Metabolic engineering of Escherichia coli for the production of an antifouling agent zosteric acid

Zosteric acid (ZA) is a Zostera species-derived, sulfated phenolic acid compound with antifouling activity and has gained much attention due to its nontoxic and biodegradable characteristics. However, the yield of Zostera species available for ZA extraction is limited by natural factors, such as season, latitude, light, and temperature. Here we report the development of metabolically engineered Escherichia coli strains capable of producing ZA from glucose and glycerol. First, intracellular availability of the sulfur donor 3'-phosphoadenosine-5'-phosphosulfate (PAPS) was enhanced by knocking out the cysH gene responsible for PAPS consumption and overexpressing the genes required for PAPS biosynthesis. Co-overexpression of the genes encoding tyrosine ammonia-lyase, sulfotransferase 1A1, ATP sulfurylase, and adenosine 5'-phosphosulfate kinase constructed ZA producing strain with enhanced PAPS supply. Second, the feedback-resistant forms of aroG and tyrA genes (encoding 3-deoxy-d-arabinoheptulosonate 7-phosphate synthase and chorismate mutase, respectively) were overexpressed to relieve the feedback regulation of L-tyrosine biosynthesis. Third, the pykA gene involved in phosphoenolpyruvate-consuming reaction, the regulator gene tyrR, the competing pathway gene pheA, and the ptsHIcrr genes essential for the PEP:carbohydrate phosphotransferase system were deleted. Moreover, all genes involved in the shikimate pathway and the talA, tktA, and tktB genes in the pentose phosphate pathway were examined for ZA production. The PTS-independent glucose uptake system, the expression vector system, and the carbon source were also optimized. As a result, the best-performing strain successfully produced 1.52 g L^-1 ZA and 1.30 g L^-1p-hydroxycinnamic acid from glucose and glycerol in a 700 mL fed-batch bioreactor.

Structural basis for the substrate recognition mechanism of ATP-sulfurylase domain of human PAPS synthase 2

Sulfation is an essential modification on biomolecules in living cells, and 3'-Phosphoadenosine-5'-phosphosulfate (PAPS) is its unique and universal sulfate donor. Human PAPS synthases (PAPSS1 and 2) are the only enzymes that catalyze PAPS production from inorganic sulfate. Unexpectedly, PAPSS1 and PAPSS2 do not functional complement with each other, and abnormal function of PAPSS2 but not PAPSS1 leads to numerous human diseases including bone development diseases, hormone disorder and cancers. Here, we reported the crystal structures of ATP-sulfurylase domain of human PAPSS2 (ATPS2) and ATPS2 in complex with is product 5'-phosphosulfate (APS). We demonstrated that ATPS2 recognizes the substrates by using family conserved residues located on the HXXH and PP motifs, and achieves substrate binding and releasing by employing a non-conserved phenylalanine (Phe550) through a never observed flipping mechanism. Our discovery provides additional information to better understand the biological function of PAPSS2 especially in tumorigenesis, and may facilitate the drug discovery against this enzyme.

Rational design of a highly efficient catalytic system for the production of PAPS from ATP and its application in the synthesis of chondroitin sulfate

The compound 3'-phosphoadenosine-5'-phosphosulfate (PAPS) serves as a sulfate group donor in the production of valuable sulfated compounds. However, elevated costs and low conversion efficiency limit the industrial applicability of PAPS. Here, we designed and constructed an efficient and controllable catalytic system for the conversion of adenosine triphosphate (ATP) (disodium salt) into PAPS without inhibition from by-products. In vitro and in vivo testing in Escherichia coli identified adenosine-5'-phosphosulfate kinase from Penicillium chrysogenum (PcAPSK) as the rate-limiting enzyme. Based on analysis of the catalytic steps and molecular dynamics simulations, a mechanism-guided "ADP expulsion" strategy was developed to generate an improved PcAPSK variant (L7), with a specific activity of 48.94 U·mg^-1 and 73.27-fold higher catalytic efficiency (kcat/Km) that of the wild-type enzyme. The improvement was attained chiefly by reducing the ADP-binding affinity of PcAPSK, as well as by changing the enzyme's flexibility and lid structure to a more open conformation. By introducing PcAPSK L7 in an in vivo catalytic system, 73.59 mM (37.32 g·L^-1 ) PAPS was produced from 150 mM ATP in 18.5 h using a 3-L bioreactor, and achieved titer is the highest reported to date and corresponds to a 98.13% conversion rate. Then, the PAPS catalytic system was combined with the chondroitin 4-sulfotransferase using a one-pot method. Finally, chondroitin sulfate was transformed from chondroitin at a conversion rate of 98.75%. This strategy has great potential for scale biosynthesis of PAPS and chondroitin sulfate.

