Heterologous Expression of Sfp-Type Phosphopantetheinyl Transferase is Indispensable in the Biosynthesis of Lipopeptide Biosurfactant.

Phosphopantetheinyl transferases are of tremendous enthusiasm inferable from their fundamental parts in activating polyketide, fatty acid, and non-ribosomal peptide synthetase enzymes and additionally an increasing number of biotechnological applications. The present study reports the identification of sfp gene from the Paenibacillus sp. D9, which encompasses 693 bp encoding a 230-amino acid protein with a molecular weight of 25.3 kDa. The amino acid sequence Paenibacillus sp. D9 Sfp revealed more than 90% sequence identity to other Sfp proteins from other Paenibacillus. The sfp gene was cloned and recovered efficiently using affinity chromatography with maximal specific phosphopantetheinyl transferase activity at an optimal pH of 8.0 and temperature of 30 °C. The enzyme also exhibited stability under a wide-ranging pH and temperature. The presence of Zn2+, Cu2+, and Fe2+ ions improved the enzymatic activity, while other metals such as Ni2+, Co2+, and Mg2+ had inhibitory effects. The introduction of EDTA also displayed no inhibition. Kinetic parameters were obtained having values of 4.52 mg/mL, 35.33 U/mg, 3.64 s-1, and 0.104 mM-1 s-1 for Km, Vmax, kcat, and kcat/Km, respectively. The biosurfactant synthesized by the recombinant BioSp was found to be surface active, reducing the surface tension to 33.7 mN/m on the glucose substrate after 5 days of incubation at 37 °C. The recombinant Escherichia coli strain also exhibited an improvement in biosurfactant yield (1.11 g/L) when contrasted with 0.52 g/L from Paenibacillus sp. D9. High esterase activity of 2.55 IU/mL using p-nitrophenyl acetate was observed on the recombinant strain, as the protein connected with the release of the biosurfactant was observed to be an esterase. The characteristics of improved biosurfactant and esterase synthesis by hyper-producing recombinant strain possess numerous values from biotechnology standpoint.

Chinese hamster ovary-sphingomyelin synthase2 biospecific extraction and liquid chromatography with tandem mass spectrometry analysis for the prediction of bioactive components of Rhizoma Polygoni Cuspidati.

A novel strategy for predicting bioactive components in traditional Chinese medicines using Chinese hamster ovary-sphingomyelin synthase2 (CHO-SMS2 ) cell biospecific extraction and high-performance liquid chromatography with diode array detection and tandem mass spectrometry analysis was proposed. The hypothesis is that when cells are incubated with the extract of traditional Chinese medicines, the potential bioactive components in the traditional Chinese medicines should selectively combine with the cells, while the cell-combining components would be detectable in the extract of denatured cells. The identities of the cell-combining components could be determined by liquid chromatography with tandem mass spectrometry. Using the proposed approach, the potential bioactive components of Rhizoma Polygoni Cuspidati, a commonly used traditional Chinese medicine for atherosclerosis, were detected and identified. Eight compounds in the extract of Rhizoma Polygoni Cuspidati were detected as the components selectively combined with CHO-SMS2 cells, which is a stable cell line that highly expresses sphingomyelin synthases, it was found that piceid, resveratrol, emodin-8-ß-d-glucoside, physcion-8-ß-d-glucoside, emodin, physcion, 3,5,4'-trihydroxystilbene-3-O-(6"-galloyl)-glucoside, and emodin-1-O-glucoside combined specifically with CHO-SMS2 cells. The results indicate that the proposed approach may be applied to predict the bioactive candidates in traditional Chinese medicines.

Detection of soluble co-factor dependent protein expression in vivo: application to the 4'-phosphopantetheinyl transferase PptT from Mycobacterium tuberculosis.

