Occurrence of two 5-aminolevulinate biosynthetic pathways in Streptomyces nodosus subsp. asukaensis is linked with the production of asukamycin

CLPP-Null Eukaryotes with Excess Heme Biosynthesis Show Reduced L-arginine Levels, Probably via CLPX-Mediated OAT Activation

The serine peptidase CLPP is conserved among bacteria, chloroplasts, and mitochondria. In humans and mice, its loss causes Perrault syndrome, which presents with growth deficits, infertility, deafness, and ataxia. In the filamentous fungus Podospora anserina, CLPP loss leads to longevity. CLPP substrates are selected by CLPX, an AAA+ unfoldase. CLPX is known to target delta-aminolevulinic acid synthase (ALAS) to promote pyridoxal phosphate (PLP) binding. CLPX may also influence cofactor association with other enzymes. Here, the evaluation of P. anserina metabolomics highlighted a reduction in arginine/histidine levels. In Mus musculus cerebellum, reductions in arginine/histidine and citrulline occurred with a concomitant accumulation of the heme precursor protoporphyrin IX. This suggests that the increased biosynthesis of 5-carbon (C5) chain deltaALA consumes not only C4 succinyl-CoA and C1 glycine but also specific C5 delta amino acids. As enzymes responsible for these effects, the elevated abundance of CLPX and ALAS is paralleled by increased OAT (PLP-dependent, ornithine delta-aminotransferase) levels. Possibly as a consequence of altered C1 metabolism, the proteome profiles of P. anserina CLPP-null cells showed strong accumulation of a methyltransferase and two mitoribosomal large subunit factors. The reduced histidine levels may explain the previously observed metal interaction problems. As the main nitrogen-storing metabolite, a deficiency in arginine would affect the urea cycle and polyamine synthesis. Supplementation of arginine and histidine might rescue the growth deficits of CLPP-mutant patients.

Acyltransferase Domain Exchange between Two Independent Type I Polyketide Synthases in the Same Producer Strain of Macrolide Antibiotics

Streptomyces graminofaciens A-8890 produces two macrolide antibiotics, FD-891 and virustomycin A, both of which show significant biological activity. In this study, we identified the virustomycin A biosynthetic gene cluster, which encodes type I polyketide synthases (PKSs), ethylmalonyl-CoA biosynthetic enzymes, methoxymalony-acyl carrier protein biosynthetic enzymes, and post-PKS modification enzymes. Next, we demonstrated that the acyltransferase domain can be exchanged between the Vsm PKSs and the PKSs involved in FD-891 biosynthesis (Gfs PKSs), without any supply problems of the unique extender units. We exchanged the malonyltransferase domain in the loading module of Gfs PKS with the ethylmalonyltransferase domain and the methoxymalonyltransferase domain of Vsm PKSs. Consequently, the expected two-carbon-elongated analog 26-ethyl-FD-891 was successfully produced with a titer comparable to FD-891 production by the wild type; however, exchange with the methoxymalonyltransferase domain did not produce any FD-891 analogs. Furthermore, 26-ethyl-FD-891 showed potent cytotoxic activity against HeLa cells, like natural FD-891.

A secondary metabolic enzyme functioned as an evolutionary seed of a primary metabolic enzyme

The antibiotic alaremycin has a structure that resembles that of 5-aminolevulinic acid (ALA), a universal precursor of porphyrins, and inhibits porphyrin biosynthesis. Genome sequencing of the alaremycin-producing bacterial strain and enzymatic analysis revealed that the first step of alaremcyin biosynthesis is catalysed by the enzyme, AlmA, which exhibits a high degree of similarity to 5-aminolevulinate synthase (ALAS) expressed by animals, protozoa, fungi and α-proteobacteria. Site-directed mutagenesis of AlmA revealed that the substitution of two amino acids residues around the substrate binding pocket transformed its substrate specificity from that of alaremycin precursor synthesis to ALA synthesis. To estimate the evolutionary trajectory of AlmA and ALAS, we performed an ancestral sequence reconstitution analysis based on a phylogenetic tree of AlmA and ALAS. The reconstructed common ancestral enzyme of AlmA and ALAS exhibited alaremycin precursor synthetic activity, rather than ALA synthetic activity. These results suggest that ALAS evolved from an AlmA-like enzyme. We propose a new evolutionary hypothesis in which a non-essential secondary metabolic enzyme acts as an 'evolutionary seed' to generate an essential primary metabolic enzyme.

