Genomic structures and characterization of the 5'-flanking regions of acyl carrier protein and Delta4-palmitoyl-ACP desaturase genes from Coriandrum sativum

The seed-specific or seed-predominant promoters of acyl carrier protein (Cs-ACP1) and Delta4-palmitoyl-acyl carrier protein desaturase (Cs-4PAD) genes, which are involved in the biosynthesis of petroselinic acid, were isolated from coriander (Coriandrum sativum) and analyzed in coriander endosperms and transgenic Arabidopsis. The expression of Cs-ACP1 and Cs-4PAD genes was coordinately regulated during seed development.

Organization of the biosynthetic gene cluster for the macrolide concanamycin A in Streptomyces neyagawaensis ATCC 27449

The macrolide antibiotic concanamycin A has been identified as an exceptionally potent inhibitor of the vacuolar (V-type) ATPase. Such compounds have been mooted as the basis of a potential drug treatment for osteoporosis, since the V-ATPase is involved in the osteoclast-mediated bone resorption that underlies this common condition. To enable combinatorial engineering of altered concanamycins, the biosynthetic gene cluster governing the biosynthesis of concanamycin A has been cloned fromStreptomyces neyagawaensisand shown to span a region of over 100 kbp of contiguous DNA. An efficient transformation system has been developed forS. neyagawaensisand used to demonstrate the role of the cloned locus in the formation of concanamycin A. Sequence analysis of the 28 ORFs in the region has revealed key features of the biosynthetic pathway, in particular the biosynthetic origin of portions of the backbone, which arise from the unusual polyketide building blocks ethylmalonyl-CoA and methoxymalonyl-ACP, and the origin of the pendant deoxysugar moiety 4′-O-carbamoyl-2′-deoxyrhamnose, as well as the presence of a modular polyketide synthase (PKS) encoded by six giant ORFs. Examination of the methoxymalonyl-specific acyltransferase (AT) domains has led to recognition of an amino acid sequence motif which can be used to distinguish methylmalonyl-CoA- from methoxymalonyl-ACP-specific AT domains in natural PKSs.

Peptide nucleic acid antisense oligomer as a therapeutic strategy against bacterial infection: proof of principle using mouse intraperitoneal infection

Antisense oligodeoxynucleotides (ODNs) and their analogs have been successfully utilized to inhibit gene expression and bacterial growth in vitro or in cell culture. In this study, acpP-targeting antisense peptide nucleic acid (PNA) and its peptide conjugate were tested as potential antibacterial agents in two groups of experiments using a mouse model. In the first group, Escherichia coli mutant strain SM101 with a defective outer membrane was used to induce bacteremia and peritonitis in BALB/c mice by intraperitoneal (i.p.) injection. The resulting bacteremia was fatal within 48 h. A single i.p injection of 5 nmol (or more) of PNA administered 30 min before bacterial challenge significantly reduced the bacterial load in mouse blood. Reductions in serum concentrations of the proinflammatory cytokines tumor necrosis factor alpha, interleukin-1beta (IL-1beta), IL-6, and IL-12 were also observed. PNA treatment was effective in rescuing 100% of infected animals. In the second group, bacteremia in BALB/c mice was induced by i.p. injection of E. coli wild-type strain K-12. The infected mice were treated by a single intravenous injection of peptide-PNA conjugate 30 min after bacterial challenge. Treatment with the peptide-PNA conjugate significantly reduced the K-12 load, with modest reduction in cytokine concentrations. The conjugate treatment was also able to rescue up to 60% of infected animals. This report is the first demonstration of ODNs' antibacterial efficacy in an animal disease model. The ability of PNA and its peptide conjugate to inhibit bacterial growth and to prevent fatal infection demonstrates the potential for this new class of antibacterial agents.

