Acyl carrier protein of Azospirillum brasilense: properties of the purified protein and sequencing of the corresponding gene, acpP

Acyl carrier protein (ACP) plays a crucial role in bacterial fatty acid synthesis. Cloning genes encoding ACPs from Gram-negative bacteria in Escherichia coli is difficult due to adverse effects of the cloned gene on host cell viability, and we were unsuccessful in cloning the full length ACP gene (acpP) from Azospirillum brasilense using conventional methods. Therefore, ACP from A. brasilense was purified to homogeneity and a part of the acpP gene was cloned using the polymerase chain reaction (PCR) technique with two primers, one designed from the N-terminal amino acid sequence of the purified ACP and the other from the highly conserved amino acid sequence of bacterial ACPs. The nucleotide sequence of the gene was obtained by cloning and sequencing inverse PCR products containing the acpP region generated by two oppositely oriented internal primers designed from the partial acpP gene sequence using restriction-enzyme-digested, self-circularized chromosomal DNA fragments as templates. Characterization of the purified ACP and analysis of the derived amino acid sequence of the acpP gene of A. brasilense revealed that: (a) the mature ACP, composed of 78 amino acids, is a highly expressed protein (about 2.0-3.0 x 10(4) molecules per cell), (b) compared to E. coli ACP, it has a more compact structure and contains significantly more hydrophobic amino acid residues and (c) the potential mRNA sequence of the ACP gene has some structural features typical of a stable mRNA.

Polar allele duplication for transcriptional analysis of consecutive essential genes: application to a cluster of Escherichia coli fatty acid biosynthetic genes

The genes encoding acyl carrier protein and several key fatty acid biosynthetic enzymes are clustered at min 24 of the Escherichia coli chromosome. This cluster of genes is not transcribed as a classical operon, but rather multiple promoters are present and each gene is cotranscribed with at least one other gene. Transcripts specific for single genes ar also present. Transcription of acpP, the gene encoding acyl carrier protein, has been studied in detail. The acpP gene was shown to be transcribed from at least two different promoters by Northern (RNA) blot, primer extension, and deletion analyses, and the major promoter was mapped. We tested whether multiple promoters are necessary to produce acyl carrier protein by use of a new method whereby a transcriptional terminator was integrated into the chromosome upstream of the intact acpP gene. By use of this method (called polar allele duplication), we demonstrate that the promoter located immediately upstream of the coding sequence is sufficient for synthesis of this very abundant protein.

The apparent coupling between synthesis and posttranslational modification of Escherichia coli acyl carrier protein is due to inhibition of amino acid biosynthesis

Acyl carrier protein (ACP) is modified on serine 36 by the covalent posttranslational attachment of 4'-phosphopantetheine from coenzyme A (CoA), and this modification is required for lipid biosynthesis. Jackowski and Rock (J. Biol. Chem 258:15186-15191, 1983) reported that upon depletion of the CoA pool by starvation for a CoA precursor, no accumulation of the unmodified form of ACP (apo-ACP) was detected. We report that this lack of apo-ACP accumulation results from decreased translation of the acpP mRNAs because of the limitation of the synthesis of glutamate and other amino acids made directly from tricarboxylic acid cycle intermediates.

Isolation of Vibrio harveyi acyl carrier protein and the fabG, acpP, and fabF genes involved in fatty acid biosynthesis

We report the isolation of Vibrio harveyi acyl carrier protein (ACP) and cloning of a 3,973-bp region containing the fabG (encoding 3-ketoacyl-ACP reductase, 25.5 kDa), acpP (encoding ACP, 8.7 kDa), fabF (encoding 3-ketoacyl-ACP synthase II, 43.1 kDa), and pabC (encoding aminodeoxychorismate lyase, 29.9 kDa) genes. Predicted amino acid sequences were, respectively, 78, 86, 76, and 35% identical to those of the corresponding Escherichia coli proteins. Five of the 11 sequence differences between V. harveyi and E. coli ACP were nonconservative amino acid differences concentrated in a loop region between helices I and II.

Different respiratory-defective phenotypes of Neurospora crassa and Saccharomyces cerevisiae after inactivation of the gene encoding the mitochondrial acyl carrier protein

The nuclear genes (acp-1, ACP1) encoding the mitochondrial acyl carrier protein were disrupted in Neurospora crassa and Saccharomyces cerevisiae. In n. crassa acp-1 is a peripheral subunit of the respiratory NADH : ubiquinone oxidoreductase (complex I). S. cerevisiae lacks complex I and its ACP1 appears to be located in the mitochondrial matrix. The loss of acp-1 in N. crassa causes two biochemical lesions. Firstly, the peripheral part of complex I is not assembled, and the membrane part is not properly assembled. The respiratory ubiquinol : cytochrome c oxidoreductase (complex III) and cytochrome c oxidase (complex IV) are made in normal amounts. Secondly, the lysophospholipid content of mitochondrial membranes is increased four-fold. In S. cerevisiae, the loss of ACP1 leads to a pleiotropic respiratory deficient phenotype.

Molecular cloning and sequence analysis of a seed-expressed acyl carrier protein (ACP) gene from Brassica campestris (Agrani)

We describe here the nucleotide sequence of the Brassica campestris ACPSF1 gene which encodes a seed-expressed acyl carrier protein (ACP). The 3600 bp sequence consists of 1740 bp upstream of the translation start codon, 828 bp spanning the coding region which is interrupted by three introns and 1032 bp downstream of the stop codon. Using a ACPSF1 gene-specific probe, transcripts could be detected in developing seeds, but not in leaves. The gene is now the only known member that represents group I seed-expressed ACP multigene family of Brassica species. The 5' flanking sequence of the ACPSF1 gene was examined for putative transcriptional regulatory elements. A sequence alignment of the 5' flanking regions of the available seed-expressed ACP genes of Brassica species showed some conserved regions which might have some common regulatory significance.

