Cloning and characterization of penicillin V acylase from Streptomyces mobaraensis

We report on the molecular cloning and characterization of penicillin V acylase (PVA) from an actinomycete, Streptomyces mobaraensis (Sm-PVA), which was originally isolated as an acylase that efficiently hydrolyzes the amide bond of various N-fatty-acyl-l-amino acids and N-fatty-acyl-peptides as well as capsaicin (8-methyl-N-vanillyl-6-nonenamide). In addition, the purified Sm-PVA hydrolyzed penicillin V with the highest activity (k(cat)) among the PVAs so far reported, penicillin G, and 2-nitro-5-phenoxyacetamide benzoic acid. The BLAST search revealed that the Sm-PVA precursor is composed of a polypeptide that is characteristic of enzymes belonging to the beta-lactam acylase family with four distinct segments; a signal sequence (43 amino acids), an alpha subunit (173 amino acids), a linker peptide (28 amino acids), and a beta subunit (570 amino acids). The mature, active Sm-PVA is a heterodimeric protein with alpha and beta subunits, in contrast to PVAs isolated from Bacillus sphaericus and B. subtilis, which have a homotetrameric structure. The amino acid sequence of Sm-PVA showed identities to PVA from S. lavendulae, N-acylhomoserine lactone-degrading acylase from Streptomyces sp., cyclic lipopeptide acylase from Streptomyces sp., and aculeacin A acylase from Actinoplanes utahensis with 68, 67, 67, and 41% identities, respectively.     

Penicillin production by glucose-derepressed mutants ofPenicillium chrysogenum

Summary Wild-type strains ofPenicillium chrysogenum produce lower penicillin V titers in media containing excess glucose. Two mutant strains were isolated and shown to produce normal penicillin V titers in the presence of excess glucose. These strains, designated as glucose-repression insensitive (GRI) mutants, produced higher penicillin V titers than the wild-type strain in media containing lactose as the main carbohydrate source. In lactose-based media, the production of penicillin V was depressed to a much lesser extent by in-cycle additions of glucose with the GRI mutants when compared to the wild-type strain. In short-term biosynthesis experiments using washed cells in a medium containing glucose as the sole carbon source, the GRI mutants produced penicillin V at a faster rate than the wild-type strain. In fed-batch fermentations in 14-liter fermentors, where glucose was fed continuously and pH controlled, both GRI mutants produced more than 10% higher penicillin V titers than the wild-type strain. These results suggest that isolation of GRI mutants is an effective way to select for higher producing strains and that the synthesis of penicillin synthesizing enzymes in GRI mutants may be less repressed by glucose than in wild-type strains.     

Analysis of a gene (vch) encoding hemolysin isolated and sequenced from Vibrio campbellii

This study describes the amplification, localization, and sequence analysis of a hemolysin gene from type strain V. campbellii NBRC 15631--the first report of a full-length hemolysin gene for the species. An amplicon ( approximately 600 bp) of polymerase chain reaction performed using V. campbellii DNA template and primers previously designed to target a fragment of V. harveyi hemolysin gene (vhh) was shotgun-cloned and sequenced, generating 576 bp nucleotide sequences of the V. campbellii hemolysin gene. PCR primers designed based on these initial sequences were used to amplify a 551-bp V. campbellii hemolysin gene fragment that was used as probe in Southern hybridization, which localized the complete hemolysin gene within a 3.5-kb HindIII restriction fragment of the V. campbellii genomic DNA. To obtain the remaining DNA sequences upstream and downstream of the 576-bp hemolysin gene sequences, inverse PCR was performed using a self-ligated (circularized) V. campbellii HindIII restriction fragment as the template and PCR primers designed to amplify flanking regions of the 576-bp gene fragment. Nucleotide sequences from the terminal regions of the 3.1-kb product of inverse PCR provided the flanking sequences, resulting in the complete sequence for the V. campbellii hemolysin gene. A VCH PCR primer set was designed to amplify a 1.3-kb region containing the entire hemolysin gene even from other V. campbellii strains, which was sequenced to confirm the V. campbellii hemolysin gene sequence. An open reading frame (ORF) of 1,254 bp (designated as vch) was identified, sharing 79% sequence identity with V. harveyi hemolysin gene vhh, representing 262 base substitutions between V. campbellii and V. harveyi. The deduced amino acid sequence of V. campbellii hemolysin (VCH) shows homologies to the V. harveyi hemolysin (VHH), thermolabile hemolysin of V. parahaemolyticus, proteins such as phospholipase of V. vulnificus and lecithinases of V. mimicus and V. cholerae. The VCH primer set did not produce any amplicon in PCR using V. harveyi DNA, and may therefore be used to distinguish environmental strains of V. campbellii from V. harveyi.     