Importance of unusually modified lipid A in Sinorhizobium stress resistance and legume symbiosis

Sinorhizobium meliloti, a legume symbiont and Brucella abortus, a phylogenetically related mammalian pathogen, both require their BacA proteins to establish chronic intracellular infections in their respective hosts. The lipid A molecules of S. meliloti and B. abortus are unusually modified with a very-long-chain fatty acid (VLCFA; C > or = 28) and we discovered that BacA is involved in this unusual modification. This observation raised the possibility that the unusual lipid A modification could be crucial for the chronic infection of both S. meliloti and B. abortus. We investigated this by constructing and characterizing S. meliloti mutants in the lpxXL and acpXL genes, which encode an acyl transferase and acyl carrier protein directly involved in the biosynthesis of VLCFA-modified lipid A. Our analysis revealed that the unusually modified lipid A is important, but not crucial, for S. meliloti chronic infection and that BacA must have an additional function, which in combination with its observed effect on the lipid A in the free-living form of S. meliloti, is essential for the chronic infection. Additionally, we discovered that in the absence of VLCFAs, S. meliloti produces novel pentaacylated lipid A species, modified with unhydroxylated fatty acids, which are important for stress resistance.

A novel approach for over-expression, characterization, and isotopic enrichment of a homogeneous species of acyl carrier protein from Plasmodium falciparum

Acyl carrier protein (ACP) plays a central role in fatty acid biosynthesis by transferring the acyl groups from one enzyme to another for the completion of the fatty acid synthesis cycle. Holo-ACP is the obligatory substrate for the synthesis of acyl-ACPs which act as the carrier and donor for various metabolic reactions. Despite its interactions with numerous proteins in the cell, its mode of interaction is poorly understood. Here, we report the over-expression of PfACP in minimal medium solely in its holo form and in high yield. Expression in minimal media provides a means to isotopically label PfACP for high resolution multi-nuclear and multi-dimensional NMR studies. Indeed, the proton-nitrogen correlated NMR spectrum exhibits very high chemical shift dispersion and resolution. We also show that holo-PfACP thus expressed is amenable to acylation reactions using Escherichia coli acyl-ACP synthetase as well as by standard chemical methods.

A New Modular Polyketide Synthase in the Erythromycin Producer Saccharopolyspora erythraea

A previously unidentified set of genes encoding a modular polyketide synthase (PKS) has been sequenced in Saccharopolyspora erythraea, producer of the antibiotic erythromycin. This new PKS gene cluster (pke) contains four adjacent large open reading frames (ORFs) encoding eight extension modules, flanked by a number of other ORFs which can be plausibly assigned roles in polyketide biosynthesis. Disruption of the pke PKS genes gave S. erythraea mutant JC2::pSBKS6, whose growth characteristics and pattern of secondary metabolite production did not apparently differ from the parent strain under any of the growth conditions tested. However, the pke PKS loading module and individual pke acyltransferase domains were shown to be active when used in engineered hybrid PKSs, making it highly likely that under appropriate conditions these biosynthetic genes are indeed expressed and active, and synthesize a novel polyketide product.

Antisense phosphorodiamidate morpholino oligomer inhibits viability of Escherichia coli in pure culture and in mouse peritonitis

OBJECTIVES

Antisense phosphorodiamidate morpholino oligomers (PMOs) are synthetic DNA mimics that specifically inhibit gene expression in pure cultures of Escherichia coli. Previously, an 11 base PMO targeted to an essential gene (acpP) for phospholipid biosynthesis was shown to inhibit growth of a pure culture of E. coli AS19, which has an abnormally permeable outer membrane. The objectives of experiments in this report are to show that the AcpP PMO significantly inhibits growth of strain SM105, which has a normal, intact outer membrane, both in pure culture and in infected mice.

METHODS

In pure culture, SM105 was grown in rich broth supplemented with 20 muM AcpP PMO, and growth was monitored by optical density and viable cell count. Mice were infected by intraperitoneal injection with a non-lethal inoculum of either E. coli AS19 or SM105. Following infection, mice were treated intraperitoneally with 300 mug of the 11 base antisense PMO targeted to acpP, a scrambled sequence PMO or PBS.

RESULTS

Growth of SM105 was slower and viable cells were significantly reduced by up to 61% in pure cultures supplemented with AcpP PMO compared with untreated cultures or cultures supplemented with a scrambled sequence PMO. A single dose of AcpP PMO reduced peritoneal cfu of E. coli AS19 about 39- to 600-fold compared with controls at 2, 7, 13 and 23 h after treatment. The same PMO significantly reduced cfu of E. coli SM105 75% compared with controls at 12 h after treatment. However, there was no difference in cfu at 2, 7 or 24 h. A second dose at 24 h again reduced SM105 cfu about 10-fold by 48 h post-infection. In other experiments with infected mice, multiple doses of AcpP PMO sustained the approximately 10-fold reduction in SM105 cfu at 6, 12 and 24 h post-infection. Compared with equivalent (micromolar) doses of ampicillin, AcpP PMO was significantly more effective at all time points. Specificity of PMO inhibition was shown in other experiments by treating infected mice with a PMO targeted to a non-essential reporter gene for luciferase. A luciferase-specific PMO reduced both the amount and activity of luciferase to the same extent, whereas scrambled PMO had no effect.