Polyketide synthase acyl carrier proteins from Streptomyces: expression in Escherichia coli, purification and partial characterisation

Acyl carrier proteins (ACPs) of the type II polyketide synthases for the aromatic antibiotics actinorhodin, granaticin, frenolicin and oxytetracycline were expressed in Escherichia coli downstream of an inducible phage T7 promoter. For the act and otc genes, several of the first eight codons were changed to synonymous codons used in highly expressed E. coli genes. Correlated with these changes, the amounts of the act and otc ACPs purified from the recombinant E. coli cultures were an order of magnitude greater than for the gra and fren ACPs expressed from the unmodified genes. Electrospray mass spectrometry (ESMS) of the purified proteins confirmed their calculated M(r) based on the DNA sequences while also revealing that, in the act and gra ACP samples, some 2% and 30% of the holo-form of the protein was present (i.e., carrying the 4'-phosphopantetheine prosthetic group), with the remainder (and 100% of the otc and fren samples) being in the apo-form. Increasing incubation time post heat induction led to an increase in act holo-ACP. The recombinant act and gra ACPs could function in vitro as substrates for an S. coelicolor malonyl CoA:ACP acyl transferase, as measured by the coupling of a labelled malonyl unit to the ACP; their quantitative abilities to do so correlated with the proportions of deduced holo form in the two samples.

Overexpression, purification, and characterization of Escherichia coli acyl carrier protein and two mutant proteins

A synthetic gene of 237 bases encoding the 77-residue acyl carrier protein (ACP) from Escherichia coli, along with two mutant genes, ACP-I54V and ACP-A59V, were subcloned into the pET11a-pLysS E. coli overexpression system under the control of the bacteriophage T7 promoter. This efficient expression system and a simplified purification protocol yielded more than 120 mg/l of pure protein. The construct produced a mixture of holo-ACP and apo-ACP and two HPLC procedures were developed to separate the two species. This overexpression system allows cost-effective growths of 13C- and 15N-labeled protein for structural and other studies on ACP. In the course of the work on the mutants of ACP, an apparent homologous recombination event led, in one case, to reversion to a wild-type protein, suggesting that precautions to prevent such reversion should be taken.

Identification of domains in an Arabidopsis acyl carrier protein gene promoter required for maximal organ-specific expression

Deletions were made in the promoter of the acyl carrier protein (ACP) Acll.2 gene from Arabidopsis to investigate the nature of the cis-acting elements that direct its expression. These constructs, which included the untranslated leader region, were fused to a reporter gene coding for beta-glucuronidase (GUS) and transformed into tobacco. Quantitative fluorometric analysis of GUS activity in transgenic plants showed that expression in young leaves drops to a basal level when a 85 bp domain, from -320 to -236 relative to transcription initiation, is deleted. Maximum promoter activity in roots also depends on this domain, but two other regions are also important. In total, deletion of the sequences from -466 to -55 caused an ca. 80-fold reduction in Acl1.2 promoter activity in roots. The -320 to -236 domain forms a complex with a protein factor found in leaves and roots, which was not detectable in seeds. The formation of this protein-DNA complex was abolished by mutation of a bZIP core motif, ACGT, found within the context AAGACGTAG, which is dissimilar to the other bZIP-binding sites thus far characterized in plants. Previously we showed that Acl1.2 promoter activity is highest in seeds [2]. Here we find, in contrast to leaves and roots, that deletion to position -236 has no effect on GUS levels in seeds. However, nearly a 100-fold drop was observed when the -235 to -55 region was removed. Hence, this 180 bp domain contains all the cis-acting information necessary for Acl1.2 promoter activity in seeds. The same region is necessary for Acl1.2 activity in the receptacle, stigma, tapetum and pollen of the flower, as demonstrated by histochemical staining.

A method for examining expression of homologous genes in plant polyploids

One of the essential issues regarding evolution of polyploid species is how duplicate genes are expressed. Most studies on gene expression in polyploids have been based on isozyme analyses; RNA analysis has not been widely used partially due to difficulties in distinguishing homologous transcripts which usually have the same length and similar or almost identical sequences. In this study, a method combining RT-PCR with RFLP was used to analyze transcripts of homologous genes in natural and synthetic Brassica amphidiploids. Sequences coding for several known genes were selected and used to synthesize gene-specific primers. Total RNAs were used as templates for RT-PCR to amplify homologous transcripts in three diploid parental species, three cultivated amphidiploid species and six synthetic amphidiploids. For each gene, initial PCR products amplified in all species had identical length; however, homologous transcripts in the diploid and amphidiploid species could be distinguished after digesting the PCR products with restriction enzymes. Preliminary results based on three genes indicated that both transcripts from the diploid parents were expressed in the synthetic and natural amphidiploids. This study represents the first application of RT-PCR and RFLP analysis to investigate expression of homologous genes in higher plants. The technique is a sensitive, simple and efficient method for distinguishing homologous transcripts in a mixed RNA population and can be applied to many types of studies on expression of homologous genes.

The characterization of a mitochondrial acyl carrier protein isoform isolated from Arabidopsis thaliana

A cDNA clone was isolated from an Arabidopsis leaf cDNA library that shared a high degree of protein sequence identity with mitochondrial acyl carrier proteins (mtACPs) isolated from Neurospora crassa and bovine heart muscle. The cDNA encoded an 88-amino acid mature protein that was preceded by a putative 35-amino acid presequence. In vitro protein import studies have confirmed that the presequence specifically targets this protein into pea mitochondria but not into chloroplasts. These studies indicated that pea mitochondria were not only able to import and process the precursor protein but also possessed the ability to acylate the mature protein. The mitochondrial localization of this protein, mtACP-1, was confirmed by western blot analysis. Arabidopsis mitochondrial protein extracts contained two cross-reacting bands that comigrated with the mature mtACP-1 and acylated mtACP-1 proteins. The acylated form of mtACP-1 was approximately 4 times more abundant than the unacylated form and appeared to be localized predominantly in the mitochondrial membrane where the unacylated mtACP-1 was present mostly in the matrix fraction. A chloroplast fatty acid synthase system was used, and mtACP-1 was able to function as a cofactor for fatty acid synthesis. However, predominantly short- and medium-chain fatty acids were produced in fatty acid synthase reactions supplemented with mtACP-1, suggesting that mtACP-1 may be causing premature fatty acid chain termination.

