Engineering Escherichia coli for constitutive production of monophosphoryl lipid A vaccine adjuvant.

During the COVID-19 pandemic, expedient vaccine production has been slowed by the shortage of safe and effective raw materials, such as adjuvants, essential components to enhance the efficacy of vaccines. Monophosphoryl lipid A (MPLA) is a potent and safe adjuvant used in human vaccines, including the Shingles vaccine, Shingrix. 3-O-desacyl-4'-monophosphoryl lipid A (MPL), a representative MPLA adjuvant commercialized by GSK, was prepared via chemical conversion of precursors isolated from Salmonella typhimurium R595. However, the high price of these materials limits their use in premium vaccines. To combat the scarcity and high cost of safe raw materials for vaccines, we need to develop a feasible MPLA production method that is easily scaled up to meet industrial requirements. In this study, we engineered peptidoglycan and outer membrane biosynthetic pathways in Escherichia coli and developed a Escherichia coli strain, KHSC0055, that constitutively produces EcML (E. coli-produced monophosphoryl lipid A) without additives such as antibiotics or overexpression inducers. EcML production was optimized on an industrial scale via high-density fed-batch fermentation, and obtained 2.7 g of EcML (about 135,000 doses of vaccine) from a 30-L-scale fermentation. Using KHSC0055, we simplified the production process and decreased the production costs of MPLA. Then, we applied EcML purified from KHSC0055 as an adjuvant for a COVID-19 vaccine candidate (EuCorVac-19) currently in clinical trial stage III in the Philippines. By probing the efficacy and safety of EcML in humans, we established KHSC0055 as an efficient cell factory for MPLA adjuvant production.

Split-tracrRNA as an efficient tracrRNA system with an improved potential of scalability.

Due to the relatively long sequence, tracrRNAs are chemically less synthesizable than crRNAs, leading to limited scalability of RNA guides for CRISPR-Cas9 systems. To develop shortened versions of RNA guides with improved cost-effectiveness, we have developed a split-tracrRNA system by nicking the 67-mer tracrRNA (tracrRNA(67)). Cellular gene editing assays and in vitro DNA cleavage assays revealed that the position of the nick is critical for maintaining the activity of tracrRNA(67). TracrRNA(41 + 23), produced by nicking in stem loop 2, showed gene editing efficiency and specificity comparable to those of tracrRNA(67). Removal of the loop of stem loop 2 was further possible without compromising the efficiency and specificity when the stem duplex was stabilized via a high GC content. Binding assays and single-molecule experiments suggested that efficient split-tracrRNAs could be engineered as long as their binding affinity to Cas9 and their reaction kinetics are similar to those of tracrRNA(67).

A Fluorescence-Polarization-Based Lipopolysaccharide-Caspase-4 Interaction Assay for the Development of Inhibitors.

Recognition of intracellular lipopolysaccharide (LPS) by Caspase-4 (Casp-4) is critical for host defense against Gram-negative pathogens. LPS binds to the N-terminal caspase activation and recruitment domain (CARD) of procaspase-4, leading to auto-proteolytic activation followed by pro-inflammatory cytokine release and pyroptotic cell death. Aberrant hyper-activation of Casp-4 leads to amplification of the inflammatory response linked to sepsis. While the active site of a caspase has been targeted with peptide inhibitors, inhibition of LPS-Casp-4 interaction is an emerging strategy for the development of selective inhibitors with a new mode of action for treating infectious diseases and sepsis induced by LPS. In this study, a high-throughput screening (HTS) system based on fluorescence polarization (FP) was devised to identify inhibitors of the LPS and Casp-4 interaction. Using HTS and IC50 determination and subsequently showing inhibited Casp-4 activity, we demonstrated that the LPS-Casp-4 interaction is a druggable target for Casp-4 inhibition and possibly a non-canonical inflammatory pathway.

Loss of splicing factor IK impairs normal skeletal muscle development.

BACKGROUND: IK is a splicing factor that promotes spliceosome activation and contributes to pre-mRNA splicing. Although the molecular mechanism of IK has been previously reported in vitro, the physiological role of IK has not been fully understood in any animal model. Here, we generate an ik knock-out (KO) zebrafish using the CRISPR/Cas9 system to investigate the physiological roles of IK in vivo. RESULTS: The ik KO embryos display severe pleiotropic phenotypes, implying an essential role of IK in embryonic development in vertebrates. RNA-seq analysis reveals downregulation of genes involved in skeletal muscle differentiation in ik KO embryos, and there exist genes having improper pre-mRNA splicing among downregulated genes. The ik KO embryos display impaired neuromuscular junction (NMJ) and fast-twitch muscle development. Depletion of ik reduces myod1 expression and upregulates pax7a, preventing normal fast muscle development in a non-cell-autonomous manner. Moreover, when differentiation is induced in IK-depleted C2C12 myoblasts, myoblasts show a reduced ability to form myotubes. However, inhibition of IK does not influence either muscle cell proliferation or apoptosis in zebrafish and C2C12 cells. CONCLUSION: This study provides that the splicing factor IK contributes to normal skeletal muscle development in vivo and myogenic differentiation in vitro.