Proteomic analysis of a hom-disrupted, cephamycin C overproducing Streptomyces clavuligerus

BACKGROUND

Streptomyces clavuligerus is prolific producer of cephamycin C, a medically important antibiotic. In our former study, cephamycin C titer was 2-fold improved by disrupting homoserine dehydrogenase (hom) gene of aspartate pahway in Streptomyces clavuligerus NRRL 3585.

OBJECTIVE

In this article, we aimed to provide a comprehensive understanding at the proteome level on potential complex metabolic changes as a consequence of hom disruption in Streptomyces clavuligerus AK39.

METHODS

A comparative proteomics study was carried out between the wild type and its hom disrupted AK39 strain by 2 Dimensional Electrophoresis-Matrix Assisted Laser Desorption and Ionization Time-Of-Flight Mass Spectrometry (2DE MALDI-TOF/MS) and Nanoscale Liquid Chromatography- Tandem Mass Spectrometry (nanoLC-MS/MS) analyses. Clusters of Orthologous Groups (COG) database was used to determine the functional categories of the proteins. The theoretical pI and Mw values of the proteins were calculated using Expasy pI/Mw tool.

RESULTS

"Hypothetical/Unknown" and "Secondary Metabolism" were the most prominent categories of the differentially expressed proteins. Upto 8.7-fold increased level of the positive regulator CcaR was a key finding since CcaR was shown to bind to cefF promoter thereby direcly controlling its expression. Consistently, CeaS2, the first enzyme of CA biosynthetic pathway, was 3.3- fold elevated. There were also many underrepresented proteins associated with the biosynthesis of several Non-Ribosomal Peptide Synthases (NRPSs), clavams, hybrid NRPS/Polyketide synthases (PKSs) and tunicamycin. The most conspicuously underrepresented protein of amino acid metabolism was 4-Hydroxyphenylpyruvate dioxygenase (HppD) acting in tyrosine catabolism. The levels of a Two Component System (TCS) response regulator containing a CheY-like receiver domain and an HTH DNA-binding domain as well as DNA-binding protein HU were elevated while a TetR-family transcriptional regulator was underexpressed.

CONCLUSION

The results obtained herein will aid in finding out new targets for further improvement of cephamycin C production in Streptomyces clavuligerus.

Inhibition of Pro-Inflammatory Cytokines by Metabolites of Streptomycetes-A Potential Alternative to Current Anti-Inflammatory Drugs?

Current treatment of chronic diseases includes, among others, application of cytokines, monoclonal antibodies, cellular therapies, and immunostimulants. As all the underlying mechanisms of a particular diseases are not always fully clarified, treatment can be inefficient and associated with various, sometimes serious, side effects. Small secondary metabolites produced by various microbes represent an attractive alternative as future anti-inflammatory drug leads. Compared to current drugs, they are cheaper, can often be administered orally, but still can keep a high target-specificity. Some compounds produced by actinomycetes or fungi have already been used as immunomodulators—tacrolimus, sirolimus, and cyclosporine. This work documents strong anti-inflammatory features of another secondary metabolite of streptomycetes—manumycin-type polyketides. We compared the effect of four related compounds: manumycin A, manumycin B, asukamycin, and colabomycin E on activation and survival of human monocyte/macrophage cell line THP-1. The anti-cancer effect of manucycine A has been demonstrated; the immunomodulatory capacities of manumycin A are obvious when using micromolar concentrations. The application of all four compounds in 0.25–5 μM concentrations leads to efficient, concentration-dependent inhibition of IL-1β and TNF expression in THP-1 upon LPS stimulation, while the three latter compounds show a significantly lower pro-apoptotic effect than manumycin A. We have demonstrated the anti-inflammatory capacity of selected manumycin-type polyketides.