Purification and characterization of YxeI, a penicillin acylase from Bacillus subtilis

The paper reports the purification and characterization of the first penicillin acylase from Bacillus subtilis. YxeI, the protein annotated as hypothetical, coded by the gene yxeI in the open reading frame between iol and hut operons in B. subtilis was cloned and expressed in Eshcherichia coli, purified and characterized. The purified protein showed measurable penicillin acylase activity with penicillin V. The enzyme was a homotetramer of 148 kDa. The apparent K_m of the enzyme for penicillin V and the synthetic substrate 2-nitro-5-(phenoxyacetamido)-benzoic acid was 40 mM and 0.63 mM, respectively, and the association constants were 8.93 × 10² M⁻¹ and 2.51 × 10⁵ M⁻¹, respectively. It was inhibited by cephalosporins and conjugated bile salts, substrates of the closely related bile acid hydrolases. It had good sequence homology with other penicillin V acylases and conjugated bile acid hydrolases, members of the Ntn hydrolase family. The N-terminal nucleophile was a cysteine which is revealed by a simple removal of N-formyl-methionine. The activity of the protein was affected by high temperature, acidic pH and the presence of the denaturant guanidine hydrochloride.     

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.     

Inhibition of acid production in Streptococcus mutans R9: Inhibition constants and reversibility

Abstract The pac gene encoding the penicillin G acylase (PGA) of Bacillus megaterium ATCC 14945 has been cloned in Escherichia coli HB101 ( proA, leuB ) using a selective minimal medium containing phenylacetyl-L-leucine instead of L-leucine. The nucleotide sequence of this gene has been determined and contains an open reading frame of 2406 nucleotides. The deduced amino acid sequence shows significant similarity with other β-lactam acylases. Although the PGA of B. megaterium is extracellular, the enzyme produced in E. coli appears to have a cytoplasmic localization.     

Decreased production ofpara-hydroxypenicillin V in penicillin V fermentations

Summary Penicillin V (phenoxymethyl penicillin) is produced by industrial strains ofPenicillium chrysogenum in the presence of phenoxyacetic acid (POAc), a side-chain precursor for the penicillin V molecule. The wild-type strain ofP. chrysogenum produces an undesirable penicillin byproduct,para-hydroxypenicillin V (p-OH penicillin V), in addition to penicillin V, viapara-hydroxylation of POAc and subsequent incorporation of thep-OH phenoxyacetic acid into the penicillin molecule. Most of thep-OH penicillin V is produced late in cycle when the POAc concentration in the medium is nearly depleted. The level ofp-OH penicillin V produced by the control strain ranges up to 10–15% of the total penicillins produced. 3-Phenoxypropionic acid andp-bromophenylacetic acid partially inhibit the formation ofp-OH penicillin V with a minimal effect on penicillin V productivity. Mutants deficient in their ability to hydroxylate POAc were found to produce lower levels ofp-OH penicillin V. Multi-step mutation and screening, starting with the wild-type strain, have culminated in isolation of mutants which producep-OH penicillin V as 1% of the total penicillins with no adverse effect on penicillin V productivity.     

产黄青霉谷胱甘肽S-转移酶基因PcgstA的克隆与鉴定

从青霉素工业生产菌产黄青霉(Penicilliumchrysogenum)中首次克隆了一个谷胱甘肽S-转移酶(GST)基因,定名为PcgstA.该基因的开放阅读框长840bp,含有两个内含子,编码一个238氨基酸残基的蛋白质.其推断的氨基酸序列与一些已经鉴定的丝状真菌GST具有50%左右的序列一致性.PcgstA的完整编码区经RT-PCR扩增、验证,插入原核表达载体pET11a,转化大肠杆菌BL21(DE3)-RP菌株,表达得到重组PcGSTA蛋白.酶活测定证实,重组PcGSTA具有GST活性,其对底物CDNB(1-chloro-2,4-dinitrobenzene)的比活为(0.159±0.031)μmol/(min·mg).利用TaqMan探针法,对PcgstA的表达情况进行了比较.结果表明,在添加了侧链前体苯乙酸的青霉素生产培养基中,PcgstA的表达水平和在不含苯乙酸培养基中的表达相比明显下调,显示了该基因与苯乙酸代谢的关系.     