The need for early-on diagnostic tools to assess the folding and solubility of expressed protein constructs in vivo is of great interest when dealing with recalcitrant proteins. In this paper, we took advantage of the picomolar sensitivity of the bipartite GFP1-10/GFP11 system to investigate the solubility of the Mycobacterium tuberculosis 4'-phosphopantetheinyl transferase PptT, an enzyme essential for the viability of the tubercle bacillus. In vivo and in vitro complementation assays clearly showed the improved solubility of the full-length PptT compared to its N- and C-terminally truncated counterparts. However, initial attempts to purify the full-length enzyme overexpressed in Escherichia coli cells were hampered by aggregation issues overtime that caused the protein to precipitate within hours. The fact that the naturally occurring Coenzyme A and Mg(2+), essentials for PptT to carry out its function, could play a role in stabilizing the enzyme was confirmed using DSF experiments. In vitro activity assays were performed using the ACP substrate from the type I polyketide synthase PpsC from M. tuberculosis, a 2188 amino-acid enzyme that plays a major role in the virulence and pathogenicity of this microbial pathogen. We selected the most soluble and compact ACP fragment (2042-2188), identified by genetic selection of in-frame fragments from random library experiments, to monitor the transfer of the P-pant moiety from Coenzyme A onto a conserved serine residue of this ACP domain.

[Overexpression and purification of Escherichia coli holo-acyl carrier protein and synthesis of acyl carrier protein].

OBJECTIVE: To investigate the mechanism of fatty acids, lipid A and N-acylhomoserine lactones biosynthesis of bacteria by using high quality Escherichia coli holo-ACP and varied length chain acyl-ACPs as substrates. METHODS AND RESULTS: Using PCR technique we amplified the acpP and acpS gene fragments from genomic DNA of E. coli strain MG1655. Ligating these gene fragments with plasmids pBAD24 or pET28b respectively, we obtained 3 expression plasmids of acyl carrier protein: pBAD-ACP, pET-ACP and pET-ACP-ACPS, and one expression plasmid of holo-acyl carrier protein synthase: pBAD-ACPS. Then we constructed 3 acyl carrier protein producer strains: DH5alpha/pBAD-ACP, BL21 (DE3)/pET-ACP and BL21(DE3)/pET-ACP-ACPS by transforming E. coli strains DH5alpha or BL21(DE3)with pBAD-ACP, pET-ACP or pET-ACP-ACPS, respectively. Although these 3 strains could produce more acyl carrier protein under induction than strain DK574, which was used to purify holo-acyl carrier protein in general, the yield of holo-acyl carrier protein of these strains was still lower. In order to increase the yield of holo-acyl carrier protein in these strains, we introduced pBAD-ACPS into these strains. The assay of expressions of new strains was shown the that strain DH5alpha harbored pBAD-ACP and pBAD-ACPS double plasmids produced more holo-acyl carrier protein than strain DK574, and the purity of holo-acyl carrier protein was also increased (up to 99%). Then we purified high quality holo-acyl carrier protein from the culture of the strain DH5alpha harbored pBAD-ACP and pBAD-ACPS by using UNOsphere Q anion-exchange chromatography. Utilizing holo-acyl carrier protein and long chain fatty acids as substrates and under Vibrio harveyi acyl-acyl carrier protein synthetase catalyzing, we synthesized several different acyl-acyl carrier proteins. CONCLUSION: From this study we obtained a high holo-ACP producer strain and demonstrated that co-expressing acpP with acpS, E. coli strains could produce more holo-ACP.

Purification and characterization of the bacterial UDP-GlcNAc:undecaprenyl-phosphate GlcNAc-1-phosphate transferase WecA.

To date, the structural and functional characterization of proteins belonging to the polyprenyl-phosphate N-acetylhexosamine-1-phosphate transferase superfamily has been relentlessly held back by problems encountered with their overexpression and purification. In the present work and for the first time, the integral membrane protein WecA that catalyzes the transfer of the GlcNAc-1-phosphate moiety from UDP-GlcNAc onto the carrier lipid undecaprenyl phosphate, yielding undecaprenyl-pyrophosphoryl-GlcNAc, the lipid intermediate involved in the synthesis of various bacterial cell envelope components, was overproduced and purified to near homogeneity in milligram quantities. An enzymatic assay was developed, and the kinetic parameters of WecA as well as the effects of pH, salts, cations, detergents, and temperature on the enzyme activity were determined. A minimal length of 35 carbons was required for the lipid substrate, and tunicamycin was shown to inhibit the enzyme at submicromolar concentrations.

