In 2010 there were more than 200 million cases of malaria, and at least 655,000 deaths 1 . The World Health Organization has recommended artemisinin-based combination therapies (ACTs) for the treatment of uncomplicated malaria caused by the parasite Plasmodium falciparum. Artemisinin is a sesquiterpene endoperoxide with potent antimalarial properties, produced by the plant Artemisia annua. However, the supply of plant-derived artemisinin is unstable, resulting in shortages and price fluctuations, complicating production planning by ACT manufacturers 2 . A stable source of affordable artemisinin is required. Here we use synthetic biology to develop strains of Saccharomyces cerevisiae (baker's yeast) for high-yielding biological production of artemisinic acid, a precursor of artemisinin. Previous attempts to produce commercially relevant concentrations of artemisinic acid were unsuccessful, allowing production of only 1.6 grams per litre of artemisinic acid 3 . Here we demonstrate the complete biosynthetic pathway, including the discovery of a plant dehydrogenase and a second cytochrome that provide an efficient biosynthetic route to artemisinic acid, with fermentation titres of 25 grams per litre of artemisinic acid. Furthermore, we have developed a practical, efficient and scalable chemical process for the conversion of artemisinic acid to artemisinin using a chemical source of singlet oxygen, thus avoiding the need for specialized photochemical equipment. The strains and processes described here form the basis of a viable industrial process for the production of semi-synthetic artemisinin to stabilize the supply of artemisinin for derivatization into active pharmaceutical ingredients (for example, artesunate) for incorporation into ACTs. Because all intellectual property rights have been provided free of charge, this technology has the potential to increase provision of first-line antimalarial treatments to the developing world at a reduced average annual price.Before the discovery of the enzymes that complete the biosynthetic pathway of artemisinin production (see Supplementary Fig. 1 for a complete overview), several improvements were made to the original amorphadiene-producing strain Y337 (ref. 3). We replaced the MET3 promoter with the copper-regulated CTR3 promoter (Fig. 1a), enabling restriction of ERG9 expression (ERG9 encodes squalene synthase, which catalyses the competing reaction of joining two farnesyl diphosphate moieties to form squalene) by addition of the inexpensive repressor CuSO 4 to the medium rather than the more expensive methionine 4-6 . Strains Y1516 (P CTR3 -ERG9) and Y337 (P MET3 -ERG9) (Supplementary Table 1) both produced similar amounts of amorphadiene ( Supplementary Fig. 2), demonstrating the equivalence of the MET3 and CTR3 promoters for repression of ERG9 expression. We compared the production of amorphadiene from Y337 with the production of artemisinic acid from Y285, a variant of Y337 that also expressed the amorphadiene oxidase CYP71AV1 (a cytochrome P450) and A. annua CPR1 (...

Malaria, caused by Plasmodium sp , results in almost one million deaths and over 200 million new infections annually. The World Health Organization has recommended that artemisinin-based combination therapies be used for treatment of malaria. Artemisinin is a sesquiterpene lactone isolated from the plant Artemisia annua . However, the supply and price of artemisinin fluctuate greatly, and an alternative production method would be valuable to increase availability. We describe progress toward the goal of developing a supply of semisynthetic artemisinin based on production of the artemisinin precursor amorpha-4,11-diene by fermentation from engineered Saccharomyces cerevisiae , and its chemical conversion to dihydroartemisinic acid, which can be subsequently converted to artemisinin. Previous efforts to produce artemisinin precursors used S. cerevisiae S288C overexpressing selected genes of the mevalonate pathway [Ro et al. (2006) Nature 440:940–943]. We have now overexpressed every enzyme of the mevalonate pathway to ERG20 in S. cerevisiae CEN.PK2, and compared production to CEN.PK2 engineered identically to the previously engineered S288C strain. Overexpressing every enzyme of the mevalonate pathway doubled artemisinic acid production, however, amorpha-4,11-diene production was 10-fold higher than artemisinic acid. We therefore focused on amorpha-4,11-diene production. Development of fermentation processes for the reengineered CEN.PK2 amorpha-4,11-diene strain led to production of > 40 g/L product. A chemical process was developed to convert amorpha-4,11-diene to dihydroartemisinic acid, which could subsequently be converted to artemisinin. The strains and procedures described represent a complete process for production of semisynthetic artemisinin.