Rational Design of Hybrid Natural Products by Utilizing the Promiscuity of an Amide Synthetase

WS9326A and annimycin are produced by Streptomyces asterosporus DSM 41452. WS9326A is a nonribosomal peptide synthetase-(NRPS-) derived depsipeptide containing a cinnamoyl moiety, while annimycin is a linear polyketide bearing a 2-amino-3-hydroxycyclopent-2-enone (C₅N) group. Both gene clusters have been sequenced and annotated. In this study, we show that the amide synthetase Ann1, responsible for attaching the C₅N unit during annimycin biosynthesis, has the ability to catalyze fortuitous side reactions to polyenoic acids in addition to its main reaction. Novel compounds were generated by feeding experiments and in vitro studies. We also rationally designed a hybrid natural product consisting of the cinnamoyl moiety of WS9326A and the C₅N moiety of annimycin by creating a mutant of S. asterosporus that retains genes encoding biosynthesis of the C₅N unit of annimycin and the cinnamoyl group of WS9326A. The promiscuity of Ann1 also proved useful for trapping compounds that arise from acyl-ACP intermediates, which occur in the biosynthesis of the cinnamoyl moiety of WS9326A, by hydrolysis. In this pathway, we postulate that sas27 and sas28 genes are involved in the biosynthesis of the cinnamoyl moiety in WS9326A.

Investigating the bifunctionality of cyclizing and "classical" 5-aminolevulinate synthases

The precursor to all tetrapyrroles is 5-aminolevulinic acid, which is made either via the condensation of glycine and succinyl-CoA catalyzed by an ALA synthase (the C4 or Shemin pathway) or by a pathway that uses glutamyl-tRNA as a precursor and involves other enzymes (the C5 pathway). Certain ALA synthases also catalyze the cyclization of ALA-CoA to form 2-amino-3-hydroxycyclopent-2-en-1-one. Organisms with synthases that possess this second activity nevertheless rely upon the C5 pathway to supply ALA for tetrapyrrole biosynthesis. The C₅ N units are components of a variety of secondary metabolites. Here, we show that an ALA synthase used exclusively for tetrapyrrole biosynthesis is also capable of catalyzing the cyclization reaction, albeit at much lower efficiency than the dedicated cyclases. Two absolutely conserved serines present in all known ALA-CoA cyclases are threonines in all known ALA synthases, suggesting they could be important in distinguishing the functions of these enzymes. We found that purified mutant proteins having single and double substitutions of the conserved residues are not improved in their respective alternate activities; rather, they are worse. Protein structural modeling and amino acid sequence alignments were explored within the context of what is known about the reaction mechanisms of these two different types of enzymes to consider what other features are important for the two activities.

Role of two 5-aminolevulinic acid biosynthetic pathways in heme and secondary metabolite biosynthesis in Amycolatopsis orientalis

Analysis of the Amycolatopsis orientalis genome revealed that two genes, hemA1 and hemA2, belonging to divergent pathways, were involved in the biosynthesis of 5-aminolevulinic acid. The roles of hemA1 and hemA2 were elucidated via genetic manipulation and metabolite analysis. The disruption of hemA1, encoding the glutamyl-tRNA^Glu reductase of the C₅ pathway, was essential for cell growth and is used for heme synthesis. Overexpression of hemA1 resulted in elevated vancomycin and ECO-0501 production in Amycolatopsis orientalis, and it was also effective in increasing the production of daptomycin and natamycin in other Streptomycetes. The disruption of hemA2 indicated that it encodes the 5-aminolevulinic acid synthase of the Shemin pathway, serving as a key enzyme for the synthesis of the precursor aminohydroxycyclopentenone unit of ECO-0501. However, hemA2 disruption could not be complemented by the addition of 5-aminolevulinic acid or by the expression of hemA2 outside of the ECO-0501 gene cluster. The synthesis of ECO-0501 was only restored by the insertion of hemA2 at its original locus. The hemA2 gene could partly complement the hemA1 deficiency. Overexpression of hemA1, a key gene from the heme biosynthetic pathway, is proposed here as a new approach to improve the production of secondary metabolites in bacteria, whereas hemA2 plays different roles depending on its pattern of expression.