In vitro binding of the bacteriophage f1 gene V protein to the gene II RNA-operator and its DNA analog.

We have investigated the binding of the f1 single-stranded DNA-binding protein (gene V protein) to DNA oligonucleotides and RNA synthesized in vitro. The first 16 nucleotides of the f1 gene II mRNA leader sequence were previously identified as the gene II RNA-operator; the target to which the gene V protein binds to repress gene II translation. Using a gel retardation assay, we find that the preferential binding of gene V protein to an RNA carrying the gene II RNA-operator sequence is affected by mutations which abolish gene II translational repression in vivo. In vitro, gene V protein also binds preferentially to a DNA oligonucleotide whose sequence is the DNA analog of the wild-type gene II RNA-operator. Therefore, the gene V protein recognizes the gene II mRNA operator sequence when present in either an RNA or DNA context.     

Characterization of a phenylacetate-CoA ligase from Penicillium chrysogenum

Enzymatic activation of PAA (phenylacetic acid) to phenylacetyl-CoA is an important step in the biosynthesis of the beta-lactam antibiotic penicillin G by the fungus Penicillium chrysogenum. CoA esters of PAA and POA (phenoxyacetic acid) act as acyl donors in the exchange of the aminoadipyl side chain of isopenicillin N to produce penicillin G or penicillin V. The phl gene, encoding a PCL (phenylacetate-CoA ligase), was cloned in Escherichia coli as a maltose-binding protein fusion and the biochemical properties of the enzyme were characterized. The recombinant fusion protein converted PAA into phenylacetyl-CoA in an ATP- and magnesium-dependent reaction. PCL could also activate POA, but the catalytic efficiency of the enzyme was rather low with k(cat)/K(m) values of 0.23+/-0.06 and 7.8+/-1.2 mM(-1).s(-1) for PAA and POA respectively. Surprisingly, PCL was very efficient in catalysing the conversion of trans-cinnamic acids to the corresponding CoA thioesters [k(cat)/K(m)=(3.1+/-0.4)x10(2) mM(-1).s(-1) for trans-cinnamic acid]. Of all the substrates screened, medium-chain fatty acids, which also occur as the side chains of the natural penicillins F, DF, H and K, were the best substrates for PCL. The high preference for fatty acids could be explained by a homology model of PCL that was constructed on the basis of sequence similarity with the Japanese firefly luciferase. The results suggest that PCL has evolved from a fatty-acid-activating ancestral enzyme that may have been involved in the beta-oxidation of fatty acids.     

Analysis of gyrB and toxR gene sequences of Vibrio hollisae and development of gyrB- and toxR-targeted PCR methods for isolation of V. hollisae from the environment and its identification

Isolation of Vibrio hollisae strains, particularly from the environment, is rare. This may be due, in part, to the difficulty encountered when using conventional biochemical tests to identify the microorganism. In this study, we evaluated whether two particular genes may be useful for the identification of V. hollisae. The two genes are presumed to be conserved among the bacterial species (gyrB) or among the species of the genus Vibrio (toxR). A portion of the gyrB sequence of V. hollisae was cloned by PCR using a set of degenerate primers. The sequence showed 80% identity with the corresponding Vibrio parahaemolyticus gyrB sequence. The toxR gene of V. hollisae was cloned utilizing a htpG gene probe derived from the V. parahaemolyticus htpG gene, which is known to be linked to the toxR gene in V. hollisae. The coding sequence of the cloned V. hollisae toxR gene had 59% identity with the V. parahaemolyticus toxR coding sequence. The results of DNA colony hybridization tests using the DNA probes derived from the two genes of V. hollisae indicated that these gene sequences could be utilized for differentiation of V. hollisae from other Vibrio species and from microorganisms found in marine fish. PCR methods targeting the two gene sequences were established. Both PCR methods were shown to specifically detect the respective target sequences of V. hollisae but not other organisms. A strain of V. hollisae added at a concentration of 1 to 10(2) CFU/ml to alkaline peptone water containing a seafood sample could be detected by a 4-h enrichment incubation in alkaline peptone water at 37 degrees C followed by quick DNA extraction with an extraction kit and 35-cycle PCR specific for the V. hollisae toxR gene. We conclude that screening of seafood samples by this 35-cycle, V. hollisae toxR-specific PCR, followed by isolation on a differential medium and identification by the above htpG- and toxR-targeted PCR methods, can be useful for isolation from the environment and identification of V. hollisae.     