Biosynthesis of osmoregulated periplasmic glucans in Escherichia coli: the membrane-bound and the soluble periplasmic phosphoglycerol transferases are encoded by the same gene.

In Escherichia coli, osmoregulated periplasmic glucans (OPGs) are highly substituted by phosphoglycerol, phosphoethanolamine and succinyl residues. A two-step model was proposed to account for phosphoglycerol substitution: first, the membrane-bound phosphoglycerol transferase I transfers residues from membrane phosphatidylglycerol to nascent OPG molecules; second, the periplasmic phosphoglycerol transferase II swaps residues from one OPG molecule to another. Gene opgB was reported to encode phosphoglycerol transferase I. In this study, we demonstrate that the periplasmic enzyme II is a soluble form of the membrane-bound enzyme I. In addition, timing of OPG substitution was investigated. OPG substitution by succinyl residues occurs rapidly, probably during the backbone polymerization, whereas phosphoglycerol addition is a very progressive process. Thus, both phosphoglycerol transferase activities appear biologically necessary for complete OPG substitution.

Functional characterization and membrane topology of Escherichia coli WecA, a sugar-phosphate transferase initiating the biosynthesis of enterobacterial common antigen and O-antigen lipopolysaccharide.

WecA is an integral membrane protein that initiates the biosynthesis of enterobacterial common antigen and O-antigen lipopolysaccharide (LPS) by catalyzing the transfer of N-acetylglucosamine (GlcNAc)-1-phosphate onto undecaprenyl phosphate (Und-P) to form Und-P-P-GlcNAc. WecA belongs to a large family of eukaryotic and prokaryotic prenyl sugar transferases. Conserved aspartic acids in putative cytoplasmic loops 2 (Asp90 and Asp91) and 3 (Asp156 and Asp159) were targeted for replacement mutagenesis with either glutamic acid or asparagine. We examined the ability of each mutant protein to complement O-antigen LPS synthesis in a wecA-deficient strain and also determined the steady-state kinetic parameters of the mutant proteins in an in vitro transfer assay. Apparent K(m) and V(max) values for UDP-GlcNAc, Mg(2+), and Mn(2+) suggest that Asp156 is required for catalysis, while Asp91 appears to interact preferentially with Mg(2+), possibly playing a role in orienting the substrates. Topological analysis using the substituted cysteine accessibility method demonstrated the cytosolic location of Asp90, Asp91, and Asp156 and provided a more refined overall topological map of WecA. Also, we show that cells expressing a WecA derivative C terminally fused with the green fluorescent protein exhibited a punctate distribution of fluorescence on the bacterial surface, suggesting that WecA localizes to discrete regions in the bacterial plasma membrane.

Identification and characterization of human cardiolipin synthase.

The mitochondrial phospholipid cardiolipin is synthesized from cytidinediphosphate-diacylglycerol and phosphatidylglycerol, a process catalyzed by the enzyme cardiolipin synthase. In this study, we identified a human candidate gene/cDNA for cardiolipin synthase, C20orf155. Expression of this candidate cDNA in the (cardiolipin synthase-deficient) crd1Delta yeast confirmed that it indeed encodes human cardiolipin synthase. Purified mitochondria of the crd1Delta expressing human cardiolipin synthase were used to characterize the enzyme. It has an alkaline pH optimum, requires divalent cations for activity and appears to have a different substrate preference for cytidinediphosphate-diacylglycerol species when compared to phosphatidylglycerol species. The possible implications for CL synthesis and remodeling are discussed.

Gene cloning, expression and functional characterization of a phosphopantetheinyl transferase from Vibrio anguillarum serotype O1.