Block searches on VAX and Alpha computer systems

A new program, BlockSearch, is described that allows biologists to search protein sequences against the BLOCKS database of aligned protein blocks by converting these blocks to site-specific scoring matrices. It thus complements existing tools for standard similarity searches and pattern searches which aid in elucidating the function of newly determined protein-coding sequences. The speed of the program and the existence of a command-line interface render BlockSearch particularly interesting for the batch analysis of many new sequences, such as collections of expressed sequence tags. Although written primarily for Digital's Alpha and VAX systems, the code is easily portable to other platforms.

Purification and separation of holo- and apo-forms of Saccharopolyspora erythraea acyl-carrier protein released from recombinant Escherichia coli by freezing and thawing

Saccharopolyspora erythraea acyl-carrier protein, highly expressed from a T7-based expression plasmid in Escherichia coli, can be selectively released from the cells in near-quantitative yield by a single cycle of freezing and thawing in a neutral buffer. Electrospray mass spectrometry was used to confirm that the recombinant S. erythraea acyl-carrier protein over-expressed in E. coli is present predominantly as the holo-form, with variable amounts of apo-acyl-carrier protein, holo-acyl-carrier protein dimer and holo-acyl-carrier protein glutathione adduct. The holo- and apo-acyl-carrier proteins are both readily purified on a large scale from the freeze-thaw extracts and can be separated from one another by octyl-Sepharose chromatography. The holo-acyl-carrier protein obtained in this way was fully active in supporting the synthesis of acyl-acyl-carrier protein by extracts of S. erythraea.

DNA sequence analysis of the YCN2 region of chromosome XI in Saccharomyces cerevisiae

A 6.8 kbp DNA fragment localized to the left arm of chromosome XI from Saccharomyces cerevisiae was sequenced and analysed (EMBL accession no. X69765). Two genes involved in protein phosphatase activity were identified: YCN2 and an open reading frame encoding a protein that shares 46% amino acid identity with the sds22+ protein from Schizosaccharomyces pombe. A comparison of the genomic YCN2 sequence with the published cDNA sequence suggests the presence of an intron near the 5' end of the gene. Further sequence analysis suggests the presence of three additional genes near YCN2: a mitochondrial acyl-carrier protein, a gene encoding a putative hydrophobic protein, and a new gene coding for a tRNA(Leu) (UAA) isoacceptor located near a delta sequence.

Developmental regulation of an acyl carrier protein gene promoter in vegetative and reproductive tissues

The expression of an Arabidopsis acyl carrier protein (ACP) gene promoter has been examined in transgenic tobacco plants by linking it to the reporter gene beta-glucuronidase (GUS). Fluorometric analysis showed that the ACP gene promoter was most active in developing seeds. Expression was also high in roots, but significantly lower in young leaves and downregulated upon their maturation. Etiolated and light-grown seedlings showed the same level of GUS activity, indicating that this promoter is not tightly regulated by light. Histochemical studies revealed that expression was usually highest in apical/meristematic zones of vegetative tissues. Young flowers (ca. 1 cm in length) showed GUS staining in nearly all cell types, however, cell-specific patterns emerged in more mature flowers. The ACP gene promoter was active in the stigma and transmitting tissue of the style, as well as in the tapetum of the anther, developing pollen, and ovules. The results provide evidence that this ACP gene is regulated in a complex manner and is responsive to the array of signals which accompany cell differentiation, and a demand for fatty acids and lipids, during organogenesis.

Genetic construction and functional analysis of hybrid polyketide synthases containing heterologous acyl carrier proteins

The gene that encodes the acyl carrier protein (ACP) of the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor A3(2) was replaced with homologs from the granaticin, oxytetracycline, tetracenomycin, and putative frenolicin polyketide synthase gene clusters. All of the replacements led to expression of functional synthases, and the recombinants synthesized aromatic polyketides similar in chromatographic properties to actinorhodin or to shunt products produced by mutants defective in the actinorhodin pathway. Some regions within the ACP were also shown to be interchangeable and allow production of a functional hybrid ACP. Structural analysis of the most abundant polyketide product of one of the recombinants by electrospray mass spectrometry suggested that it is identical to mutactin, a previously characterized shunt product of an actVII mutant (deficient in cyclase and dehydrase activities). Quantitative differences in the product profiles of strains that express the various hybrid synthases were observed. These can be explained, at least in part, by differences in ribosome-binding sites upstream of each ACP gene, implying either that the ACP concentration in some strains is rate limiting to overall PKS activity or that the level of ACP expression also influences the expression of another enzyme(s) encoded by a downstream gene(s) in the same operon as the actinorhodin ACP gene. These results reaffirm the idea that construction of hybrid polyketide synthases will be a useful approach for dissecting the molecular basis of the specificity of PKS-catalyzed reactions. However, they also point to the need for reducing the chemical complexity of the approach by minimizing the diversity of polyketide products synthesized in strains that produce recombinant polyketide synthases.