CONCLUSIONS

An 11 base antisense PMO targeted to acpP significantly inhibited viability of a strain of E. coli with a normal, intact outer membrane both in pure culture and in infected mice. Inhibition by PMOs was sequence-specific.

Tandemly Duplicated Acyl Carrier Proteins, Which Increase Polyketide Antibiotic Production, Can Apparently Function Either in Parallel or in Series

Polyketide biosynthesis involves the addition of subunits commonly derived from malonate or methylmalonate to a starter unit such as acetate. Type I polyketide synthases are multifunctional polypeptides that contain one or more modules, each of which normally contains all the enzymatic domains for a single round of extension and modification of the polyketide backbone. Acyl carrier proteins (ACP(s)) hold the extender unit to which the starter or growing chain is added. Normally there is one ACP for each ketosynthase module. However, there are an increasing number of known examples of tandemly repeated ACP domains, whose function is as yet unknown. For the doublet and triplet ACP domains in the biosynthetic pathway for the antibiotic mupirocin from Pseudomonas fluorescens NCIMB10586 we have inactivated ACP domains by inframe deletion and amino acid substitution of the active site serine. By deletion analysis each individual ACP from a cluster can provide a basic but reduced activity for the pathway. In the doublet cluster, substitution analysis indicates that the pathway may follow two parallel routes, one via each of the ACPs, thus increasing overall pathway flow. In the triplet cluster, substitution in ACP5 blocked the pathway. Thus ACP5 appears to be arranged "in series" to ACP6 and ACP7. Thus although both the doublet and triplet clusters increase antibiotic production, the mechanisms by which they do this appear to be different and depend specifically on the biosynthetic stage involved. The function of some ACPs may be determined by their location in the protein rather than absolute enzymic activity.

Dissection of brefeldin A-sensitive and -insensitive steps in apicoplast protein targeting

The apicoplast is a relict plastid found in many apicomplexans, including the pathogens Toxoplasma gondii and Plasmodium falciparum. Nucleus-encoded apicoplast proteins enter the ER, and after cleavage of the signal sequence, are routed to the apicoplast by virtue of a transit peptide, which is subsequently removed. To assess the mechanisms of localization we examined stable transfectants of T. gondii for the localization and processing of various GFP fusion proteins. GFP fusions bearing apicoplast targeting sequences targeted efficiently to the plastid, with no retention in the ER, even when an ER retention/retrieval sequence was added. Incubation with brefeldin A, which blocks ER-to-Golgi trafficking by inhibiting a GTP exchange factor required for retrograde trafficking, blocked the processing of the protein. Surprisingly, it did not affect the immunofluorescence pattern. To avoid the potentially misleading presence of pre-existing GFP fusion protein in the apicoplast, we used a ligand-regulated aggregation system to arrest the GFP fusion protein in the ER prior to trafficking. Upon addition of ligand to promote disaggregation, the fusion protein targeted to the plastid, even in the presence of brefeldin A. Ligand release at 15 degrees C, which blocks trafficking of Golgi-routed proteins, also allowed significant localization to the plastid. Our data indicate that apicoplast proteins can localize to the region of the plastid when Golgi trafficking is inhibited, but suggest that some steps in import or maturation of the proteins may require a brefeldin A-sensitive GTP exchange factor.

Hybrid Nonribosomal Peptide-Polyketide Interfaces in Epothilone Biosynthesis

Epothilone (Epo) D, an antitumor agent currently in clinical trials, is a hybrid natural product produced by the combined action of nonribosomal peptide synthetases (NRPS) and polyketide synthases (PKS). In the epothilone biosynthetic pathway, EpoB, a 165 kDa NRPS is inserted into an otherwise entirely PKS assembly line, forming two hybrid NRPS-PKS interfaces. In light of the terminal linker effect previously identified in PKS, the N- and C-terminal sequences of EpoB were examined for their roles in propagating the incipient natural product. Eight amino acid residues at EpoB C terminus, in which six are positively charged, were found to be a key component of the C-terminal linker effect. A minimal sequence of 56 residues at EpoB N terminus was required for elongating the acetyl group from the acyl carrier protein (ACP) of EpoA to form methylthiazolyl-S-EpoB.

