotic, is manufactured by chemical conversion of rifamycin S which is obtained by the chemical modification of rifamycin B. Rifamycin B is a product of Nocardia mediterranei fermentations. The chemical conversion of rifamycin B to rifamycin S has many disadvantages: Strong acidic conditions are required, heavy foam formation accompanies transformation and the yields are low. This review highlights the developments in alternative, biochemical transformations using enzymes and cells; the main focus is on transformations carried out by rifamycin oxidase.

Purification of penicillin G acylase using immobilized metal affinity membranes

The immobilized metal affinity membrane (IMAM) with modified regeneration cellulose was employed for purification of penicillin G acylase (PGA). For studying PGA adsorption capacity on the IMAM, factors such as chelator surface density, chelating metal, loading temperature, pH, NaCl concentration and elution solutions were investigated. The optimal loading conditions were found at 4 degrees C, 0.5 M NaCl, 32.04 micromol Cu(2+) per disk with 10 mM sodium phosphate buffer, pH 8.5, whereas elution conditions were: 1 M NH(4)Cl with 10 mM sodium phosphate buffer, pH 6.8. By applying these chromatographic conditions to the flow experiments in a cartridge, a 9.11-fold purification in specific activity with 90.25% recovery for PGA purification was obtained. Meanwhile, more than eight-times reusability of the membrane was achieved with the EDTA regeneration solutions.

Cloning, sequence analysis, and expression in Escherichia coli of the gene encoding an alpha-amino acid ester hydrolase from Acetobacter turbidans

The alpha-amino acid ester hydrolase from Acetobacter turbidans ATCC 9325 is capable of hydrolyzing and synthesizing beta-lactam antibiotics, such as cephalexin and ampicillin. N-terminal amino acid sequencing of the purified alpha-amino acid ester hydrolase allowed cloning and genetic characterization of the corresponding gene from an A. turbidans genomic library. The gene, designated aehA, encodes a polypeptide with a molecular weight of 72,000. Comparison of the determined N-terminal sequence and the deduced amino acid sequence indicated the presence of an N-terminal leader sequence of 40 amino acids. The aehA gene was subcloned in the pET9 expression plasmid and expressed in Escherichia coli. The recombinant protein was purified and found to be dimeric with subunits of 70 kDa. A sequence similarity search revealed 26% identity with a glutaryl 7-ACA acylase precursor from Bacillus laterosporus, but no homology was found with other known penicillin or cephalosporin acylases. There was some similarity to serine proteases, including the conservation of the active site motif, GXSYXG. Together with database searches, this suggested that the alpha-amino acid ester hydrolase is a beta-lactam antibiotic acylase that belongs to a class of hydrolases that is different from the Ntn hydrolase superfamily to which the well-characterized penicillin acylase from E. coli belongs. The alpha-amino acid ester hydrolase of A. turbidans represents a subclass of this new class of beta-lactam antibiotic acylases.

Penicillin acylase purification with the aid of pseudo-affinity chromatography

The introduction of affinity chromatography has opened a new dimension in protein purification. This article reviews the current techniques used in the penicillin acylase purification process, especially pseudo-affinity chromatography. A profile for a suitable ligand is established. An aromatic ring and the presence of one or several amino groups seem essential for proper interaction. Immobilized metal affinity chromatography now seems to be a good competitor.

Crystal structures of penicillin acylase enzyme-substrate complexes: structural insights into the catalytic mechanism

The crystal structure of penicillin G acylase from Escherichia coli has been determined to a resolution of 1.3 A from a crystal form grown in the presence of ethylene glycol. To study aspects of the substrate specificity and catalytic mechanism of this key biotechnological enzyme, mutants were made to generate inactive protein useful for producing enzyme-substrate complexes. Owing to the intimate association of enzyme activity and precursor processing in this protein family (the Ntn hydrolases), most attempts to alter active-site residues lead to processing defects. Mutation of the invariant residue Arg B263 results in the accumulation of a protein precursor form. However, the mutation of Asn B241, a residue implicated in stabilisation of the tetrahedral intermediate during catalysis, inactivates the enzyme but does not prevent autocatalytic processing or the ability to bind substrates. The crystal structure of the Asn B241 Ala oxyanion hole mutant enzyme has been determined in its native form and in complex with penicillin G and penicillin G sulphoxide. We show that Asn B241 has an important role in maintaining the active site geometry and in productive substrate binding, hence the structure of the mutant protein is a poor model for the Michaelis complex. For this reason, we subsequently solved the structure of the wild-type protein in complex with the slowly processed substrate penicillin G sulphoxide. Analysis of this structure suggests that the reaction mechanism proceeds via direct nucleophilic attack of Ser B1 on the scissile amide and not as previously proposed via a tightly H-bonded water molecule acting as a "virtual" base.