Targeted gene replacements in a Streptomyces polyketide synthase gene cluster: role for the acyl carrier protein

A methodology was developed to construct any desired chromosomal mutation in the gene cluster that encodes the actinorhodin polyketide synthase (PKS) of Streptomyces coelicolor A3(2). A positive selection marker (resistance gene) is first introduced by double crossing-over into the chromosomal site of interest by use of an unstable delivery plasmid. This marker is subsequently replaced by the desired mutant allele via a second high-frequency double recombination event. The technology has been used to: (i) explore the significance of translational coupling between two adjacent PKS genes; (ii) prove that the acyl carrier protein (ACP) encoded by a gene in the cluster is necessary for the function of the actinorhodin PKS; (iii) provide genetic evidence supporting the hypothesis that serine 42 is the site of phosphopantetheinylation in the ACP of the actinorhodin PKS; and (iv) demonstrate that this ACP can be replaced by a Saccharopolyspora fatty acid synthase ACP to generate an active hybrid PKS.

Nucleotide sequence and deduced functions of a set of cotranscribed genes of Streptomyces coelicolor A3(2) including the polyketide synthase for the antibiotic actinorhodin

A 5.3-kb region of the Streptomyces coelicolor actinorhodin gene cluster, including the genes for polyketide biosynthesis, was sequenced. Six identified open reading frames (ORF1-6) were related to genetically characterized mutations of classes actI, VII, IV, and VB by complementation analysis. ORF1-6 run divergently from the adjacent actIII gene, which encodes the polyketide synthase (PKS) ketoreductase, and appear to form an operon. The deduced gene products of ORF1-3 are similar to fatty acid synthases (FAS) of different organisms and PKS genes from other polyketide producers. The predicted ORF5 gene product is similar to type II beta-lactamases of Bacillus cereus and Bacteroides fragilis. The ORF6 product does not resemble other known proteins. Combining the genetical, biochemical, and similarity data, the potential activities of the products of the six genes can be postulated as: 1) condensing enzyme/acyl transferase (ORF1 + ORF2); 2) acyl carrier protein (ORF3); 3) putative cyclase/dehydrase (ORF4); 4) dehydrase (ORF5); and 5) "dimerase" (ORF6). The data show that the actinorhodin PKS consists of discrete monofunctional components, like that of the Escherichia coli (Type II) FAS, rather than the multifunctional polypeptides for the macrolide PKSs and vertebrate FASs (Type I).

The isolation and functional characterisation of a B. napus acyl carrier protein 5' flanking region involved in the regulation of seed storage lipid synthesis

Acyl carrier protein (ACP) is a key component of the fatty acid biosynthetic machinery in plants. A 1.4 kb 5' flanking region of a Brassica napus ACP gene (ACP05) was transcriptionally fused to the reporter gene beta-glucuronidase (GUS), and expression of the chimeric gene monitored in transgenic tobacco. GUS activity was found to increase through seed development reaching a maximum value, coincident with the most active phase of storage lipid synthesis that was, on average, 100-fold higher than that observed in leaf. In control plants transformed with CaMV 35S-GUS constructs, GUS activity was similar in leaf and all stages of seed development. Based on average values, the level of GUS expression obtained via the ACP promoter was comparable to that obtained from the CaMV 35S promoter. We therefore conclude that the isolated 5' ACP flanking sequence represents a strong promoter element involved in the developmental regulation of storage lipid synthesis in B. napus seed tissue. Putative regulatory elements in the 5' upstream region of ACP05 were identified by dot matrix analysis and by sequence comparison with the upstream regions from a second seed-expressed rape ACP gene and from an Arabidopsis ACP gene.

The gene encoding Escherichia coli acyl carrier protein lies within a cluster of fatty acid biosynthetic genes

The gene encoding Escherichia coli acyl carrier protein (ACP) has been isolated and sequenced. The ACP gene (called acpP) was located on the genetic map between fabF and fabD which encode two fatty acid biosynthetic enzymes, 3-ketoacyl-ACP synthase II and malonyl CoA-ACP transacylase, respectively. An open reading frame between acpP and fabD encodes a 26.5-kDa protein that has significant sequence identity (greater than 40%) with two acetoacetyl-CoA reductases and thus is believed to encode a 3-ketoacyl-ACP reductase. This gene (called fabG) is cotranscribed with acpP. Thus, the gene encoding ACP, the key carrier protein of fatty acid synthesis, is located within a cluster of fatty acid biosynthetic genes.

The plastid genome of Cryptomonas phi encodes an hsp70-like protein, a histone-like protein, and an acyl carrier protein

The plastid genome of Cryptomonas phi, a cryptomonad alga, contains three genes that have not previously been found in any organellar genome. Each of these genes encodes a functional class of organellar gene product not previously reported. The first gene, dnaK, encodes a polypeptide of the hsp70 heat shock protein family. The predicted amino acid sequence of the DnaK protein is 54% identical to that of the Escherichia coli hsp70 protein (DnaK), 50-53% identical to that of two nucleus-encoded mitochondrial hsp70 proteins, and 43-46% identical to that of several eukaryotic cytoplasmic members of the hsp70 protein family. The second gene, hlpA, encodes a polypeptide resembling bacterial histone-like proteins. The predicted amino acid sequence of the HlpA protein is 25-53% identical to that of several bacterial histone-like proteins, and the identity increases to 39-76% over a conserved region corresponding to the long arm that binds DNA. The third gene, acpA, encodes an acyl carrier protein, which is a key cofactor in the synthesis and metabolism of fatty acids. Its predicted amino acid sequence is 36-59% identical to that of eubacterial and plant chloroplast (nucleus-encoded) acyl carrier proteins.

Overproduction and localization of components of the polyketide synthase of Streptomyces glaucescens involved in the production of the antibiotic tetracenomycin C

Three proteins, including the beta-keto acyl synthase and the acyl carrier protein, involved in the synthesis of the polyketide antibiotic tetracenomycin C by Streptomyces glaucescens GLA.0 were produced in Escherichia coli by using the T7 RNA polymerase-dependent pT7-7 expression vector. Changing the N-terminal codon usage of two of the genes greatly increased the level of protein produced without affecting mRNA levels, suggesting improvements in translational efficiency. Western immunoblot analysis of cytoplasmic and membrane fractions of S. glaucescens with antibodies raised to synthetic oligopeptides corresponding to the two presumed components of the beta-keto acyl synthase indicated that both proteins were membrane bound; one appears to be proteolytically cleaved before or during association with the membrane. The beta-keto acyl synthase could be detected in stationary-phase cultures but not in rapidly growing cultures, correlating with the time of appearance of tetracenomycin C in the medium.