The translation start codon region is sensitive to antisense PNA inhibition in Escherichia coli

Antisense peptide nucleic acids (PNA) can inhibit bacterial gene expression with gene and sequence specificity. Using attached carrier peptides that aid cell permeation, the antisense effects when targeting essential genes are sufficient to prevent growth and even kill bacteria. However, many design uncertainties remain, including the difficult question of target sequence selection. In this study, we synthesized 90 antisense peptide-PNAs to target sequences in a head to tail manner across the entire length of the mRNA encoding beta-lactamase. The results from this scan pointed to the start codon region as most sensitive to inhibition. To confirm and refine the result, a higher-resolution scan was conducted over the start codon region of the beta-lactamase gene and the essential Escherichia coli acpP gene. For both genes, the start codon region, including the Shine-Dalgarno motif, was sensitive, whereas antisense agents targeted outside of this region were largely ineffective. These results are in accord with natural antisense mechanisms, which typically hinder the start codon region, and the sensitivity of this region should hold true for most bacterial genes as well as for other RNase H-independent antisense agents that rely on a steric blocking mechanism. Therefore, although other design parameters are also important, the start codon region in E. coli mRNA is the most reliable target site for antisense PNAs.

Structure of apo acyl carrier protein and a proposal to engineer protein crystallization through metal ions

A topic of current interest is engineering surface mutations in order to improve the success rate of protein crystallization. This report explores the possibility of using metal-ion-mediated crystal-packing interactions to facilitate rational design. Escherichia coli apo acyl carrier protein was chosen as a test case because of its high content of negatively charged carboxylates suitable for metal binding with moderate affinity. The protein was successfully crystallized in the presence of zinc ions. The crystal structure was determined to 1.1 A resolution with MAD phasing using anomalous signals from the co-crystallized Zn(2+) ions. The case study suggested an integrated strategy for crystallization and structure solution of proteins via engineering surface Asp and Glu mutants, crystallizing them in the presence of metal ions such as Zn(2+) and solving the structures using anomalous signals.

Characterization of Cfa1, a monofunctional acyl carrier protein involved in the biosynthesis of the phytotoxin coronatine

Cfa1 was overproduced in Escherichia coli and Pseudomonas syringae, and the degree of 4'-phosphopantetheinylation was determined. The malonyl-coenzyme A:acyl carrier protein transacylase (FabD) of P. syringae was overproduced and shown to catalyze malonylation of Cfa1, suggesting that FabD plays a role in coronatine biosynthesis. Highly purified Cfa1 did not exhibit self-malonylation activity.

Functionality of Wrapping Defects in Soluble Proteins: What Cannot be Kept Dry Must be Conserved

Soluble proteins preserve their structure only if a sufficient number of non-polar groups are clustered around the backbone hydrogen bonds, protecting them from water attack. When these bonds are not properly wrapped or dehydrated intramolecularly, structural integrity can be preserved through binding partnerships. This is because insufficiently wrapped hydrogen bonds are inherently adhesive and become better shielded upon protein-ligand association. Thus, we postulate that deficiently wrapped hydrogen bonds are functionally relevant. Two findings that support this conjecture are: (a) there is a statistically relevant linear correlation between the number of defects in a folding domain and its proteomic connectivity, obtained from large-scale two-hybrid experiments; (b) the residues paired by under-wrapped hydrogen bonds are highly conserved. The high mutational sensitivity of under-wrapped regions can be rationalized, since their structural integrity relies on their propensity to behave as binding sites, in turn, a consequence of their adhesiveness. Thus, the regions in soluble protein structure that cannot be kept dry in water tend to be conserved.

pH-Induced Conformational Transition of H. pylori Acyl Carrier Protein: Insight into the Unfolding of Local Structure