Characterization of a Bifidobacterium longum BORI dipeptidase belonging to the U34 family

A dipeptidase was purified from a cell extract of Bifidobacterium longum BORI by ammonium sulfate precipitation and chromatography on DEAE-cellulose and Q-Sepharose columns. The purified dipeptidase had a molecular mass of about 49 kDa and was optimally active at pH 8.0 and 50 degrees C. The enzyme was a strict dipeptidase, being capable of hydrolyzing a range of dipeptides but not tri- and tetrapeptides, p-nitroanilide derivatives of amino acids, or N- or C-terminus-blocked dipeptides. A search of the amino acid sequence of an internal tryptic fragment against protein sequences deduced from the total genome sequence of B. longum NCC2705 revealed that it was identical to an internal sequence of the dipeptidase gene (pepD), which comprised 1,602 nucleotides encoding 533 amino acids with a molecular mass of 60 kDa, and thereby differed considerably from the 49-kDa mass of the purified dipeptidase. To understand this discrepancy, pepD was cloned into an Escherichia coli expression vector (pBAD-TOPO derivative) to generate the recombinant plasmids pBAD-pepD and pBAD-pepD-His (note that His in the plasmid designation stands for a polyhistidine coding region). Both plasmids were successfully expressed in E. coli, and the recombinant protein PepD-His was purified using nickel-chelating affinity chromatography and reconfirmed by internal amino acid sequencing. The PepD sequence was highly homologous to those of the U34 family of peptidases, suggesting that the B. longum BORI dipeptidase is a type of cysteine-type N-terminal nucleophile hydrolase and has a beta-hairpin motif similar to that of penicillin V acylase, which is activated by autoproteolytic processing.     

A gene for the enterotoxin zonula occludens toxin is present in Vibrio mimicus and Vibrio cholerae O139

Abstract The presence of the zonula occludens toxin (ZOT) gene, which encodes an enterotoxin produced by serotype O1 strains of the pathogenic bacterium, Vibrio cholerae , in addition to cholera toxin, was investigated in selected strains of V. mimicus and the new pandemic V. cholerae non-O1 serotype O139. The zot gene was detected by polymerase chain reaction (PCR) amplification, using sets of primers based on the sequence of the V. cholerae O1 zot sequence. PCR amplification of genomic DNAs of both cholera toxin gene ( ctx ) positive and ctx⁻ strains of V. mimicus detected the presence of zot gene. An Acc -I- Eco RV V. cholerae zot gene fragment designed to overlap PCR products was used as a probe. Southern hybridization studies confirmed that the PCR fragments from V. mimicus and V. cholerae O139 were strongly homologous to the V. cholerae O1 zot gene. The zot gene was found with 3 to 5 strains of V. mimicus of which only one strain harbored the ctx gene. The presence of a zot gene in ctx⁻ toxigenic V. mimicus indicates a possible role of ZOT in the toxigenicity of this species. We conclude that, in addition to ctx, V. mimicus and V. cholerae O139 have the potential to produce ZOT.     

Molecular cloning of Bacillus sphaericus penicillin V amidase gene and its expression in Escherichia coli and Bacillus subtilis

The Bacillus sphaericus gene coding for penicillin V amidase, which catalyzes the hydrolysis of penicillin V to yield 6-aminopenicillanic acid and phenoxyacetic acid, has been isolated by molecular cloning in Escherichia coli. The gene is contained within a 2.2-kilobase HindIII-PstI fragment and is expressed when transferred into E. coli and Bacillus subtilis. The expression in B. subtilis carrying the recombinant plasmid is approximately two times higher than in the original B. sphaericus strain. A comparison of the purified enzyme from B. sphaericus and the expressed gene product in E. coli minicells suggests that the native enzyme consists of four identical subunits, each with a molecular weight of 35,000.