Phosphopantetheinyl transferases (PPTases) catalyze the essential post-translational activation of carrier proteins from fatty acid synthetases (FASs) in primary metabolism and polyketide synthetases (PKSs) and non-ribosomal polypeptide synthetases (NRPSs) in secondary metabolism. Bacteria typically harbor one PPTase specific for carrier proteins of primary metabolism (ACPS-type PPTases) and at least one capable of modifying carrier proteins involved in secondary metabolism (Sfp-type PPTases). Anguibactin, an important virulent factor in Vibrio anguillarum serotype O1, has been reported to be synthesized by a nonribosomal peptide synthetases (NRPS) system encoded on a 65-kb virulent plasmid pJM1 from strain 775 of V. anguillarum serotype O1, and the PPTase, necessary for the activation of the anguibactin-NRPS, is therefore expected to lie on the pJM1 plasmid. In this work, a putative PPTase gene, angD, was first identified on pEIB1 plasmid (a pJM1-like plasmid) from a virulent strain MVM425 of V. anguillarum serotype O1. A recombinant clone carrying complete angD was able to complement an Escherichia coli entD mutant deficient in Sfp-type PPTase. angD was overexpressed in E. coli and the resultant protein, AngD, was purified. Simultaneously, two carrier proteins involved in anguibactin-NRPS, ArCP and PCP, were overproduced in E. coli and purified. The purified AngD, PCP and ArCP were used to establish an in vitro enzyme reaction, and the PPTase activity of AngD was proved through HPLC analysis to detect the conversion of inactive carrier proteins to active carrier proteins in the reaction mixture. Co-expression of AngD with PCP or ArCP showed that AngD functioned well as a PPTase in vivo in E. coli, modifying PCP and ArCP completely.

Purification, characterization, and identification of a sphingomyelin synthase from Pseudomonas aeruginosa. PlcH is a multifunctional enzyme.

Sphingomyelin synthase is the enzyme that synthesizes sphingomyelin (SM) in mammalian cells by transferring a phosphorylcholine moiety from phosphatidylcholine to ceramide. Despite its importance, the gene and/or the protein responsible for this activity has not yet been identified. Here we report the purification, identification, and biochemical characterization of an enzymatic activity that synthesizes SM in Pseudomonas aeruginosa. SM synthase-like activity was found secreted in the culture medium of P. aeruginosa, strains PA01 and PAK, whereas it could not be detected in cultures of Escherichia coli. From the medium of PAK cultures, SM synthase was purified through sequential chromatographic columns. After separation on polyacrylamide-SDS gels and visualization by silver staining, the purified enzyme showed two bands, one of approximately 75 kDa and one of 30-35 kDa. Interestingly, the highly purified SM synthase preparation also showed neutral sphingomyelinase activity. We therefore investigated whether the protein we purified as SM synthase could actually be the previously identified PlcH, a 78-kDa phospholipase C known to hydrolyze phosphatidylcholine and SM in P. aeruginosa. First, the purified SM synthase preparation contained a 78-kDa protein that reacted with monoclonal antibodies raised against purified PlcH. Second, purified PlcH showed SM synthase activity. Third, using different knockout mutant strains for the PlcH operon, PlcH was found to be necessary for SM synthase activity in P. aeruginosa. Interestingly, SM synthase activity was specific to the Pseudomonas PlcH as other bacterial phospholipases did not display SM synthase activity. Biochemical studies on the Pseudomonas SM synthase confirmed that it is a transferase, similar to the mammalian enzyme, that specifically recognizes the choline head-group and the primary hydroxyl on ceramide. This SM synthase did not have reverse transferase activity. In conclusion, the Pseudomonas PlcH also exerts SM synthase activity; therefore, for the first time, we have identified a structural gene for a SM synthase.

Purified, recombinant TagF protein from Bacillus subtilis 168 catalyzes the polymerization of glycerol phosphate onto a membrane acceptor in vitro.

We report the first characterization of a recombinant protein involved in the polymerization of wall teichoic acid. Previously, a study of the teichoic acid polymerase activity associated with membranes from Bacillus subtilis 168 strains bearing thermosensitive mutations in tagB, tagD, and tagF implicated TagF as the poly(glycerol phosphate) polymerase (Pooley, H. M., Abellan, F. X., and Karamata, D. (1992) J. Bacteriol. 174, 646-649). In the work reported here, we have demonstrated an unequivocal role for tagF in the thermosensitivity of one such mutant (tagF1) by conditional complementation at the restrictive temperature with tagF under control of the xylose promoter at the amyE locus. We have overexpressed and purified recombinant B. subtilis TagF protein, and we provide direct biochemical evidence that this enzyme is responsible for polymerization of poly(glycerol phosphate) teichoic acid in B. subtilis 168. Recombinant hexahistidine-tagged TagF protein was purified from Escherichia coli and was used to develop a novel membrane pelleting assay to monitor poly(glycerol phosphate) polymerase activity. Purified TagF was shown to incorporate radioactivity from its substrate CDP-[(14)C]glycerol into a membrane fraction in vitro. This activity showed a saturable dependence on the concentration of CDP-glycerol (K(m) of 340 microm) and the membrane acceptor (half-maximal activity at 650 microg of protein/ml of purified B. subtilis membranes). High pressure liquid chromatography analysis confirmed the polymeric nature of the reaction product, approximately 35 glycerol phosphate units in length.