The acyl-carrier protein in Neurospora crassa mitochondria is a subunit of NADH:ubiquinone reductase (complex I)

We determined the primary structure of a 9.6-kDa subunit of the respiratory chain NADH:ubiquinone reductase (complex I) from Neurospora crassa mitochondria and found a close relationship between this subunit and the bacterial or chloroplast acyl-carrier protein. The degree of sequence identity amounts to 80% in a region of 19 residues around the serine to which the phosphopantetheine is bound. The N-terminal presequence of the subunit has the characteristic features of a mitochondrial import sequence. We cultivated the auxotroph pan-2 mutant of N. crassa in the presence of [14C]pantothenate and recovered all radioactivity incorporated into mitochondrial protein in the 9.6-kDa subunit of complex I. We cultivated N. crassa in the presence of chloramphenicol to accumulate the nuclear-encoded peripheral arm of complex I. This pre-assembled arm also contains the 9.6-kDa subunit. These results demonstrate that an acyl-carrier protein with pantothenate as prosthetic group is a constituent part of complex I in N. crassa.

Presence of an acyl carrier protein in NADH:ubiquinone oxidoreductase from bovine heart mitochondria

The amino-acid sequence of a subunit of NADH:ubiquinone oxidoreductase from bovine heart mitochondria has been determined and is closely related to those of acyl carrier proteins that are involved in fatty acid biosynthesis in Escherichia coli and plants. Evidence for the presence of covalently attached pantetheine-4'-phosphate in the bovine protein has been obtained by determination of the molecular mass of the isolated subunit by electrospray mass spectrometry, before and after incubation of the protein at alkaline pH under reducing conditions. This decreased the molecular mass from 10,751.6 to 10,449.4, a difference of 302.2 mass units; the value calculated from the protein sequence with one covalently attached pantetheine-4'-phosphate is 10,449.8. The acyl group which is removed by alkaline reduction, appears to be attached via a thioester linkage. By analogy with the bacterial protein it is likely that the attachment site of the pantetheine-4-phosphate is serine-44, which is found in a highly conserved region of the sequence. At present the function of the acyl carrier protein in mitochondrial complex I is not understood.

Acyl carrier protein-derived sequence encoded by the chloroplast genome in the marine diatom Cylindrotheca sp. strain N1

The chloroplast genome of chromophytic and rhodophytic algae differs from the plastid genome of plants and green algae in that it encodes the gene for the small subunit (rbcS) of ribulose 1,5-bisphosphate carboxylase/oxygenase. Hybridization studies indicated that there was a second region of chloroplast DNA from the marine diatom Cylindrotheca sp. strain N1 that strongly hybridized to a previously isolated Cylindrotheca fragment that contained the rbcS gene and flanking sequences. Subsequent determination of the oligonucleotide sequence of this second chloroplast DNA fragment, however, indicated that hybridization was due to identical sequences 3' to the previously cloned Cylindrotheca chloroplast rbcL rbcS genes. Sequences derived from the 5' end of the second chloroplast DNA fragment contained a short open reading frame of 80 amino acids which was found to be highly homologous to bacterial acyl carrier protein and nuclear-encoded acyl carrier protein from plants. Amino acid residues in the environment of Ser-36 of the Escherichia coli protein, which is bound to a 4'-phosphopantetheine moiety, are virtually identical in the Cylindrotheca deduced sequence and all other sources of this protein. Unlike plant acyl carrier-deduced amino acid sequences, there was no leader peptide sequence found for the presumptive Cylindrotheca protein, consistent with the location of this DNA fragment on the chloroplast genome of this organism. DNA encoding the putative acyl carrier protein gene and rbcS thus represent two genes that are chloroplast-encoded in the chromophytic marine diatom Cylindrotheca, a significant departure from the organization of such genes in plants.

Cloning, characterization, and high-level expression in Escherichia coli of the Saccharopolyspora erythraea gene encoding an acyl carrier protein potentially involved in fatty acid biosynthesis

The erythromycin A-producing polyketide synthase from the gram-positive bacterium Saccharopolyspora erythraea (formerly Streptomyces erythraeus) has evident structural similarity to fatty acid synthases, particularly to the multifunctional fatty acid synthases found in eukaryotic cells. Fatty acid synthesis in S. erythraea has previously been proposed to involve a discrete acyl carrier protein (ACP), as in most prokaryotic fatty acid synthases. We have cloned and sequenced the structural gene for this ACP and find that it does encode a discrete small protein. The gene lies immediately adjacent to an open reading frame whose gene product shows sequence homology to known beta-ketoacyl-ACP synthases. A convenient expression system for the S. erythraea ACP was obtained by placing the gene in the expression vector pT7-7 in Escherichia coli. In this system the ACP was efficiently expressed at levels 10 to 20% of total cell protein. The recombinant ACP was active in promoting the synthesis of branched-chain acyl-ACP species by extracts of S. erythraea. Electrospray mass spectrometry is shown to be an excellent method for monitoring the efficiency of in vivo posttranslational modification of ACPs.