Updated perspectives on the cytosolic sulfotransferases (SULTs) and SULT-mediated sulfation

The cytosolic sulfotransferases (SULTs) are Phase II detoxifying enzymes that mediate the sulfate conjugation of numerous xenobiotic molecules. While the research on the SULTs has lagged behind the research on Phase I cytochrome P-450 enzymes and other Phase II conjugating enzymes, it has gained more momentum in recent years. This review aims to summarize information obtained in several fronts of the research on the SULTs, including the range of the SULTs in different life forms, concerted actions of the SULTs and other Phase II enzymes, insights into the structure-function relationships of the SULTs, regulation of SULT expression and activity, developmental expression of SULTs, as well as the use of a zebrafish model for studying the developmental pharmacology/toxicology.

The X-ray crystal structure of APR-B, an atypical adenosine 5'-phosphosulfate reductase from Physcomitrella patens

Sulfonucleotide reductases catalyse the first reductive step of sulfate assimilation. Their substrate specificities generally correlate with the requirement for a [Fe4S4] cluster, where adenosine 5'-phosphosulfate (APS) reductases possess a cluster and 3'-phosphoadenosine 5'-phosphosulfate reductases do not. The exception is the APR-B isoform of APS reductase from the moss Physcomitrella patens, which lacks a cluster. The crystal structure of APR-B, the first for a plant sulfonucleotide reductase, is consistent with a preference for APS. Structural conservation with bacterial APS reductase rules out a structural role for the cluster, but supports the contention that it enhances the activity of conventional APS reductases.

Immobilized enzymes to convert N-sulfo, N-acetyl heparosan to a critical intermediate in the production of bioengineered heparin

Heparin is a critically important anticoagulant drug that is prepared from pig intestine. In 2007-2008, there was a crisis in the heparin market when the raw material was adulterated with the toxic polysaccharide, oversulfated chondroitin sulfate, which was associated with 100 deaths in the U.S. alone. As the result of this crisis, our laboratory and others have been actively pursuing alternative sources for this critical drug, including synthetic heparins and bioengineered heparin. In assessing the bioengineering processing costs it has become clear that the use of both enzyme-catalyzed cofactor recycling and enzyme immobilization will be needed for commercialization. In the current study, we examine the use of immobilization of C₅-epimerase and 2-O-sulfotransferase involved in the first enzymatic step in the bioengineered heparin process, as well as arylsulfotransferase-IV involved in cofactor recycling in all three enzymatic steps. We report the successful immobilization of all three enzymes and their use in converting N-sulfo, N-acetyl heparosan into N-sulfo, N-acetyl 2-O-sulfo heparin.

The structural biology of oestrogen metabolism

Many enzymes catalyse reactions that have an oestrogen as a substrate and/or a product. The reactions catalysed include aromatisation, oxidation, reduction, sulfonation, desulfonation, hydroxylation and methoxylation. The enzymes that catalyse these reactions must all recognise and bind oestrogen but, despite this, they have diverse structures. This review looks at each of these enzymes in turn, describing the structure and discussing the mechanism of the catalysed reaction. Since oestrogen has a role in many disease states inhibition of the enzymes of oestrogen metabolism may have an impact on the state or progression of the disease and inhibitors of these enzymes are briefly discussed. This article is part of a Special Issue entitled 'CSR 2013'.