Genetic strategies to enhance penicillin acylase production in Escherichia coli

We demonstrated the improvement of penicillin acylase (PAC) production by optimization of the host/vector system using genetic engineering strategies. Several expression plasmids with improved efficiency for the transcription of the pac gene and/or translation of the pac mRNA were constructed. Mutant strains, isolated by a novel screening method, were effective for use as the expression host to produce PAC. The feasibility of using the mutant strains harboring a selection of expression plasmids for the production of PAC was evaluated. The effect of the mutation(s) resulting in the improved PAC producing ability was characterized. While the production of PAC was significantly enhanced using the optimized host/vector system, the formation of PAC inclusion bodies was shown to be another step limiting the production of recombinant PAC.

High expression of the penicillin G acylase gene (pac) from Bacillus megaterium UN1 in its own pac minus mutant

By marker exchange mutagenesis, Bacillus megaterium strain UN-1 (Bm-UN1) was used to prepare a mutant strain B. megaterium UN-cat (Bm-UNcat) lacking the penicillin G acylase gene (pac). The pac gene from Bm-UN1 was subcloned into pTF6 and the resultant plasmid, pBA402, was introduced into Bm-UNcat and Bacillus subtilis. Bm-UNcat harbouring pBA402 produced high penicillin G acylase (PAC) activity of 13.7, 19.5 and 20.4 U ml(-1) at 24, 36 and 48 h of culture, respectively. This was two- to fivefold higher than PAC produced by B. subtilis harbouring pBA402 and about 20-fold higher than PAC produced by the parent strain, Bm-UN1.

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.

Identification of the pac promoter from Kluyvera citrophila

The nucleotide sequence of the 5'-terminal region of the pac gene encoding the penicillin G acylase from Kluyvera citrophila ATCC 21285 has been determined. The transcriptional start site has been identified by primer extension analysis in a different position to that previously found for the homologous pac gene of Escherichia coli W ATCC 11105. Two nucleotide changes in the -35 box appear to be responsible of the promoter displacement in K. citrophila. A putative upstream promoter element (A+T-rich enhancer sequence) and a binding site for the cAMP receptor protein (CRP) were located upstream of the -35 box. Transcriptional lacZ and cat fusions demonstrated that pac expression was subjected to catabolite repression mediated by cAMP and its receptor protein. Remarkably, phenylacetic acid which is a potent inducer of the penicillin G acylase from E. coli, was only able to cause a significant induction of the pac expression in CRP+ cells cultured in the presence of glucose, suggesting that this effect is CRP-dependent.

Engineering antibiotic producers to overcome the limitations of classical strain improvement programs

Improvement of the antibiotic yield of industrial strains is invariably the main target of industry-oriented research. The approaches used in the past were rational selection, extensive mutagenesis, and biochemical screening. These approaches have their limitations, which are likely to be overcome by the judicious application of recombinant DNA techniques. Efficient cloning vectors and transformation systems have now become available even for antibiotic producers that were previously difficult to manipulate genetically. The genes responsible for antibiotic biosynthesis can now be easily isolated and manipulated. In the first half of this review article, the limitations of classical strain improvement programs and the development of recombinant DNA techniques for cloning and analyzing genes responsible for antibiotic biosynthesis are discussed. The second half of this article addresses some of the major achievements, including the development of genetically engineered microbes, especially with reference to beta-lactams, anthracyclines, and rifamycins.

Cloning and expression of a conjugated bile acid hydrolase gene from Lactobacillus plantarum by using a direct plate assay

The conjugated bile acid hydrolase gene from the silage isolate Lactobacillus plantarum 80 was cloned and expressed in Escherichia coli MC1061. For the screening of this hydrolase gene within the gene bank, a direct plate assay developed by Dashkevicz and Feighner (M. P. Dashkevicz and S. D. Feighner, Appl. Environ. Microbiol. 53:331-336, 1989) was adapted to the growth requirements of E. coli. Because of hydrolysis and medium acidification, hydrolase-active colonies were surrounded with big halos of precipitated, free bile acids. This phenomenon was also obtained when the gene was cloned into a multicopy shuttle vector and subsequently reintroduced into the parental Lactobacillus strain. The cbh gene and surrounding regions were characterized by nucleotide sequence analysis. The deduced amino acid sequence was shown to have 52% similarity with a penicillin V amidase from Bacillus sphaericus. Preliminary characterization of the gene product showed that it is a cholylglycine hydrolase (EC 3.5.1.24) with only slight activity against taurine conjugates. The optimum pH was between 4.7 and 5.5. Optimum temperature ranged from 30 to 45 degrees C. Southern blot analysis indicated that the cloned gene has similarity with genomic DNA of bile acid hydrolase-active Lactobacillus spp. of intestinal origin.