Acyl carrier protein import into chloroplasts. Both the precursor and mature forms are substrates for phosphopantetheine attachment by a soluble chloroplast holo-acyl carrier protein synthase

Recently a chloroplast holo-acyl carrier protein (holoACP) synthase activity was identified which attached the phosphopantetheine prosthetic group to acyl carrier protein, producing holoACP (Fernandez and Lamppa (1990) Plant Cell 2, 195-206). Here we show that the mature form of ACP (apoACP), after entry into the chloroplast and removal of the transit peptide, is a substrate for modification by the holoACP synthase. Modification occurs optimally at 37 degrees C and is inhibited by 5 mM 3',5'-ADP and 2 mM EDTA. An ACP construct (matACP) lacking the transit peptide was also converted to the holoACP form in an organelle-free assay, independent of precursor cleavage. The matACP construct was used to monitor the chromatographic separation of the holoACP synthase from the transit peptidase. Superose 12 gel filtration analysis indicates that the holoACP synthase has an apparent Mr of approximately 50,000. Using fractions enriched for the holoACP synthase it was demonstrated that the precursor of ACP is also modified in the presence of CoA and subsequently can be proteolytically processed directly to holoACP. Kinetic analysis, however, indicates that removal of the transit peptide is a much faster reaction than phosphopantetheine addition, suggesting that apoACP is the primary substrate for the chloroplast holoACP synthase in vivo.

Purification and characterization of acyl carrier protein from two cyanobacteria species

The acyl carrier protein (ACP), an essential protein cofactor for fatty acid synthesis, has been isolated from two cyanobacteria: the filamentous, heterocystous, Anabaena variabilis (ATCC 29211) and the unicellular Synechocystis 6803 (ATCC 27184). Both ACPs have been purified to homogeneity utilizing a three-column procedure. Synechocystis 6803 ACP was purified 1800-fold with 67% yield, while A. variabilis ACP was purified 1040-fold with 50% yield. Yields of 13.0 micrograms ACP/g Synechocystis 6803 and 9.0 micrograms ACP/g A. variabilis were achieved. Amino acid analysis indicated that these ACPs were highly charged acidic proteins similar to other known ACPs. Sequence analysis revealed that both cyanobacterial ACPs were highly conserved with both spinach and Escherichia coli ACP at the phosphopantetheine prosthetic group region. Examining the probability of alpha-helix and beta-turn regions in various ACPs, showed that cyanobacterial ACPs were more closely related to E. coli ACP than spinach ACP I. Immunoblot analysis and a competitive binding assay for ACP illustrated that both ACPs bound poorly to spinach ACP I antibody. SDS/PAGE and native PAGE of Synechocystis 6803 ACP and A. variabilis ACP showed that cyanobacteria ACPs co-migrated with E. coli ACP and had relative molecular masses of 18,100 and 17,900 respectively. Both native and urea gel analysis of acyl-ACP products from fatty acid synthase reactions demonstrated that bacterial ACPs and plant ACP gave essentially the same metabolic products when assayed using either bacterial or plant fatty acid synthase. A. variabilis and Synechocystis 6803 ACP could be acylated using E. coli acyl ACP synthetase.

Acyl carrier protein (ACP) import into chloroplasts does not require the phosphopantetheine: evidence for a chloroplast holo-ACP synthase

Import of the acyl carrier protein (ACP) precursor into the chloroplast resulted in two products of about 14 kilodalton (kD) and 18 kD when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Time course experiments indicate that the latter is a modification derivative of the 14-kD peptide after the removal of the transit peptide. Substitution of serine 38 by alanine, eliminating the phosphopantetheine prosthetic group attachment site of ACP, produced a precursor mutant that gave rise to only the 14-kD peptide during import, showing that the modified form depends on the presence of serine 38. Furthermore, these results demonstrate that the prosthetic group is not essential for ACP translocation across the envelope or proteolytic processing. Analysis of the products of import by nondenaturing, conformationally sensitive gels showed reversal of the relative mobility of the 14-kD peptide and the modified form, raising the possibility that the modification is the addition of the phosphopantetheine. Proteolytic processing and the modification reaction were reconstituted in an organelle-free assay. The addition of coenzyme A to the organelle-free assay completely converted the 14-kD peptide to the modified form at 10 micromolar, and this only occurred with the wild-type substrate. Reciprocally, treatment of the products of a modification reaction with Escherichia coli phosphodiesterase converted the modified ACP from back to the 14-kD peptide. These results strongly support the conclusion that there is a holo-ACP synthase in the soluble compartment of the chloroplast capable of transferring the phosphopantetheine of coenzyme A to ACP.

Characterization of recombinant thioesterase and acyl carrier protein domains of chicken fatty acid synthase expressed in Escherichia coli

Fatty acid synthase of animal tissue is a multifunctional enzyme comprised of two identical subunits, each containing seven partial activities and a site for the prosthetic group, 4'-phosphopantetheine (acyl carrier protein). We have recently isolated cDNA clones of chicken fatty acid synthase coding for the dehydratase, enoyl reductase, beta-ketoacyl reductase, acyl carrier protein, and thioesterase domains (Chirala, S.S., Kasturi, R., Pazirandeh, M., Stolow, D.T., Huang, W.Y., and Wakil, S.J. (1989) J. Biol. Chem. 264, 3750-3757). To gain insight into the structure and function of the various domains, the portion of the cDNA coding for the acyl carrier protein and thioesterase domains was expressed in Escherichia coli by using an expression vector that utilizes the phage lambda PL promoter. The recombinant protein was efficiently expressed and purified to near homogeneity using anion-exchange and hydroxyapatite chromatography. As expected from the coding capacity of the cDNA expressed, the protein has a molecular weight of 43,000 and reacts with antithioesterase antibodies. The recombinant thioesterase was found to be enzymatically active and has the same substrate specificity and kinetic properties as the native enzyme of the multifunctional synthase. Treatment of the recombinant protein with alpha-chymotrypsin results in the cleavage of the acyl carrier protein and thioesterase domain junction sequence at exactly the same site as with native fatty acid synthase. The amino acid composition of the purified recombinant protein revealed the presence of 0.6 mol of beta-alanine/mol of protein, indicating partial pantothenylation of the recombinant acyl carrier protein domain. These results indicate that the expressed protein has a conformation similar to the native enzyme and that its folding into functionally active domains is independent of the remaining domains of the multifunctional synthase subunit. These conclusions are consistent with the proposal that the multifunctional synthase gene has evolved from fusion of component genes.