Mycobacterium tuberculosis, the causative agent of human tuberculosis, is unique among bacterial pathogens in that it displays a wide array of complex lipids and lipoglycans on its cell surface. One of the more remarkable lipids is a sulfated glycolipid, termed sulfolipid-1 (SL-1), which is thought to mediate specific hostpathogen interactions during infection. However, a direct role for SL-1 in M. tuberculosis virulence has not been established. Here we show that MmpL8, a member of a large family of predicted lipid transporters in M. tuberculosis, is required for SL-1 production. The accumulation of an SL-1 precursor, termed SL 1278, in mmpL8 mutant cells indicates that MmpL8 is necessary for an intermediate step in the SL-1 biosynthesis pathway. We use a novel fractionation procedure to demonstrate that SL-1 is present on the cell surface, whereas SL 1278 is found exclusively in more internal layers. Importantly, we show that mmpL8 mutants are attenuated for growth in a mouse model of tuberculosis. However, SL-1 per se is not required for establishing infection as pks2 mutants, which are defective in an earlier step in SL-1 biosynthesis, have no obvious growth defect. Thus, we hypothesize that either MmpL8 transports molecules in addition to SL-1 that mediate host-pathogen interactions or the accumulation of SL 1278 in mmpL8 mutant cells interferes with other pathways required for growth during the early stages of infection.

Mycobacterium tuberculosis synthesizes specific polyketide lipids that interact with the host and are required for virulence. Using a mass spectrometric approach to simultaneously monitor hundreds of lipids, we discovered that the size and abundance of two lipid virulence factors, phthiocerol dimycocerosate (PDIM) and sulfolipid-1 (SL-1), are controlled by the availability of a common precursor, methyl malonyl CoA (MMCoA). Consistent with this view, increased levels of MMCoA led to increased abundance and mass of both PDIM and SL-1. Furthermore, perturbation of MMCoA metabolism attenuated pathogen replication in mice. Importantly, we detected increased PDIM synthesis in bacteria growing within host tissues and in bacteria grown in culture on odd-chain fatty acids. Because M. tuberculosis catabolizes host lipids to grow during infection, we propose that growth of M. tuberculosis on fatty acids in vivo leads to increased flux of MMCoA through lipid biosynthetic pathways, resulting in increased virulence lipid synthesis. Our results suggest that the shift to host lipid catabolism during infection allows for increased virulence lipid anabolism by the bacterium.lipid virulence factor ͉ metabolic flux ͉ pathogenesis ͉ PDIM ͉ sulfolipid-1