Evolution of cyclizing 5-aminolevulinate synthases in the biosynthesis of actinomycete secondary metabolites: outcomes for genetic screening techniques

A combined approach, comprising PCR screening and genome mining, was used to unravel the diversity and phylogeny of genes encoding 5-aminolevulinic acid synthases (ALASs, hemA gene products) in streptomycetes-related strains. In actinomycetes, these genes were believed to be directly connected with the production of secondary metabolites carrying the C5N unit, 2-amino-3-hydroxycyclopent-2-enone, with biological activities making them attractive for future use in medicine and agriculture. Unlike "classical" primary metabolism ALAS, the C5N unit-forming cyclizing ALAS (cALAS) catalyses intramolecular cyclization of nascent 5-aminolevulinate. Specific amino acid sequence changes can be traced by comparison of "classical" ALASs against cALASs. PCR screening revealed 226 hemA gene-carrying strains from 1,500 tested, with 87% putatively encoding cALAS. Phylogenetic analysis of the hemA homologs revealed strain clustering according to putative type of metabolic product, which could be used to select producers of specific C5N compound classes. Supporting information was acquired through analysis of actinomycete genomic sequence data available in GenBank and further genetic or metabolic characterization of selected strains. Comparison of 16S rRNA taxonomic identification and BOX-PCR profiles provided evidence for numerous horizontal gene transfers of biosynthetic genes or gene clusters within actinomycete populations and even from non-actinomycete organisms. Our results underline the importance of environmental and evolutionary data in the design of efficient techniques for identification of novel producers.

Biosynthesis of colabomycin E, a new manumycin-family metabolite, involves an unusual chain-length factor

Colabomycin E is a new member of the manumycin-type metabolites produced by the strain Streptomyces aureus SOK1/5-04 and identified by genetic screening from a library of streptomycete strains. The structures of colabomycin E and accompanying congeners were resolved. The entire biosynthetic gene cluster was cloned and expressed in Streptomyces lividans. Bioinformatic analysis and mutagenic studies identified components of the biosynthetic pathway that are involved in the formation of both polyketide chains. Recombinant polyketide synthases (PKSs) assembled from the components of colabomycin E and asukamycin biosynthetic routes catalyzing the biosynthesis of "lower" carbon chains were constructed and expressed in S. aureus SOK1/5-04 ΔcolC11-14 deletion mutant. Analysis of the metabolites produced by recombinant strains provided evidence that in both biosynthetic pathways the length of the lower carbon chain is controlled by an unusual chain-length factor supporting biosynthesis either of a triketide in asukamycin or of a tetraketide in colabomycin E. Biological activity assays indicated that colabomycin E significantly inhibited IL-1β release from THP-1 cells and might thus potentially act as an anti-inflammatory agent.

The pleiotropic effect of WD-40 domain containing proteins on cellular differentiation and production of secondary metabolites in Streptomyces coelicolor

The genome of Streptomyces coelicolor encodes six potential WD-40 genes. Two of them, the wdpB (SCO5953) and the wdpC (SCO4422) genes, were studied to determine their function. Deletion of the wdpB gene resulted in a considerable decrease of aerial hyphae formation, leading to a conditionally bald phenotype, and reduced undecylprodigiosin production. In addition, the aerial hyphae of the ΔwdpB mutant strain were unusually branched and showed the signs of irregular septation and precocious lysis. Disruption of wdpC resulted in the reduction of undecylprodigiosin and delayed actinorhodin production. The ΔwdpC mutant strain showed precocious lysis of hyphae and delayed sporulation without typical curling of aerial hyphae in the early sporulation stage. The whole-genome transcriptome analysis revealed that deletion of wdpB affects the expression of genes involved in aerial hyphae differentiation, sporulation and secondary metabolites production. Deletion of wdpC caused downregulation of several gene clusters encoding secondary metabolites. Both the wdp genes seem to possess transcriptional autoregulatory function. Overexpression and genetic complementation studies confirmed the observed phenotype of both mutants. The results obtained suggest that both genes studied have a pleiotropic effect on physiological and morphological differentiation.

Effect of starter unit availability on the spectrum of manumycin-type metabolites produced by Streptomyces nodosus ssp. asukaensis

AIMS

Production of minor asukamycin congeners and its new derivatives by combination of targeted genetic manipulations with specific precursor feeding in the producer of asukamycin, Streptomyces nodosus ssp. asukaensis.