Rutin inhibits DRP1-mediated mitochondrial fission and prevents ethanol-induced hepatotoxicity in HepG2 cells and zebrafish.

Excessive alcohol consumption causes the cellular and tissue damage. The toxic metabolites of ethanol are harmful to multiple organ systems, such as the central nervous system, skeletal muscles, and liver, and cause alcohol-induced diseases like cancer, as well as induce hepatotoxicity, and alcoholic myopathy. Alcohol exposure leads to a surge in hepatic alcohol metabolism and oxygen consumption, a decrease in hepatic ATP, and the rapid accumulation of lipid within hepatocytes. Several pathologies are closely linked to defective mitochondrial dynamics triggered by abnormal mitochondrial function and cellular homeostasis, raising the possibility that novel drugs targeting mitochondrial dynamics may have therapeutic potential in restoring cellular homeostasis in ethanol-induced hepatotoxicity. Rutin is a phytochemical polyphenol known to protect cells from cytotoxic chemicals. We investigated the effects of rutin on mitochondrial dynamics induced by ethanol. We found that rutin enhances mitochondrial dynamics by suppressing mitochondrial fission and restoring the balance of the mitochondrial dynamics. Mitochondrial elongation following rutin treatment of ethanol exposed cells was accompanied by reduced DRP1 expression. These data suggest that rutin plays an important role in remodeling of mitochondrial dynamics to alleviate hepatic steatosis and enhance mitochondrial function and cell viability.

The crystal structure of a natural DNA polymerase complexed with mirror DNA.

The intrinsic l-DNA binding properties of a natural DNA polymerase was discovered. The binding affinity of Dpo4 polymerase for l-DNA was comparable to that for d-DNA. The crystal structure of Dpo4/l-DNA complex revealed a dimer formed by the little finger domain that provides a binding site for l-DNA.

Erratum: Multicolor fluorescence imaging using a single RGB-IR CMOS sensor for cancer detection with smURFP-labeled probiotics: publisher's note.

[This corrects the article on p. 2951 in vol. 11, PMID: 32637234.].

Extracellular pyruvate kinase M2 facilitates cell migration by upregulating claudin-1 expression in colon cancer cells.

Extensive studies have been reported the non-canonical functions of pyruvate kinase M2 (PKM2) as a kinase, transcriptional regulator, and even cell-to-cell communicator, emphasizing its importance in various signaling pathways. However, the role of secreted PKM2 in cancer progression and its signaling pathway is yet to be elucidated. In this study, we found that extracellular PKM2 enhanced the migration of low-metastatic, benign colon cancer cells by upregulating claudin-1 expression and internalizing it to the cytoplasm and nucleus. Knock-down of claudin-1 significantly reduced extracellular PKM2-induced cell migration. Inhibition of either protein kinase C (PKC) or epidermal growth factor receptor (EGFR) resulted in a reduction of extracellular PKM2-mediated claudin-1 expression, suggesting EGFR-PKC-claudin-1 as a signaling pathway in the extracellular PKM2-mediated tumorigenesis of colon cancer cells.

Dendritic cell activation by an E. coli-derived monophosphoryl lipid A enhances the efficacy of PD-1 blockade.

Cancer immunotherapy is a powerful approach for cancer treatment, but its clinical effects rely on the tumor's immune conditions. In particular, low response rates to PD-1 blockades are highly correlated with impaired T cell priming. Here, we demonstrate that E. coli-derived monophosphoryl lipid A (EcML) activates dendritic cells in a toll-like receptor-4 (TLR-4)-dependent manner and increases the sensitivity of cancer cells to anti-PD-1 immunotherapy. EcML is a mixture of 4'-monophosphoryl lipids A (MPLAs) produced directly by an engineered Escherichia coli strain; it has a unique congener composition that differentiates it from the well-established MPLA adjuvants, 3-O-desacyl-4'-monophosphoryl lipid A and glucopyranosyl lipid A. Given that active dendritic cells initiate adaptive immune responses, we investigated the anti-tumor activity of an aqueous formulation of EcML. Upon sensing EcML via TLR-4, dendritic cells matured into powerful antigen-presenting cells that could stimulate naïve T cells. EcML reduced tumor growth in the B16F10 mouse model via dendritic cell activation and potentiated PD-1 blockade therapy in the B16F10-OVA melanoma model. These data identify EcML as a promising TLR-4 agonist that can induce anti-tumor immune responses and potentiate PD-1 blockade therapy against tumors.