Acyl carrier protein (ACP) is a small acidic protein and its primary structure is highly conserved in various bacterial sources. Despite its small size, it interacts with diverse proteins associated with many biosynthetic pathways. The three-dimensional structure of H. pylori ACP and its structural characteristics were clarified using NMR and CD spectroscopy. H. pylori ACP consists of four helices connected by different sized loops. The helices correspond to residues L3-Q14 (alphaI), S36-G50 (alphaII), D56-E60 (alphaIII), and V65-K76 (alphaVI). The size of each helix differs slightly from that of homologous ACPs. However, H. pylori ACP showed a distinct pH-dependent conformational characteristic: at neutral pH, it adopts a partially unfolded structure, while it has a tight fold at pH 6. The chemical shift perturbation and (1)H-(15)N steady state NOE analysis at both pH 6 and 7 showed that the local change of structural components occurred mainly around loop II, and this change was reflected by the changes of the residues Ile 54 and Asp 56. Examination of the structure showed that the network of Glu 47, Ile 54, Asn 75, and Lys 76 is very important for the structural stability. The pH-dependent folding process shows a kind of cooperativity, since all the residues involved in the conformational transitions are contiguous and in spatial proximity.

In vitro inhibition of the Mycobacterium tuberculosis beta-ketoacyl-acyl carrier protein reductase MabA by isoniazid

The first-line specific antituberculous drug isoniazid inhibits the fatty acid elongation system (FAS) FAS-II involved in the biosynthesis of mycolic acids, which are major lipids of the mycobacterial envelope. The MabA protein that catalyzes the second step of the FAS-II elongation cycle is structurally and functionally related to the in vivo target of isoniazid, InhA, an NADH-dependent enoyl-acyl carrier protein reductase. The present work shows that the NADPH-dependent beta-ketoacyl reduction activity of MabA is efficiently inhibited by isoniazid in vitro by a mechanism similar to that by which isoniazid inhibits InhA activity. It involves the formation of a covalent adduct between Mn(III)-activated isoniazid and the MabA cofactor. Liquid chromatography-mass spectrometry analyses revealed that the isonicotinoyl-NADP adduct has multiple chemical forms in dynamic equilibrium. Both kinetic experiments with isolated forms and purification of the enzyme-ligand complex strongly suggested that the molecules active against MabA activity are the oxidized derivative and a major cyclic form. Spectrofluorimetry showed that the adduct binds to the MabA active site. Modeling of the MabA-adduct complex predicted an interaction between the isonicotinoyl moiety of the inhibitor and Tyr185. This hypothesis was supported by the fact that a higher 50% inhibitory concentration of the adduct was measured for MabA Y185L than for the wild-type enzyme, while both proteins presented similar affinities for NADP(+). The crystal structure of MabA Y185L that was solved showed that the substitution of Tyr185 induced no significant conformational change. The description of the first inhibitor of the beta-ketoacyl reduction step of fatty acid biosynthesis should help in the design of new antituberculous drugs efficient against multidrug-resistant tubercle bacilli.

Cloning, expression, characterization, and interaction of two components of a human mitochondrial fatty acid synthase. Malonyltransferase and acyl carrier protein

The possibility that human cells contain, in addition to the cytosolic type I fatty acid synthase complex, a mitochondrial type II malonyl-CoA-dependent system for the biosynthesis of fatty acids has been examined by cloning, expressing, and characterizing two putative components. Candidate coding sequences for a malonyl-CoA:acyl carrier protein transacylase (malonyltransferase) and its acyl carrier protein substrate, identified by BLAST searches of the human sequence data base, were located on nuclear chromosomes 22 and 16, respectively. The encoded proteins localized exclusively in mitochondria only when the putative N-terminal mitochondrial targeting sequences were present as revealed by confocal microscopy of HeLa cells infected with appropriate green fluorescent protein fusion constructs. The mature, processed forms of the mitochondrial proteins were expressed in Sf9 cells and purified, the acyl carrier protein was converted to the holoform in vitro using purified human phosphopantetheinyltransferase, and the functional interaction of the two proteins was studied. Compared with the dual specificity malonyl/acetyltransferase component of the cytosolic type I fatty acid synthase, the type II mitochondrial counterpart exhibits a relatively narrow substrate specificity for both the acyl donor and acyl carrier protein acceptor. Thus, it forms a covalent acyl-enzyme complex only when incubated with malonyl-CoA and transfers exclusively malonyl moieties to the mitochondrial holoacyl carrier protein. The type II acyl carrier protein from Bacillus subtilis, but not the acyl carrier protein derived from the human cytosolic type I fatty acid synthase, can also function as an acceptor for the mitochondrial transferase. These data provide compelling evidence that human mitochondria contain a malonyl-CoA/acyl carrier protein-dependent fatty acid synthase system, distinct from the type I cytosolic fatty acid synthase, that resembles the type II system present in prokaryotes and plastids. The final products of this system, yet to be identified, may play an important role in mitochondrial function.