Expression, purification, crystallization and preliminary X-ray analysis of the acyl carrier protein synthase (acpS) from Mycobacterium tuberculosis.

Acyl carrier protein synthase (acpS) catalyzes the formation of holo-ACP, which mediates the transfer of acyl fatty-acid intermediates during the biosynthesis of fatty acids and lipids. An expression and purification system for the Mycobacterium tuberculosis (Mtb) acpS has been established that yields approximately 15 mg l(-1) of the enzyme in soluble form. The purified enzyme has been crystallized by the vapour-diffusion method using 2-propanol as a precipitant. The original crystal size has been improved significantly by the addition of glycerol to the mother liquor. Mtb acpS crystals belong to the space group R3, with unit-cell parameters a = b = 68.53, c = 85.9 A. Native data have been collected under cryogenic conditions; phase resolution by molecular replacement and selenomethionine-aided multi-wavelength anomalous dispersion techniques is ongoing.

Purification of phosphatidylglycerophosphate synthase from Chinese hamster ovary cells.

Phosphatidylglycerophosphate (PGP) synthase catalyses the committed step in the biosynthesis of phosphatidylglycerol and cardiolipin in mammalian cells. Recently we isolated a Chinese hamster ovary (CHO) PGS1 cDNA encoding PGP synthase. In the present study we purified this PGP synthase to near-homogeneity from the mitochondrial fraction of CHO-K1 cells; the final enzyme preparation gave a single 60 kDa protein on SDS/PAGE. Polyclonal antibodies raised against a recombinant CHO PGS1 protein cross-reacted with the purified 60 kDa protein and with CHO membrane proteins of 60 kDa and 62 kDa that increased after transfection with the PGS1 cDNA. The 60 and 62 kDa protein levels in a PGP synthase-defective mutant of CHO-K1 cells were markedly lower than those in CHO-K1 cells. These results indicated that the purified 60 kDa protein was PGP synthase encoded by the PGS1 gene. In addition we found that the purified PGP synthase had no PGP phosphatase activity, indicating that phosphatidylglycerol was produced from CDP-diacylglycerol through two steps catalysed by distinct enzymes, PGP synthase and PGP phosphatase.

Overexpression and purification of the Escherichia coli inner membrane enzyme acyl-acyl carrier protein synthase in an active form.

Acyl-acyl carrier protein synthase (Aas) is widely used to synthesize thioester adducts of fatty acids between 8 and 18 carbons in length enzymatically to the phosphopantetheine group of acyl carrier protein. The enzyme is an 80.6-kDa inner membrane protein that functions in vivo as a 2-acylglycerophosphoethanolamine acyltransferase. The E. coli aas open reading frame was inserted into the expression plasmid pET28a so that, upon expression, a 21-amino-acid extension containing 6 consecutive histidine residues was added to the carboxyl terminus. The plasmid was designated pAasH. The activity of Aas in membranes was assessed from several cell lines. Membranes from the commonly used host line BL21(DE3) containing pAasH accumulated 30-fold and 38-fold more Aas activity than membranes from BL21(DE3) cells lacking the plasmid, when induced with isopropyl beta-d-thiogalactopyranoside (IPTG) or lactose, respectively. When pAasH was expressed under IPTG induction in cell line C41(DE3), a previously described cell line selected to enhance the expression of membrane proteins, Aas levels accumulated to 135-fold higher levels than in the cell line lacking the plasmid. Functional Aas can be isolated from either BL21(DE3) or C41(DE3) cell lines by differential centrifugation, followed by detergent extraction with Triton X-100 and nickel nitrilotriacetic acid affinity chromatography. The overexpression of Aas in cell line C41(DE3) is noteworthy compared to cell line BL21(DE3) because it results in a 3- to 4-fold higher accumulation of active enzyme in the membrane fraction and a lower proportion of inactive protein in the inclusion body.