Metabolic engineering of Escherichia coli to produce a monophosphoryl lipid A adjuvant.

Monophosphoryl lipid A (MPLA) species, including MPL (a trade name of GlaxoSmithKline) and GLA (a trade name of Immune Design, a subsidiary of Merck), are widely used as an adjuvant in vaccines, allergy drugs, and immunotherapy to boost the immune response. Even though MPLA is a derivative of lipopolysaccharide (LPS), a component of the outer membrane of Gram-negative bacteria, bacterial strains producing MPLA have not been found in nature nor engineered. In fact, MPLA generation involves expensive and laborious procedures based on synthetic routes or chemical transformation of precursors isolated from Gram-negative bacteria. Here, we report the engineering of an Escherichia coli strain for in situ production and accumulation of MPLA. Furthermore, we establish a succinct method for purifying MPLA from the engineered E. coli strain. We show that the purified MPLA (named EcML) stimulates the mouse immune system to generate antigen-specific IgG antibodies similarly to commercially available MPLA, but with a dramatically reduced manufacturing time and cost. Our system, employing the first engineered E. coli strain that directly produces the adjuvant EcML, could transform the current standard of industrial MPLA production.

The Lipid A 1-Phosphatase, LpxE, Functionally Connects Multiple Layers of Bacterial Envelope Biogenesis.

Although distinct lipid phosphatases are thought to be required for processing lipid A (component of the outer leaflet of the outer membrane), glycerophospholipid (component of the inner membrane and the inner leaflet of the outer membrane), and undecaprenyl pyrophosphate (C55-PP; precursors of peptidoglycan and O antigens of lipopolysaccharide) in Gram-negative bacteria, we report that the lipid A 1-phosphatases, LpxEs, functionally connect multiple layers of cell envelope biogenesis in Gram-negative bacteria. We found that Aquifex aeolicus LpxE structurally resembles YodM in Bacillus subtilis, a phosphatase for phosphatidylglycerol phosphate (PGP) with a weak in vitro activity on C55-PP, and rescues Escherichia coli deficient in PGP and C55-PP phosphatase activities; deletion of lpxE in Francisella novicida reduces the MIC value of bacitracin, indicating a significant contribution of LpxE to the native bacterial C55-PP phosphatase activity. Suppression of plasmid-borne lpxE in F. novicida deficient in chromosomally encoded C55-PP phosphatase activities results in cell enlargement, loss of O-antigen repeats of lipopolysaccharide, and ultimately cell death. These discoveries implicate LpxE as the first example of a multifunctional regulatory enzyme that orchestrates lipid A modification, O-antigen production, and peptidoglycan biogenesis to remodel multiple layers of the Gram-negative bacterial envelope.IMPORTANCE Dephosphorylation of the lipid A 1-phosphate by LpxE in Gram-negative bacteria plays important roles in antibiotic resistance, bacterial virulence, and modulation of the host immune system. Our results demonstrate that in addition to removing the 1-phosphate from lipid A, LpxEs also dephosphorylate undecaprenyl pyrophosphate, an important metabolite for the synthesis of the essential envelope components, peptidoglycan and O-antigen. Therefore, LpxEs participate in multiple layers of biogenesis of the Gram-negative bacterial envelope and increase antibiotic resistance. This discovery marks an important step toward understanding the regulation and biogenesis of the Gram-negative bacterial envelope.

Chimeric crRNAs with 19 DNA residues in the guide region show the retained DNA cleavage activity of Cas9 with potential to improve the specificity.

We demonstrated that 19 out of 20 RNA residues in the guide region of crRNA can be replaced with DNA residues with high GC-contents. The cellular activity of the chimeric crRNAs to disrupt the target gene was comparable to that of the native crRNA.

Caspase-4 disaggregates lipopolysaccharide micelles via LPS-CARD interaction.