Site-directed mutagenesis of the spinach acyl carrier protein-I prosthetic group attachment site

Site-directed mutagenesis was used to change the phosphopantetheine attachment site (Ser38) of spinach acyl carrier protein I (ACP-I) from a serine to a threonine or cysteine residue. 1. Although the native ACP-I is fully phosphopantethenylated when expressed in Escherichia coli, the TH-ACP-I and CY-ACP-I mutants were found to be completely devoid of the phosphopantetheine group. Therefore, the E. coli holoACP synthase requires serine for in vivo phosphopantetheine addition to spinach ACP-I. 2. Spinach holoACP synthase was completely inactive in vitro with either the TH-ACP-I or CY-ACP-I mutants. In addition, TH-ACP-I and CY-ACP-I were strong inhibitors of spinach holoACP synthase. 3. The mutant ACPs were weak or ineffective as inhibitors of spinach fatty acid synthesis and spinach oleoyl-ACP hydrolase. 4. Compared to holoACP-I, the mutant apoACP-I analogs had: (a) altered mobility in SDS and native gel electrophoresis, (b) altered binding to anti-(spinach ACP-I) antibodies and (c) altered isoelectric points. The combined physical, immunological and enzyme inhibition data indicate that attachment of the phosphopantheine prosthetic group alters ACP conformation.

Expression of holo and apo forms of spinach acyl carrier protein-I in leaves of transgenic tobacco plants

Acyl carrier protein (ACP) is a chloroplast-localized cofactor of fatty acid synthesis, desaturation, and acyl transfer. We have transformed tobacco with a chimeric gene consisting of the tobacco ribulose-1,5-bisphosphate carboxylase promoter and transit peptide and the sequence encoding the mature spinach ACP-I. Spinach ACP-I was expressed in the transformed plants at levels twofold to threefold higher than the endogenous tobacco ACPs as determined by protein immunoblots and assays of ACP in leaf extracts. In addition to these elevated levels of the holo form, there were high levels of apoACP-I, a form lacking the 4'-phosphopantetheine prosthetic group and not previously detected in vivo. The mature forms of both apoACP-I and holoACP-I were located in the chloroplasts, indicating that the transit peptide was cleaved and that attachment of the prosthetic group was not required for uptake into the plastid. There were also significant levels of spinach acyl-ACP-I, demonstrating that spinach ACP-I participated in tobacco fatty acid metabolism. Lipid analyses of the transformed plants indicated that the increased ACP levels caused no significant alterations in leaf lipid biosynthesis.

Plastid-localised seed acyl-carrier protein of Brassica napus is encoded by a distinct, nuclear multigene family

Acyl-carrier protein (ACP) is a key component involved in the regulation of fatty acid biosynthesis in plants. cDNA clones encoding ACP from Brassica napus (oil seed rape) embryos have been isolated using oligonucleotide probes derived from heterologous ACPs. Analysis of the DNA sequence data, in conjunction with N-terminal amino acid sequence data, revealed ACP to be synthesized from nuclear DNA as a precursor containing a 51-amino-acid N-terminal extension. Immunocytochemical studies showed ACP to be localised solely within the plastids of B. napus seed tissue and it would therefore appear that the N-terminal extension functions as a transit peptide to direct ACP into these organelles. Analysis of several cDNA clones revealed sequence heterogeneity and thus evidence for an ACP multigene family. From ten cDNA clones, six unique genes, encoding five different mature ACP polypeptides, were identified. Northern blot hybridisation studies provide evidence that the seed and leaf forms of rape ACP are encoded by structurally distinct gene sets.

Purification and characterization of recombinant spinach acyl carrier protein I expressed in Escherichia coli

Expression of plant acyl carrier protein (ACP) in Escherichia coli at levels above that of constitutive E. coli ACP does not appear to substantially alter bacterial growth or fatty acid metabolism. The plant ACP expressed in E. coli contains pantetheine and approximately 50% is present in vivo as acyl-ACP. We have purified and characterized the recombinant spinach ACP-I. NH2-terminal amino acid sequencing indicated identity to authentic spinach ACP-I, and there was no evidence for terminal methionine or formylmethionine. Recombinant ACP-I was found to completely cross-react immunologically with polyclonal antibody raised to spinach ACP-I. Recombinant ACP-I was a poor substrate for E. coli fatty acid synthesis. In contrast, Brassica napus fatty acid synthetase gave similar reaction rates with both recombinant and E. coli ACP. Similarly, malonyl-coenzyme A:acyl carrier protein transacylase isolated from E. coli was only poorly able to utilize the recombinant ACP-I while the same enzyme from B. napus reacted equally well with either E. coli ACP or recombinant ACP-I. E. coli acyl-ACP synthetase showed a higher reaction rate for recombinant ACP-I than for E. coli ACP. Expression of spinach ACP-I in E. coli provides, for the first time, plant ACP in large quantities and should aid in both structural analysis of this protein and in investigations of the many ACP-dependent reactions of plant lipid metabolism.

A small, discrete acyl carrier protein is involved in de novo fatty acid biosynthesis in Streptomyces erythraeus

A heat-stable factor, required for de novo synthesis of fatty acids in the erythromycin-producing organism Streptomyces erythraeus, has been purified to homogeneity and identified as an acyl carrier protein (ACP). We conclude that, contrary to previous belief, fatty acid synthase in S. erythraeus more closely resembles the dissociable complex of E. coli than the tightly associated, multifunctional enzyme complex found in the related actinomycete Mycobacterium smegmatis.