Enzyme reaction engineering: Synthesis of antibiotics catalysed by stabilized penicillin G acylase in the presence of organic cosolvents

By using very active and very stable penicillin G acylase (PGA)--agarose derivatives we have studied the industrial design of equilibrium-controlled synthesis of lactamic antibiotics. In the presence of high concentrations of organic cosolvents we have carried out the direct enzymatic condensation of phenylacetic acid and 6-aminopenicillanic acid to yield the model antibiotic penicillin G. We have mainly studied the integrated effect of different variables that define the reaction medium on a number of parameters of industrial interest:time course of antibiotic synthesis, highest synthetic yields, stability of the catalyst, and solubility and stability of substrates and products. The main variables tested were the nature and concentration of the organic cosolvent, pH, and temperature. The effects of the variables tested on different parameters were quite different and sometimes opposite. Hence, the optimal experimental conditions for antibiotic synthesis catalysed by PGA were established, as a compromise solution, in order to obtain good values for every parameter of industrial interest. These conditions seem to be important parameters for scale-up (e.g. we have been able to reach more than 95% of synthetic yields with productivities around 0.5 tons of model antibiotic per year per liter of catalyst).

2-Nitro-5-(6-bromohexanoylamino)benzoic acid test paper method for detecting microorganisms capable of producing cephalosporin acylases

A novel method for detecting microorganisms capable of producing cephalosporin C (CPC) acylase and/or 7-(4-carboxybutanamido)cephalosporanic acid (GL-7-ACA) acylase has been developed. The method is based on the degradation of 2-nitro-5-(6-bromohexanoylamino)benzoic acid (NBHAB), a chromogenic substrate, into yellow 2-nitro-5-aminobenzoic acid by the action of the CPC acylase or the GL-7-ACA acylase. This method is very sensitive and quite specific, and has been successfully applied to screen the acylases from a variety of bacteria. A large number of colonies isolated on a plate surface from more than 67 samples and several known bacteria were tested by the NBHAB paper. Five NBHAB-positive strains and isolates were obtained. They were further examined by the reaction of their bacterial cells upon CPC and GL-7-ACA, respectively, and by thin-layer chromatography in order to distinguish the CPC acylase from the GL-7-ACA acylase.

Expression of penicillin G acylase gene from Bacillus megaterium ATCC 14945 in Escherichia coli and Bacillus subtilis

Penicillin G acylase gene from Bacillus megaterium ATCC 14945 has been isolated. Recombinant Escherichia coli clones were screened for clear halo forming activity on the lawn of Staphylococcus aureus ATCC 6538P using the enzymatic acylating reaction of 7-aminodeacetoxycephalosporanic acid (7-ADCA) and D-(alpha)-phenylglycine methylester. The gene was contained within a 2.8 kb DNA fragment and expressed efficiently when transferred from E. coli to Bacillus subtilis. A twenty times greater amount of enzyme was produced in B. subtilis transformant than that in B. megaterium. The purified enzyme from subcloned B. subtilis showed that the native enzyme consisted of two identical subunits, each with a molecular weight of 57,000. The enzyme was able to react on various cephalosporins, i.e., cephalothin, cefamandole, cephaloridine, cephaloglycin, cephalexin and cephradine.

Purification and properties of ampicillin acylase from Pseudomonas melanogenum

Ampicillin acylase, which is known to have a novel substrate spectrum, was purified to homogeneity from Pseudomonas melanogenum by the crude extract preparation and chromatography with S-Sepharose, hydroxyapatite, CM-cellulose C-52, and CM-Sepharose. The molecular weight of the native enzyme was calculated to be 146,000 by Protein PAK-300 sw HPLC chromatography. SDS-polyacrylamide gel electrophoresis revealed that the enzyme consisted of two identical subunits with a molecular weight of 72,000. The enzyme was a glycoprotein containing 13% of total carbohydrate, and its isoelectric point was 7.2. The enzyme catalyzed both synthesis and hydrolysis of ampicillin and hydrolysis of the ester bond of phenylglycinemethylester hydrochloride substrate. The substrate specificity showed that the enzyme required a free amino group on the alpha-carbon of the acyl group. Chemical modification by diethylpyrocarbonate or N-bromosuccinimide resulted in time-dependent inactivation of the enzyme, and other results suggest the participation of essential histidine residue(s) in the catalytic activity of ampicillin acylase. Substrates of the enzyme, 6-aminopenicillanic acid and ampicillin, exhibited protective effects against N-bromosuccinimide inactivation, suggesting that the modification occurred near or at the active site.