Lipopolysaccharides (LPS) are a major component of the outer membrane of Gram-negative bacteria and are pathogen-associated molecular patterns recognized by the TLR4/MD2 complex that induces an inflammatory response. Recently, the cytosolic receptors caspase-4/-5/-11 that bind LPS inside the cell and trigger inflammasome activation or pyroptosis, have been identified. Despite the important roles of caspase-4 in human immune responses, few studies have investigated its biochemical characteristics and interactions with LPS. Since caspase-4 (C258A) purified from an Escherichia coli host forms aggregates, monomeric proteins including full-length caspase-4, caspase-4 (C258A), and the CARD domain of caspase-4 have been purified from the insect cell system. Here, we report the overexpression and purification of monomeric caspase-4 (C258A) and CARD domain from E. coli and demonstrate that purified caspase-4 (C258A) and CARD domain bind large LPS micelles and disaggregate them to small complexes. As the molar ratio of caspase-4 to LPS increases, the size of the caspase-4/LPS complex decreases. Our results present a new function of caspase-4 and set the stage for structural and biochemical studies, and drug discovery targeting LPS/caspase-4 interactions by establishing a facile purification method to obtain large quantities of purified caspase-4 (C258A) and the CARD domain.

Highly tumor-specific DNA nanostructures discovered by in vivo screening of a nucleic acid cage library and their applications in tumor-targeted drug delivery.

Enormous efforts have been made to harness nanoparticles showing extravasation around tumors for tumor-targeted drug carriers. Owing to the complexity of in vivo environments, however, it is very difficult to rationally design a nanoconstruct showing high tumor specificity. Here, we show an approach to develop tumor-specific drug carriers by screening a library of self-assembled nucleic acid cages in vivo. After preparation of a library of 16 nucleic acid cages by combining the sugar backbone and the shape of cages, we screened the biodistribution of the cages intravenously injected into tumor-bearing mice, to discover the cages with high tumor-specificity. This tumor specificity was found to be closely related with serum stability, cancer cell uptake efficiency, and macrophage evasion rate. We further utilized the cages showing high tumor specificity as carriers for the delivery of not only a cytotoxic small molecule drug but also a macromolecular apoptotic protein exclusively into the tumor tissue to induce tumor-specific damage. The results demonstrate that our library-based strategy to discover tumor-targeted carriers can be an efficient way to develop anti-cancer nanomedicines with tumor specificity and enhanced potency.

Biochemical and Structural Insights into an Fe(II)/α-Ketoglutarate/O2-Dependent Dioxygenase, Kdo 3-Hydroxylase (KdoO).

During lipopolysaccharide biosynthesis in several pathogens, including Burkholderia and Yersinia, 3-deoxy-d-manno-oct-2-ulosonic acid (Kdo) 3-hydroxylase, otherwise referred to as KdoO, converts Kdo to d-glycero-d-talo-oct-2-ulosonic acid (Ko) in an Fe(II)/α-ketoglutarate (α-KG)/O2-dependent manner. This conversion renders the bacterial outer membrane more stable and resistant to stresses such as an acidic environment. KdoO is a membrane-associated, deoxy-sugar hydroxylase that does not show significant sequence identity with any known enzymes, and its structural information has not been previously reported. Here, we report the biochemical and structural characterization of KdoO, Minf_1012 (KdoMI), from Methylacidiphilum infernorum V4. The de novo structure of KdoMI apoprotein indicates that KdoOMI consists of 13 α helices and 11 ß strands, and has the jelly roll fold containing a metal binding motif, HXDX111H. Structures of KdoMI bound to Co(II), KdoMI bound to α-KG and Fe(III), and KdoMI bound to succinate and Fe(III), in addition to mutagenesis analysis, indicate that His146, His260, and Asp148 play critical roles in Fe(II) binding, while Arg127, Arg162, Arg174, and Trp176 stabilize α-KG. It was also observed that His225 is adjacent to the active site and plays an important role in the catalysis of KdoOMI without affecting substrate binding, possibly being involved in oxygen activation. The crystal structure of KdoOMI is the first completed structure of a deoxy-sugar hydroxylase, and the data presented here have provided mechanistic insights into deoxy-sugar hydroxylase, KdoO, and lipopolysaccharide biosynthesis.

Streptavidin-mirror DNA tetrahedron hybrid as a platform for intracellular and tumor delivery of enzymes.

Despite the extremely high substrate specificity and catalytically amplified activity of enzymes, the lack of efficient cellular internalization limits their application as therapeutics. To overcome this limitation and to harness enzymes as practical biologics for targeting intracellular functions, we developed the streptavidin-mirror DNA tetrahedron hybrid as a platform for intracellular delivery of various enzymes. The hybrid consists of streptavidin, which provides a stoichiometrically controlled loading site for the enzyme cargo and an L-DNA (mirror DNA) tetrahedron, which provides the intracellular delivery potential. Due to the cell-penetrating ability of the mirror DNA tetrahedron of this hybrid, enzymes loaded on streptavidin can be efficiently delivered into the cells, intracellularly expressing their activity. In addition, we demonstrate tumor delivery of enzymes in an animal model by utilizing the potential of the hybrid to accumulate in tumors. Strikingly, the hybrid is able to transfer the apoptotic enzyme specifically into tumor cells, leading to strong suppression of tumor growth without causing significant damage to other tissues. These results suggest that the hybrid may allow anti-proliferative enzymes and proteins to be utilized as anticancer drugs.