Inhibition of gene expression in Escherichia coli by antisense phosphorodiamidate morpholino oligomers

Antisense phosphorodiamidate morpholino oligomers (PMOs) were tested for the ability to inhibit gene expression in Escherichia coli. PMOs targeted to either a myc-luciferase reporter gene product or 16S rRNA did not inhibit luciferase expression or growth. However, in a strain with defective lipopolysaccharide (lpxA mutant), which has a leaky outer membrane, PMOs targeted to the myc-luciferase or acyl carrier protein (acpP) mRNA significantly inhibited their targets in a dose-dependent response. A significant improvement was made by covalently joining the peptide (KFF)(3)KC to the end of PMOs. In strains with an intact outer membrane, (KFF)(3)KC-myc PMO inhibited luciferase expression by 63%. A second (KFF)(3)KC-PMO conjugate targeted to lacI mRNA induced beta-galactosidase in a dose-dependent response. The end of the PMO to which (KFF)(3)KC is attached affected the efficiency of target inhibition but in various ways depending on the PMO. Another peptide-lacI PMO conjugate was synthesized with the cationic peptide CRRRQRRKKR and was found not to induce beta-galactosidase. We conclude that the outer membrane of E. coli inhibits entry of PMOs and that (KFF)(3)KC-PMO conjugates are transported across both membranes and specifically inhibit expression of their genetic targets.

Nonorganellar acyl carrier protein from oleaginous yeast is a homologue of ribosomal protein P2

Acyl carrier protein (ACP) is responsible for carrying the growing fatty acid chain from one enzyme active site to the next during fatty acid biosynthesis. Here we report the identification, purification, immunocytochemical localization, and cloning of ACP from the oleaginous yeast, Rhodotorula glutinis. The soluble fraction of this organism can synthesize triacylglycerol and is able to accept the acyl group from acyl-ACP for the synthesis. The ACP, cloned from the system, showed a significant similarity with ribosomal protein P2. Expression and characterization of the recombinant protein showed that the ACP was acylated in vitro. The recombinant protein was post-translationally modified, since it was observed in [14C]beta-alanine labeling and matrix-assisted laser desorption mass spectroscopic analysis. Site-directed mutants were generated to identify a serine residue responsible for phosphopantetheinylation and found that mutation of serine 59 to alanine abrogated the fatty acylation ability of the protein. These results demonstrate that a novel modification of ribosomal protein P2 allows it to act as an acyl carrier protein and participate in acylation reactions.

Differential expression of fatty acid synthase genes, Acl, Fat and Kas, in Capsicum fruit

The biosynthesis of capsaicinoids in the placenta of chilli fruit is modelled to require components of the fatty acid synthase (FAS) complex. Three candidate genes for subunits in this complex, Kas, Acl, and Fat, isolated based on differential expression, were characterized. Transcription of these three genes was placental-specific and RNA abundance was positively correlated with degree of pungency. Kas and Acl were mapped to linkage group 1 and Fat to linkage group 6. None of the genes is linked to the pungency locus, C, on linkage group 2. KAS accumulation was positively correlated with pungency. Western blots of placental extracts and histological sections both demonstrated that the accumulation of this enzyme was correlated with fruit pungency and KAS was immunolocalized to the expected cell layer, the placental epidermis. Enzyme activity of the recombinant form of the placental-specific KAS was confirmed using crude cell extracts. These FAS components are fruit-specific members of their respective gene families. These genes are predicted to be associated with Capsicum fruit traits, for example, capsaicinoid biosynthesis or fatty acid biosynthesis necessary for placental development.

Ophthalmic manifestations of congenital disorder of glycosylation type 1a

PURPOSE

To present the ophthalmic manifestations of patients with congenital disorder of glycosylation type Ia (CDG-Ia) due to the frequent R141H/F119L PMM2 genotype.

METHODS

Ophthalmic records of 23 patients (age: 10 months to 20 years) were evaluated. They had had at least one ophthalmic reexamination.