Crystallization and preliminary crystallographic studies of Sfp: a phosphopantetheinyl transferase of modular peptide synthetases.

The Bacillus subtilis Sfp protein is required for the non-ribosomal biosynthesis of the lipoheptapeptide antibiotic surfactin. It converts seven peptidyl carrier protein (PCP) domains of the surfactin synthetase SfrA-(A-C) to their active holo-forms by 4'-phosphopantetheinylation. The B. subtilis sfp gene was overexpressed in Escherichia coli and its gene product was purified to homogeneity and crystallized. Well diffracting single crystals were obtained from Sfp as well as from a selenomethionyl derivative, using sodium formate as a precipitant. The crystals belong to the tetragonal space group P41212/P43212, with unit-cell parameters a = b = 65.3, c = 150.5 A. They diffract beyond 2.8 A and contain one molecule in the asymmetric unit.

Characterization of a novel GDP-mannose:Serine-protein mannose-1-phosphotransferase from Leishmania mexicana.

Protozoan parasites of the genus Leishmania secrete a number of glycoproteins and mucin-like proteoglycans that appear to be important parasite virulence factors. We have previously proposed that the polypeptide backbones of these molecules are extensively modified with a complex array of phosphoglycan chains that are linked to Ser/Thr-rich domains via a common Manalpha1-PO4-Ser linkage (Ilg, T., Overath, P., Ferguson, M. A. J., Rutherford, T., Campbell, D. G., and McConville, M. J. (1994) J. Biol. Chem. 269, 24073-24081). In this study, we show that Leishmania mexicana promastigotes contain a peptide-specific mannose-1-phosphotransferase (pep-MPT) activity that adds Manalpha1-P to serine residues in a range of defined peptides. The presence and location of the Manalpha1-PO4-Ser linkage in these peptides were determined by electrospray ionization mass spectrometry and chemical and enzymatic treatments. The pep-MPT activity was solubilized in non-ionic detergents, was dependent on Mn2+, utilized GDP-Man as the mannose donor, and was expressed in all developmental stages of the parasite. The pep-MPT activity was maximal against peptides containing Ser/Thr-rich domains of the endogenous acceptors and, based on competition assays with oligosaccharide acceptors, was distinct from other leishmanial MPTs involved in the initiation and elongation of lipid-linked phosphoglycan chains. In subcellular fractionation experiments, pep-MPT was resolved from the endoplasmic reticulum marker BiP, but had an overlapping distribution with the cis-Golgi marker Rab1. Although Man-PO4 residues in the mature secreted glycoproteins are extensively modified with mannose oligosaccharides and phosphoglycan chains, similar modifications were not added to peptide-linked Man-PO4 residues in the in vitro assays. Similarly, Man-PO4 residues on endogenous polypeptide acceptors were also poorly extended, although the elongating enzymes were still active, suggesting that the pep-MPT activity and elongating enzymes may be present in separate subcellular compartments.

Purification and characterization of phosphatidylglycerolphosphate synthase from Schizosaccharomyces pombe.

The enzyme CDP-diacylglycerol:sn-glycerol-3-phosphate 3-phosphatidyltransferase (phosphatidylglycerolphosphate synthase; PGPS4; EC 2.7.8.5) is located in the mitochondrial inner membrane and catalyzes the committed step in the cardiolipin branch of phospholipid synthesis. Previous studies revealed that PGPS is the most highly regulated enzyme in cardiolipin biosynthesis in both Saccharomyces cerevisiae and Schizosaccharomyces pombe. In this work, we report the purification to homogeneity of PGPS from S. pombe. The enzyme was solubilized from the mitochondrial membrane of S. pombe with Triton X-100. The solubilized enzyme, together with the associated detergent and intrinsic lipids, had a molecular mass of 120 kDa, as determined by gel filtration. The enzyme was further purified using salt-induced phase separation, gel filtration, and ionic exchange, hydroxylapatite, and affinity chromatographies. The procedure yielded a homogeneous protein preparation, evidenced by both SDS-polyacrylamide gel electrophoresis (PAGE) and agarose isoelectric focusing under nondenaturing conditions. The purified enzyme had an apparent molecular mass of 60 kDa as determined by SDS-PAGE. The enzyme showed a strong dependence on lipid cofactors for activity in vitro. While both phosphatidic acid and CDP-diacylglycerol appeared to be activators, the most significant activation was observed with cardiolipin. The possible physiological significance of the lipid cofactor effect is discussed. This is the first purification of a eucaryotic PGPS enzyme to date, and the first purification of a phospholipid biosynthetic enzyme from S. pombe.