Poly-sgRNA/siRNA ribonucleoprotein nanoparticles for targeted gene disruption.

Clustered regularly interspaced short palindromic repeats (CRISPR)-associated protein-9 nuclease (Cas9) can be used for the specific disruption of a target gene to permanently suppress the expression of the protein encoded by the target gene. Efficient delivery of the system to an intracellular target site should be achieved to utilize the tremendous potential of the genome-editing tool in biomedical applications such as the knock-out of disease-related genes and the correction of defect genes. Here, we devise polymeric CRISPR/Cas9 system based on poly-ribonucleoprotein (RNP) nanoparticles consisting of polymeric sgRNA, siRNA, and Cas9 endonuclease in order to improve the delivery efficiency. When delivered by cationic lipids, the RNP nanoparticles built with chimeric poly-sgRNA/siRNA sequences generate multiple sgRNA-Cas9 RNP complexes upon the Dicer-mediated digestion of the siRNA parts, leading to more efficient disruption of the target gene in cells and animal models, compared with the monomeric sgRNA-Cas9 RNP complex.

Crystal structure and activity of Francisella novicida UDP-N-acetylglucosamine acyltransferase.

The first step of lipid A biosynthesis in Escherichia coli (E. coli) is catalyzed by LpxA (EcLpxA), an acyltransferase selective for UDP-N-acetylglucosamine (UDP-GlcNAc) and R-3-hydroxymyristoyl-acyl carrier protein (3-OH-C14-ACP), and is an essential step in majority of Gram-negative bacteria. Since the majority of lipid A species isolated from F. novicida contains 3-OH-C16 or 3-OH-C18 at its C3 and C3' positions, FnLpxA was thought to be selective for longer acyl chain (3-OH-C16 and 3-OH-C18) over short acyl chain (3-OH-C14, 3-OH-C12, and 3-OH-C10). Here we demonstrate that Francisella novicida (F. novicida) lpxA functionally complements an E. coli lpxA knockout mutant and efficiently transfers 3-OH-C14 as well as 3-OH-C16 in E. coli. Our results implicate that the acyl chain length of lipid A is determined by several factors including acyl chain selectivity of LpxA and downstream enzymes, as well as the composition of the acyl-ACP pool in vivo. We also report the crystal structure of F. novicida LpxA (FnLpxA) at 2.06 Å. The N-terminal parallel beta-helix (LßH) and C-terminal alpha-helical domain are similar to other reported structures of LpxAs. However, our structure indicates that the supposed ruler residues for hydrocarbon length, 171L in one monomer and 168H in the adjacent monomer in a functional trimer of FnLpxA, are located just 3.8 Å apart that renders not enough space for binding of 3-OH-C12 or longer acyl chains. This implicates that FnLpxA may have an alternative hydrophobic pocket, or the acyl chain may bend while binding to FnLpxA. In addition, the FnLpxA structure suggests a potential inhibitor binding site for development of antibiotics.

A facile method to prepare large quantities of active caspase-3 overexpressed by auto-induction in the C41(DE3) strain.

Since human Caspase-3, a member of the cysteine protease family, plays important roles not only in the apoptosis pathway as an executioner protein, but also in neurological disorders as a critical factor, biomedical researchers have been interested in the development of modulators of caspase-3 activity. Such studies require large quantities of purified active caspase-3. So far, purification of soluble caspase-3 from full-length human caspase-3 in Escherichia coli (E. coli) yields only several mg from a liter of culture media. Therefore, a number of alternative strategies to purify active caspase-3 have been described in the literature, including refolding and protein engineering. In this study, we systematically study the effects of host E. coli strains and growth conditions on purifications of active caspase-3 from full-length human caspase-3. Using a combination of conditions that include use of the C41(DE3) strain, low-temperature expression, and auto-induction that induces caspase-3 expression depending on metabolic state of the individual host cell, we are able to obtain 14-17 mg caspase-3 per liter of culture, an amount that is about 7 times larger than published results. This optimized expression and purification method for caspase-3 can be easily scaled up to facilitate the demand for active enzyme.