RESULTS

Measurements of refractive error showed that 18 patients were myopic, two were hypermetropic, and three could not be measured. Serial measurements in 12 patients indicated a progression towards myopia of 0.80 diopters (D) per year. Congenital esotropia and delayed visual maturation (DVM) were consistent findings. Two children developed good visual acuity (VA), 16 had low vision, and five were legally blind. Pallor of the optic disc was noted in five patients. Electroretinography (ERG) performed in nine patients showed reduced rod responses, while cone responses were only slightly reduced.

CONCLUSIONS

The present study illustrates the difficulties in examining severely disabled children. Consistent ophthalmic manifestations of CDG-Ia patients due to the R141H/F119L genotype were congenital esotropia, DVM, and a reduced rod response in ERG-examined patients. The vast majority of patients had reduced VA and developed myopia. We speculate that there is a relationship between the glycosylation defect in CDG-Ia and the development of myopia. We recommend that CDG-Ia patients be followed annually by an ophthalmologist.

Expression of antisense acyl carrier protein-4 reduces lipid content in Arabidopsis leaf tissue

Arabidopsis plants were transformed with acyl carrier protein (ACP)-4 in antisense conformation driven by the cauliflower mosaic virus 35S promoter. It was hypothesized that reduction of ACP4 in leaf tissue would result in a reduction in lipid biosynthesis and, in addition, affect fatty acid composition and leaf physiology. Several transgenic lines have been generated with reduced ACP4 protein in leaf tissue. Dramatic reductions in ACP4 resulted in a reduction of leaf lipid content (22%-60%) based on fresh leaf weight and a bleached appearance and reduced photosynthetic efficiency. In addition, a decrease in 16:3 as a percentage of the total fatty acid composition was noted. There were no changes in leaf lipid class distribution; however, there was a decrease in the relative amount of 16:3 in monogalactosyldiacylglycerol. These results suggest that ACP4 plays a major role in the biosynthesis of fatty acids for chloroplast membrane development. Alterations in the ACP isoform profile of Arabidopsis leaf also appear to alter the flow of fatty acids between the prokaryotic and eukaryotic pathways for assembly of galactolipids. However, it has not yet been determined if the changes in fatty acid composition are due to changes in the profile of ACP isoforms, or if they are actually a reaction to a reduction in fatty acid precursors.

Sinorhizobium meliloti acpXL mutant lacks the C28 hydroxylated fatty acid moiety of lipid A and does not express a slow migrating form of lipopolysaccharide

Lipid A is the hydrophobic anchor of lipopolysaccharide (LPS) in the outer membrane of Gram-negative bacteria. Lipid A of all Rhizobiaceae is acylated with a long fatty acid chain, 27-hydroxyoctacosanoic acid. Biosynthesis of this long acyl substitution requires a special acyl carrier protein, AcpXL, which serves as a donor of C28 (omega-1)-hydroxylated fatty acid for acylation of rhizobial lipid A (Brozek, K.A., Carlson, R.W., and Raetz, C. R. (1996) J. Biol. Chem. 271, 32126-32136). To determine the biological function of the C28 acylation of lipid A, we constructed an acpXL mutant of Sinorhizobium meliloti strain 1021. Gas-liquid chromatography and mass spectrometry analysis of the fatty acid composition showed that the acpXL mutation indeed blocked C28 acylation of lipid A. SDS-PAGE analysis of acpXL mutant LPS revealed only a fast migrating band, rough LPS, whereas the parental strain 1021 manifested both rough and smooth LPS. Regardless of this, the LPS of parental and mutant strains had a similar sugar composition and exposed the same antigenic epitopes, implying that different electrophoretic profiles might account for different aggregation properties of LPS molecules with and without a long acyl chain. The acpXL mutant of strain 1021 displayed sensitivity to deoxycholate, delayed nodulation of Medicago sativa, and a reduced competitive ability. However, nodules elicited by this mutant on roots of M. sativa and Medicago truncatula had a normal morphology and fixed nitrogen. Thus, the C28 fatty acid moiety of lipid A is not crucial, but it is beneficial for establishing an effective symbiosis with host plants. acpXL lies upstream from a cluster of five genes, including msbB (lpxXL), which might be also involved in biosynthesis and transfer of the C28 fatty acid to the lipid A precursor.