Identification, isolation and biochemical characterization of a phosphopantetheine:protein transferase that activates the two type-I fatty acid synthases of Brevibacterium ammoniagenes.

Upon heterologous expression of the Brevibacterium ammoniagenes type-I fatty acid synthase FAS-A in Escherichia coli, only the pantetheine-free apoenzyme is synthesized. Activation of FAS-A to its holoform was achieved by transformation with a second B. ammoniagenes gene, PPT1, encoding a type-I FAS-specific phosphopantetheine transferase. PPT1 was identified as a coding sequence located immediately downstream of the second FAS gene present on the B. ammoniagenes genome, fasB. Due to this linkage, PPT1 was part of the cloned fasB DNA region and, consequently, FAS-B but not FAS-A was synthesized as holoFAS in E. coli. PPT1 encodes a protein of 153 amino acids and has a calculated molecular mass of 16,884 Da. The PPT1 gene product contains 25% identical and 42% conserved amino acids compared with the type-II acyl-carrier-protein-activating enzyme of E. coli. Although there is essentially no intergenic region between fasB and PPT1, the PPTase gene is autonomously expressed in E. coli if flanked by 200 bp of its endogenous 5' DNA. The structural independence of Ppt1p was confirmed immunologically, as specific antibodies react with the purified PPTase but not with FAS-B. Overexpression and purification of the His-tagged Ppt1p allowed the in vitro activation of apoFAS-A. This holoenzyme synthesis requires, in addition to Ppt1p, CoA and Mg2+ and leads to a specific FAS activity comparable to that of natural B. ammoniagenes FAS-A. The reactivity of the in vitro-activated FAS-A was verified by the optical FAS assay and by analysis of its in vitro products. In agreement with the known overall colinearity of B. ammoniagenes FAS-B and the Saccharomyces cerevisiae FAS1 and FAS2 gene products, a PPT1-like sequence is also observed at the C terminus of FAS2. However, in contrast to B. ammoniagenes PPT1, this sequence is an integral part of the yeast FAS2 gene. Thus, activation of type-I fatty acid synthases may be accomplished by distinct trans-acting PPTase enzymes and by intrinsic cis-acting PPTase domains.

Cardiolipin synthase from mammalian mitochondria.

Cardiolipin was first isolated from beef heart and was shown to contain an unusually high content of linoleic acid ester residues. Cardiolipin is found throughout the eukaryotes including animals, plants and fungi. In mammalian tissue and in yeast, cardiolipin is found exclusively in mitochondria. Mitochondrial synthesis of cardiolipin utilizes phosphatidylglycerol and CDP-diacylglycerol as substrates in a reaction which requires a divalent cation (Mg2+, Mn2+ or Co2+). Cardiolipin synthase has been purified to near-homogeneity from rat liver by solubilization with Zwittergent 3-14 followed by FPLC anion exchange, gel permeation and chromatofocusing steps. Cardiolipin synthase has a molecular mass of 50 kDa, a pH optimum of 8.0, and requires added phospholipids (phosphatidylethanolamine and cardiolipin) and 4 mM Co2+ for optimal activity. Except for the effects of divalent cations and the requirement for phospholipids, little is known about the regulation of cardiolipin synthase. Cardiolipin deficiency in aging mitochondria has been linked to decreased metabolite transport across the inner membrane. Both cardiolipin levels and cardiolipin synthase activity are increased in hyperthyroidism and decreased in hypothyroidism suggesting regulation by thyroid hormone. Mammalian cardiolipin synthase has not been sequenced or cloned and its biological role in mitochondria is not yet fully understood.