METHODS AND RESULTS

Structural variations of manumycins lie only in the diverse initiation of the 'upper' polyketide chain. Inactivation of the gene involved in the biosynthesis of cyclohexanecarboxylic acid (CHC) turned off the production of asukamycin in the mutant strain and allowed an increased production of other manumycins with the branched end of the upper chain. The ratio of produced metabolites was further affected by specific precursor feeding. Precursor-directed biosynthesis of a new asukamycin analogue (asukamycin I, 28%) with linear initiation of the upper chain was achieved by feeding norleucine to the mutant strain. Another asukamycin analogue with the unbranched upper chain (asukamycin H, 14%) was formed by the CHC-deficient strain expressing a heterologous gene putatively involved in the formation of the n-butyryl-CoA starter unit of manumycin A.

CONCLUSIONS

Combination of the described techniques proved to be an efficient tool for the biosynthesis of minor or novel manumycins.

SIGNIFICANCE AND IMPACT OF THE STUDY

Production of two novel asukamycin derivatives, asukamycins H and I, was achieved. Variations appeared in the upper polyketide chain, the major determinant of enzyme-inhibitory features of manumycins, affecting their cancerostatic or anti-inflammatory features.

Sequence evidence for the presence of two tetrapyrrole pathways in Euglena gracilis

Genes encoding enzymes of the tetrapyrrole biosynthetic pathway were searched within Euglena gracilis EST databases and 454 genome reads and their 5' end regions were sequenced when not available. Phylogenetic analyses and protein localization predictions support the hypothesis concerning the presence of two separated tetrapyrrole pathways in E. gracilis. One of these pathways resembles the heme synthesis in primarily heterotrophic eukaryotes and was presumably present in the host cell prior to secondary endosymbiosis with a green alga. The second pathway is similar to the plastid-localized tetrapyrrole syntheses in plants and photosynthetic algae. It appears to be localized to the secondary plastid, presumably derived from an algal endosymbiont and probably serves only for the production of plastidial heme and chlorophyll. Thus, E. gracilis represents an evolutionary intermediate in a metabolic transformation of a primary heterotroph to a photoautotroph through secondary endosymbiosis. We propose here that the tetrapyrrole pathway serves as a highly informative marker for the evolution of plastids and plays a crucial role in the loss of plastids.

Molecular enzymology of 5-aminolevulinate synthase, the gatekeeper of heme biosynthesis

Pyridoxal-5'-phosphate (PLP) is an obligatory cofactor for the homodimeric mitochondrial enzyme 5-aminolevulinate synthase (ALAS), which controls metabolic flux into the porphyrin biosynthetic pathway in animals, fungi, and the α-subclass of proteobacteria. Recent work has provided an explanation for how this enzyme can utilize PLP to catalyze the mechanistically unusual cleavage of not one but two substrate amino acid α-carbon bonds, without violating the theory of stereoelectronic control of PLP reaction-type specificity. Ironically, the complex chemistry is kinetically insignificant, and it is the movement of an active site loop that defines k(cat) and ultimately, the rate of porphyrin biosynthesis. The kinetic behavior of the enzyme is consistent with an equilibrium ordered induced-fit mechanism wherein glycine must bind first and a portion of the intrinsic binding energy with succinyl-Coenzyme A is then utilized to perturb the enzyme conformational equilibrium towards a closed state wherein catalysis occurs. Return to the open conformation, coincident with ALA dissociation, is the slowest step of the reaction cycle. A diverse variety of loop mutations have been associated with hyperactivity, suggesting the enzyme has evolved to be purposefully slow, perhaps as a means to allow for rapid up-regulation of activity in response to an as yet undiscovered allosteric type effector. Recently it was discovered that human erythroid ALAS mutations can be associated with two very different diseases. Mutations that down-regulate activity can lead to X-linked sideroblastic anemia, which is characterized by abnormally high iron levels in mitochondria, while mutations that up-regulate activity are associated with X-linked dominant protoporphyria, which in contrast is phenotypically identified by abnormally high porphyrin levels. This article is part of a Special Issue entitled: Pyridoxal Phosphate Enzymology.