pathogenesis ͉ biochemistry ͉ glycolipid ͉ sulfation T he thick Mycobacterium tuberculosis (M. tb) cell wall consists of numerous glycolipids that are distinctive to the mycobacterial genus, including phosphatidylinositol mannosides, trehalose mycolates, and lipoarabinomannans (1). These molecules are essential for many of the characteristics that distinguish mycobacterial pathogenesis, such as the inhibition of phagosomal maturation, drug resistance, and alteration of the host immune response (2-6). A family of cell surface sulfated lipids (dubbed sulfatides) were identified in M. tb extracts and correlated to strain virulence (7-9). The most abundant sulfatide, termed Sulfolipid-1 (SL-1), consists of a trehalose core, four fatty acyl groups, and a sulfate ester (Fig. 1A) (10-13). Despite the discovery of SL-1 nearly 50 years ago, the biological function of the molecule is not known. Conflicting reports suggest a role for SL-1 in superoxide (O 2 Ϫ ) release from human neutrophils or monocytes, alteration of trehalose dimycolate toxicity, and inhibition of trehalose dimycolate-induced macrophage recruitment (14-19). The relevance of these studies to the physiological role of SL-1 in M. tb infection is debatable.Although the role of SL-1 remains elusive, advances in genetics and metabolite analysis have sped the discovery of genes, proteins, and intermediates associated with SL-1 biosynthesis (20). Currently, three proteins are known to be involved in SL-1 assembly: Stf0, Pks2, and MmpL8. The sulfotransferase Stf0 sulfates trehalose at the 2-position, forming trehalose-2-sulfate (T2S), thereby initiating SL-1 biosynthesis (21). Meanwhile, the polyketide synthase Pks2 synthesizes the phthioceranoyl and hydroxyphthioceranoyl lipids that occupy the 6-, 6Ј-, and 3Ј-positions of SL-1 (Fig. 1 A) (22). The proteins responsible for transfer of the Pks2 products and the palmitoyl group to the T2S core, and the order in which these lipids are added, have not yet been defined.Insight into the order of lipid addition came from characterization of the putative lipid transporter MmpL8 (23,24). A mutant strain, ⌬mmpL8, lacks SL-1 but accumulates the diacylated intermediate SL 1278 (named for its observed mass) inside the cell (Fig. 1B). This intermediate possesses two of the four SL-1-associated lipids: a hydroxyphthioceranoyl group at the 3Ј-position and a palmitoyl group at the 2Ј-position (24). SL 1278 was recently found to be an immunostimulant in human tuberculosis patients (25). The glycolipid is presented on the surface of M. tb-infected antigen-presenting cells by CD1b, a member of the MHC class I-like CD1 family. Intriguingly, the ⌬mmpL8 mutant, which lacks SL-1 but accumulates SL 1278 , shows attenuated virulence in mice (23,24). By contrast, a ⌬pks2 mutant, which lacks both SL-1 and SL 1278 , is indistinguishable from WT M. tb in mice and guinea pigs (23,26). These observations suggest that SL 1278 , and possibly other SL-1 intermediates, modulate M. tb pathogenesis.In our effort to define the functions of M. tb sulf...

Mycobacterium tuberculosis, the causative agent of tuberculosis, produces unique sulfated metabolites associated with virulence. One such metabolite from M. tuberculosis lipid extracts, S881, has been shown to negatively regulate the virulence of M. tuberculosis in mouse infection studies, and its cell-surface localization suggests a role in modulating host-pathogen interactions. However, a detailed structural analysis of S881 has remained elusive. Here we use high resolution, high mass accuracy, and tandem mass spectrometry to characterize the structure of S881. Exact mass measurements showed that S881 is highly unsaturated, tandem mass spectrometry indicated a polyisoprene-derived structure, and characterization of synthetic structural analogs confirmed that S881 is a previously-undescribed sulfated derivative of dihydromenaquinone-9, the primary quinol electron carrier in M. tuberculosis. To our knowledge, this is the first example of a sulfated menaquinone produced in any prokaryote. Together with previous studies, these findings suggest that this redox cofactor may play a role in mycobacterial pathogenesis.Tuberculosis (TB) affects approximately one third of the world's population and kills approximately two million people a year (1). In order to be an effective pathogen, Mycobacterium tuberculosis, the causative agent of TB, must not only survive the initial onslaught of the host immune response, but also carefully modulate adaptive immunity to allow for bacterial persistence. Sulfated metabolites have been shown to serve as signaling molecules between both symbiotic and pathogenic bacteria and their hosts (2-4), and the sulfate modification is also key to a number of mammalian extracellular signaling events (5). A number of sulfated metabolites have been isolated from the mycobacterial family (6-9), many of which are found in the cell wall (10,11). While the best-characterized of these molecules is the M. tuberculosis-specific metabolite sulfolipid-1 (SL-1) (9,12), another sulfated metabolite identified in M. tuberculosis lipid extracts has also been localized to the outer envelope of the cell (8,10). This previously-uncharacterized metabolite was termed S881 based on its measured mass. Isotopic labeling of S881 with 34 SO 4 2− indicated that it contains only one sulfate moiety (8,10). Despite the identification of this novel metabolite in M. tuberculosis