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.

Evidence for involvement of 2 histidine residues in the reaction of ampicillin acylase

The chemical modification of purified ampicillin acylase by N-bromosuccinimide and diethylpyrocarbonate resulted in time-dependent inactivation of the enzyme. Both substrates, ampicillin and 6-aminopenicillanic acid, protected the enzyme against inactivation, suggesting that the modification occurred near or at the active site. Amino acid analyses and other data indicated that two histidyl residues per subunit molecule were essential for catalytic activity.

Expression of the Arthrobacter viscosus penicillin G acylase gene in Escherichia coli and Bacillus subtilis

The penicillin G acylase gene cloned from Arthrobacter viscosus 8895GU was subcloned into vectors, and the recombinant plasmids were transferred into Escherichia coli or Bacillus subtilis. Both E. coli and B. subtilis transformants expressed the A. viscosus penicillin G acylase. The enzyme activity was found in the intracellular portion of the E. coli transformants or in the cultured medium of the B. subtilis transformants. Penicillin G acylase production in the B. subtilis transformants was 7.2 times higher than that in the parent A. viscosus. The A. viscosus penicillin G acylase was induced by phenylacetic acid in A. viscosus, whereas the enzyme was produced constitutively in both the E. coli and B. subtilis transformants carrying the A. viscosus penicillin G acylase gene.

Molecular cloning of the penicillin G acylase gene from Arthrobacter viscosus

Penicillin G acylase was purified from the cultured filtrate of Arthrobacter viscosus 8895GU and was found to consist of two distinct subunits with apparent molecular weights of 24,000 (alpha) and 60,000 (beta). The partial N-terminal amino acid sequences of the alpha and beta subunits were determined with a protein gas phase sequencer, and a 29-base oligonucleotide corresponding to the partial amino acid sequence of the alpha subunit was synthesized. An Escherichia coli transformant having the penicillin G acylase gene was isolated from an A. viscosus gene library by hybridization with the 29-base probe. The resulting positive clone was further screened by the Serratia marcescens overlay technique. E. coli carrying a plasmid designated pHYM-1 was found to produce penicillin G acylase in the cells. This plasmid had an 8.0-kilobase pair DNA fragment inserted in the EcoRI site of pACYC184.

Two-dimensional thin-layer chromatography for simultaneous detection of bacterial beta-lactam acylases and beta-lactamases

A rapid and specific procedure was developed for the simultaneous detection of bacterial acylases and beta-lactamases, using ampicillin and cephalexin as substrates. Bacterial suspensions from agar plates were incubated separately with each beta-lactam substrate for 1 h at 37 degrees C. The supernatant of the reaction mixture was dansylated, and the dansyl derivatives were separated by two-dimensional thin-layer chromatography on polyamide sheets. The end products resulting from acylase hydrolysis, including the intact beta-lactam nucleus, 6-aminopenicillanic acid or 7-aminodeacetoxycephalosporanic acid, and the acyl side chain acid, D-(-)-alpha-aminophenylacetic acid, and the end product resulting from beta-lactamase hydrolysis (D-phenylglycylpenicilloic acid or D-phenylglycyldeacetoxycephalosporoic acid) were separated from each unhydrolyzed substrate and amino acids by this procedure. The presence of the intact beta-lactam nucleus in the reaction mixture is the indication of acylase activity. This method is sensitive and reproducible and has been successfully applied to screening for acylase activity in a variety of bacteria. It may be pharmaceutically useful for identifying organisms capable of removing the acyl side chain from naturally occurring beta-lactam antibiotics such as penicillin G, penicillin V, and cephalosporin C for production of the beta-lactam nuclei which serve as the starting materials for semisynthetic beta-lactam antibiotics.

Expression and regulation of the penicillin G acylase gene from Proteus rettgeri cloned in Escherichia coli

The penicillin G acylase genes from the Proteus rettgeri wild type and from a hyperproducing mutant which is resistant to succinate repression were cloned in Escherichia coli K-12. Expression of both wild-type and mutant P. rettgeri acylase genes in E. coli K-12 was independent of orientation in the cloning vehicle and apparently resulted from recognition in E. coli of the P. rettgeri promoter sequences. The P. rettgeri acylase was secreted into the E. coli periplasmic space and was composed of subunits electrophoretically identical to those made in P. rettgeri. Expression of these genes in E. coli K-12 was not repressed by succinate as it is in P. rettgeri. Instead, expression of the enzymes was regulated by glucose catabolite repression.