Synthesis, cloning, and expression in Escherichia coli of a spinach acyl carrier protein-I gene

A synthetic gene of 268 bp encoding the 82 amino acid spinach acyl carrier protein (ACP)-I was constructed based on the known amino acid sequence. Two gene fragments, one encoding the amino-terminal portion and the other the carboxy-terminal portion of the protein, were assembled from synthetic oligonucleotides and inserted into the phage M13mp19. These partial gene constructions were joined and inserted into the plasmid pTZ19R. DNA sequencing confirmed the accuracy of the constructions. The synthetic gene was then subcloned into the Escherichia coli expression vector pKK233-2, under the control of the trc promoter. Western blot analysis and radioimmunoassay indicated that E. coli cells carrying this plasmid produced up to 6 mg/liter of a protein which was immunologically cross-reactive and similar in electrophoretic mobility to authentic spinach acyl carrier protein. The bacterial cells were able to attach the phosphopantetheine prosthetic group to the synthetic plant gene product allowing it to be acylated in vitro by acyl-ACP synthetase.

Molecular cloning and sequencing of a cDNA encoding the acyl carrier protein and its flanking domains in the mammalian fatty acid synthetase

Cloned cDNAs containing coding sequences for domains proximal to the carboxy terminus of the rat fatty acid synthetase have been isolated using an expression vector and domain-specific antibodies. The coding regions were assigned to specific domains of the multifunctional complex by identification of sequences coding for characterized peptide fragments and by recognition of sequences homologous to other monofunctional enzymes. Two clones contain the entire coding region for the acyl carrier protein domain. The sequence is flanked at the 3'-end by a region coding for the thioesterase domain and at the 5'-end by a sequence coding for a reductase, most likely the ketoreductase domain. Thus the ordering of these domain-coding regions in the fatty acid synthetase mRNA is established. The acyl carrier protein domain exhibits about 25% homology with that of the discrete monofunctional acyl carrier proteins of Escherichia coli, spinach and barley, the ketoreductase domain exhibits about 25% homology with bacterial dihydrofolate reductases and the active site of the thioesterase domain exhibits both primary and secondary structural features common to the serine proteases. These findings lend support to the hypothesis that the polyfunctional fatty acid synthetase probably arose by a complex evolutionary process involving fusion of genes coding for seven individual enzymes.

Oligonucleotide probes for bacterial acylcarrier protein genes

Using a recently-introduced rapid manual method, we have synthesized a family of thirty six individual oligonucleotides of unique sequence (18-mers), which correspond to the conserved amino acid sequence, GADSLD, found at the 4'-phosphopantetheine-binding site of the acylcarrier component of bacterial and plant fatty acid synthases. Hybridisation of each of these oligonucleotides to Southern blots of restricted Streptomyces erythreus DNA under stringent conditions showed that (i) only two probes hybridised specifically, (ii) neither probe hybridised to more than one sequence, and (iii) each probe apparently recognised a different DNA sequence. In the same synthesis, ninety-two other oligonucleotides (15-18-mers) were also constructed, mostly in yields of 2-10%.

Evidence that incorporation of exogenous fatty acids into the phospholipids of Escherichia coli does not require acyl carrier protein

Cells of an Escherichia coli acpS mutant were prepared with decreased intracellular concentrations (to 10% of the normal level) of the holo form of acyl carrier protein. These cells incorporated exogenous oleic acid into phospholipid at a normal rate.

A mutant of Escherichia coli conditionally defective in the synthesis of holo-[acyl carrier protein]

Supplementation of Escherichia coli pantothenate auxotrophs with varying concentrations of pantothenate results in a concomitant variation of the intracellular level of CoA but has no effect on the level of holo-[acyl carrier protein] (holo-[ACP]) (Alberts, A., and Vagelos, P. R. (1966) J. Biol. Chem. 241, 5201-5204). The 4-phosphopantetheine moiety of CoA is transferred by the enzyme holo-[ACP] synthase to apo-[acyl carrier protein] (apo-[ACP]) to form holo-[ACP], the form active in lipid synthesis. We mutagenized an E. coli K12 pantothenate auxotroph and selected for mutants unable to grow on a low concentration of pantothenate (0.25 microM) but that grew on a much higher level (25 microM). One of these strains was completely deficient in holo-[ACP] synthase. Reversion and recombinational genetic analyses indicated that the mutant growth phenotype was due to an altered holo-[ACP] synthase activity. The changes in the intracellular levels of CoA and holo-[ACP] engendered by manipulation of the levels of pantothenate supplementation were consistent with a deficiency in holo-[ACP] synthase activity in cultures supplemented with low levels of pantothenate. The site of the genetic lesion (called acpS) was localized on the E. coli genetic map.

Biochemical and genetic characterization of an auxotroph of Bacillus subtilis altered in the Acyl-CoA:acyl-carrier-protein transacylase

We have analyzed a mutation of Bacillus subtilis (bfmB) that results in an acyl-CoA:acyl-carrier-protein transacylase with low affinity for branched acyl-CoA substrates; it maps in the acf-hisH region of the chromosome. The aceA mutation, present in the parent of the bfmB mutant, causes a deficiency in pyruvate dehydrogenase and maps in the pycA-pyrA region. Strains carrying the bfmB mutation synthesize branched-chain fatty acids at a rate sufficient for normal growth only if branched acyl-CoA precursors are present in the medium. They grow well if the medium is supplemented with 0.1 mM 2-methylbutyrate, isobutyrate or isovalerate, or with 1.0 mM isoleucine or valine; leucine does not support growth. Growth supported by valine and isoleucine is inhibited by butyrate and other straight short-chain fatty acids at concentrations (0.1 mM) which do not inhibit growth of the standard strain; the inhibition is prevented by short branched fatty acids which are converted to long-chain fatty acids appearing as activity of B. subtilis is controlled by separate enzymatic sites for the acyl-CoA precursors of branched and straight-chain fatty acids. Whether these sites are contained in one or two enzymes is not known.