The study of the metabolome presents numerous challenges, first among them being the cataloging of its constituents. A step in this direction will be the development of tools to identify metabolites that share common structural features. The importance of sulfated molecules in cell-cell communication motivated us to develop a rapid two-step method for identifying these metabolites in microorganisms, particularly in pathogenic mycobacteria. Sulfurcontaining molecules were initially identified by mass spectral analysis of cell extracts from bacteria labeled metabolically with a stable sulfur isotope ( 34 SO 4 2؊ ). To differentiate sulfated from reduced-sulfur-containing molecules, we employed a mutant lacking the reductive branch of the sulfate assimilation pathway. In these sulfur auxotrophs, heavy sulfate is channeled exclusively into sulfated metabolites. The method was applied to the discovery of several new sulfated molecules in Mycobacterium tuberculosis and Mycobacterium smegmatis. Because a sulfur auxotrophic strain is the only requirement of the approach, many microorganisms can be studied in this manner. Such genetic engineering in combination with stable isotopic labeling can be applied to various metabolic pathways and their products.T he modification of primary and secondary metabolites by the addition or removal of sulfate can have a profound influence on their biological properties (1-5). Typically, sulfated molecules are directed outside the cell, where they serve as modulators of cell-cell interactions. As a notable example pertinent to human health, sulfation of the glycans of endothelial CD34 engenders high-affinity binding with the leukocyte adhesion molecule L-selectin, facilitating an interaction that eventually leads to the recruitment of lymphocytes into peripheral lymph nodes (6). Similarly, sulfation of tyrosyl residues found on the chemokine receptor CCR5 is a modification required for binding of HIV gp120 and therefore efficient viral entry (7).The roles of sulfated compounds in prokaryotes and other microbes are less clear. In one well-characterized case, however, sulfation acts as a modulator of cell-cell communication, similar to its role in eukaryotes. The nitrogen-fixing bacterium Sinorhizobium meliloti utilizes a sulfated glycolipid as a secondary messenger to induce root nodulation in its plant host alfalfa (4,8). Mutants lacking the sulfotransferase that installs this sulfate ester are unable to induce root nodulation in alfalfa but gain the ability to colonize the roots of vetch. That sulfation of a single glycolipid plays such a vital role in nitrogen fixation has far-reaching implications for the agricultural community and presents a possible target for chemical or genetic engineering.Sulfation may also be relevant to the process of bacterial pathogenesis (9). Several mycobacteria, including the human pathogens Mycobacterium tuberculosis and Mycobacterium avium, are known to produce sulfated compounds. One example is Sulfatide-1 (SL-1, Fig. 1A), a sulfated glycolipid from M....

The lipid-rich cell wall of Mycobacterium tuberculosis, the agent of tuberculosis, serves as an effective barrier against many chemotherapeutic agents and toxic host cell effector molecules, and it may contribute to the mechanism of persistence. Mycobacterium tuberculosis strains mutated in a 13-gene operon called mce1, which encodes a putative ABC lipid transporter, induce aberrant granulomatous response in mouse lungs. Because of the postulated role of the mce1 operon in lipid importation, we compared the cell wall lipid composition of wild type and mce1 operon mutant M. tuberculosis H37Rv strains. High resolution mass spectrometric analyses of the mce1 mutant lipid extracts showed unbound mycolic acids to accumulate in the cell wall. Quantitative analysis revealed a 10.7 fold greater amount of free mycolates in the mutant compared to that of the wild type strain. The free mycolates were comprised of alpha, methoxy and keto mycolates in the ratio 1:0.9:0.6, respectively. Since the mce1 operon is regulated in vivo, the free mycolates that accumulate during infection may serve as a barrier for M. tuberculosis against toxic products and contribute to the pathogen's persistence.