Moenomycin family antibiotics: chemical synthesis, biosynthesis, and biological activity

The review (with 214 references cited) is devoted to moenomycins, the only known group of antibiotics that directly inhibit bacterial peptidoglycan glycosytransferases. Naturally occurring moenomycins and chemical and biological approaches to their derivatives are described. The biological properties of moenomycins and plausible mechanisms of bacterial resistance to them are also covered here, portraying a complete picture of the chemistry and biology of these fascinating natural products

A three enzyme pathway for 2-amino-3-hydroxycyclopent-2-enone formation and incorporation in natural product biosynthesis

A number of natural products contain a 2-amino-3-hydroxycyclopent-2-enone five membered ring, termed C(5)N, which is condensed via an amide linkage to a variety of polyketide-derived polyenoic acid scaffolds. Bacterial genome mining indicates three tandem ORFs that may be involved in C(5)N formation and subsequent installation in amide linkages. We show that the protein products of three tandem ORFs (ORF33-35) from the ECO-02301 biosynthetic gene cluster in Streptomyces aizunenesis NRRL-B-11277, when purified from Escherichia coli, demonstrate the requisite enzyme activities for C(5)N formation and amide ligation. First, succinyl-CoA and glycine are condensed to generate 5-aminolevulinate (ALA) by a dedicated PLP-dependent ALA synthase (ORF34). Then ALA is converted to ALA-CoA through an ALA-AMP intermediate by an acyl-CoA ligase (ORF35). ALA-CoA is unstable and has a half-life of approximately 10 min under incubation conditions for off-pathway cyclization to 2,5-piperidinedione. The ALA synthase can compete with the nonenzymatic decomposition route and act in a novel second transformation, cyclizing ALA-CoA to C(5)N. C(5)N is then a substrate for the third enzyme, an ATP-dependent amide synthetase (ORF33). Using octatrienoic acid as a mimic of the C(56) polyenoic acid scaffold of ECO-02301, formation of the octatrienyl-C(5)N product was observed. This three enzyme pathway is likely the general route to the C(5)N ring system in other natural products, including the antibiotic moenomycin.

Biochemical and genetic insights into asukamycin biosynthesis

Asukamycin, a member of the manumycin family metabolites, is an antimicrobial and potential antitumor agent isolated from Streptomyces nodosus subsp. asukaensis. The entire asukamycin biosynthetic gene cluster was cloned, assembled, and expressed heterologously in Streptomyces lividans. Bioinformatic analysis and mutagenesis studies elucidated the biosynthetic pathway at the genetic and biochemical level. Four gene sets, asuA-D, govern the formation and assembly of the asukamycin building blocks: a 3-amino-4-hydroxybenzoic acid core component, a cyclohexane ring, two triene polyketide chains, and a 2-amino-3-hydroxycyclopent-2-enone moiety to form the intermediate protoasukamycin. AsuE1 and AsuE2 catalyze the conversion of protoasukamycin to 4-hydroxyprotoasukamycin, which is epoxidized at C5-C6 by AsuE3 to the final product, asukamycin. Branched acyl CoA starter units, derived from Val, Leu, and Ile, can be incorporated by the actions of the polyketide synthase III (KSIII) AsuC3/C4 as well as the cellular fatty acid synthase FabH to produce the asukamycin congeners A2-A7. In addition, the type II thioesterase AsuC15 limits the cellular level of omega-cyclohexyl fatty acids and likely maintains homeostasis of the cellular membrane.

The tetrapyrrole biosynthetic pathway and its regulation in Rhodobacter capsulatus

The purple anoxygenic photosynthetic bacterium Rhodobacter capsulatus is capable of growing in aerobic or anaerobic conditions, in the dark or using light, etc. Achieving versatile metabolic adaptations from respiration to photosynthesis requires the use of tetrapyrroles such as heme and bacteriochlorophyll, in order to carry oxygen, to transfer electrons, and to harvest light energy. A third tetrapyrrole, cobalamin (vitamin B(12)), is synthesized and used as a cofactor for many enzymes. Heme, bacteriochlorophyll, and vitamin B(12) constitute three major end products of the tetrapyrrole biosynthetic pathway in purple bacteria. Their respective synthesis involves a plethora of enzymes, several that have been characterized and several that are uncharacterized, as described in this review. To respond to changes in metabolic requirements, the pathway undergoes complex regulation to direct the flow of tetrapyrrole intermediates into a specific branch(s) at the expense of other branches of the pathway. Transcriptional regulation of the tetrapyrrole synthesizing enzymes by redox conditions and pathway intermediates is reviewed. In addition, we discuss the involvement of several transcription factors (RegA, CrtJ, FnrL, AerR, HbrL, Irr) as well as the role of riboswitches. Finally, the interdependence of the tetrapyrrole branches on each other synthesis is discussed.

Structure of the heme biosynthetic Pseudomonas aeruginosa porphobilinogen synthase in complex with the antibiotic alaremycin

The recently discovered antibacterial compound alaremycin, produced by Streptomyces sp. A012304, structurally closely resembles 5-aminolevulinic acid, the substrate of porphobilinogen synthase. During the initial steps of heme biosynthesis, two molecules of 5-aminolevulinic acid are asymmetrically condensed to porphobilinogen. Alaremycin was found to efficiently inhibit the growth of both Gram-negative and Gram-positive bacteria. Using the newly created heme-permeable strain Escherichia coli CSA1, we are able to uncouple heme biosynthesis from bacterial growth and demonstrate that alaremycin targets the heme biosynthetic pathway. Further studies focused on the activity of alaremycin against the opportunistic pathogenic bacterium Pseudomonas aeruginosa. The MIC of alaremycin was determined to be 12 mM. Alaremycin was identified as a direct inhibitor of recombinant purified P. aeruginosa porphobilinogen synthase and had a K(i) of 1.33 mM. To understand the molecular basis of alaremycin's antibiotic activity at the atomic level, the P. aeruginosa porphobilinogen synthase was cocrystallized with the alaremycin. At 1.75-A resolution, the crystal structure reveals that the antibiotic efficiently blocks the active site of porphobilinogen synthase. The antibiotic binds as a reduced derivative of 5-acetamido-4-oxo-5-hexenoic acid. The corresponding methyl group is, however, not coordinated by any amino acid residues of the active site, excluding its functional relevance for alaremycin inhibition. Alaremycin is covalently bound by the catalytically important active-site lysine residue 260 and is tightly coordinated by several active-site amino acids. Our data provide a solid structural basis to further improve the activity of alaremycin for rational drug design. Potential approaches are discussed.

Complete characterization of the seventeen step moenomycin biosynthetic pathway

The moenomycins are phosphoglycolipid antibiotics produced by Streptomyces ghanaensis and related organisms. The phosphoglycolipids are the only known active site inhibitors of the peptidoglycan glycosyltransferases, an important family of enzymes involved in the biosynthesis of the bacterial cell wall. Although these natural products have exceptionally potent antibiotic activity, pharmacokinetic limitations have precluded their clinical use. We previously identified the moenomycin biosynthetic gene cluster in order to facilitate biosynthetic approaches to new derivatives. Here, we report a comprehensive set of genetic and enzymatic experiments that establish functions for the 17 moenomycin biosynthetic genes involved in the synthesis of moenomycin and variants. These studies reveal the order of assembly of the full molecular scaffold and define a subset of seven genes involved in the synthesis of bioactive analogues. This work will enable both in vitro and fermentation-based reconstitution of phosphoglycolipid scaffolds so that chemoenzymatic approaches to novel analogues can be explored.

The biochemistry of heme biosynthesis

Heme is an integral part of proteins involved in multiple electron transport chains for energy recovery found in almost all forms of life. Moreover, heme is a cofactor of enzymes including catalases, peroxidases, cytochromes of the P(450) class and part of sensor molecules. Here the step-by-step biosynthesis of heme including involved enzymes, their mechanisms and detrimental health consequences caused by their failure are described. Unusual and challenging biochemistry including tRNA-dependent reactions, radical SAM enzymes and substrate derived cofactors are reported.

A streamlined metabolic pathway for the biosynthesis of moenomycin A

Moenomycin A (MmA) is a member of the phosphoglycolipid family of antibiotics, which are the only natural products known to directly target the extracellular peptidoglycan glycosyltransferases involved in bacterial cell wall biosynthesis. The structural and biological uniqueness of MmA make it an attractive starting point for the development of new antibacterial drugs. In order both to elucidate the biosynthesis of this unusual compound and to develop tools to manipulate its structure, we have identified the MmA biosynthetic genes in Streptomyces ghanaensis (ATCC14672). We show via heterologous expression of a subset of moe genes that the economy of the MmA pathway is enabled through the use of sugar-nucleotide and isoprenoid building blocks derived from primary metabolism. The work reported lays the foundation for genetic engineering of MmA biosynthesis to produce novel derivatives.