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Biomedical subjects

Zhihong Guo

Publications and source records attributed to Zhihong Guo.

At least 19 recordsLinked to original sources

High-level terpene production via a novel Actinomycetota-derived MVA pathway in E. coli.

The heterologous production of terpene in microbial hosts is often limited by inefficient and unstable pathway expression, creating a major bottleneck for industrial-scale synthesis. While E. coli as a chassis offers significant advantages, such as rapid growth, ease of cultivation, and genetic tractability. Its endogenous supply of terpenoid precursors remains a critical constraint, fundamentally restricting high-yield production. To address this challenge, we developed a genomically integrated Mevalonate (MVA) pathway from Actinomycetota in E. coli BL21(DE3) to enhance terpene precursor supply. Our approach began with an in silico multi-layer global genome mining analysis of 25,261 Actinomycetota genomes to identify a series of MVA pathway enzymes with potentially high catalytic efficiency, created a high-efficiency chassis E. coli MVA platform (ecMVA-1 and ecMVA-2) for terpene precursor synthesis. Its functionality was validated by testing eight distinct TSs. Among them, the fermentation of artemisinin precursor amorphadiene using a 5-liter bioreactor yielded 947.80 mg/L. These results indicated that E. coli (MVA) is well-suited for TS studies in the laboratory as well as holding significant promise for industrial applications. In addition, this in silico approach offers a new perspective for metabolic engineering and provides potential reservoir of diverse chassis for the industrial production of terpenoid-derived compounds.

Actinomycetota↗

Amino terminus of the SARS coronavirus protein 3a elicits strong, potentially protective humoral responses in infected patients.

The 3a protein of severe acute respiratory syndrome (SARS)-associated coronavirus is expressed and transported to the plasma membrane in tissue cells of infected patients. Its short N-terminal ectodomain was found to elicit strong humoral responses in half of the patients who had recovered from SARS. The ectodomain-specific antibodies from the convalescent-phase plasma readily recognized and induced destruction of 3a-expressing cells in the presence of the human complement system, demonstrating their potential ability to provide immune protection by recognizing and eliminating SARS coronavirus-infected cells that express the target protein. In addition, when coupled to a carrier protein, the ectodomain peptide elicited 3a-specific antibodies in mice and rabbit at high titres. These results showed that the N terminus of the 3a protein is highly immunogenic and elicits potentially protective humoral responses in infected patients. Therefore, the short extracellular domain may be a valuable immunogen in the development of a vaccine for infectious SARS.

Animals↗

Impaired long-term depression in P2X3 deficient mice is not associated with a spatial learning deficit.

The hippocampus is a brain region critical for learning and memory processes believed to result from long-lasting changes in the function and structure of synapses. Recent findings suggest that ATP functions as a neurotransmitter or neuromodulator in the mammalian brain, where it activates several different types of ionotropic and G protein-coupled ATP receptors that transduce calcium signals. However, the roles of specific ATP receptors in synaptic plasticity have not been established. Here we show that mice lacking the P2X3 ATP receptor (P2X3KO mice) exhibit abnormalities in hippocampal synaptic plasticity that can be restored by pharmacological modification of calcium-sensitive kinase and phosphatase activities. Calcium imaging studies revealed an attenuated calcium response to ATP in hippocampal neurons from P2X3KO mice. Basal synaptic transmission, paired-pulse facilitation and long-term potentiation are normal at synapses in hippocampal slices from P2X3KO. However, long-term depression is severely impaired at CA1, CA3 and dentate gyrus synapses. Long-term depression can be partially rescued in slices treated with a protein phosphatase 1-2 A activator or by postsynaptic inhibition of calcium/calmodulin-dependent protein kinase II. Despite the deficit in hippocampal long-term depression, P2X3KO mice performed normally in water maze tests of spatial learning, suggesting that long-term depression is not critical for this type of hippocampus-dependent learning and memory.

Adenosine Triphosphate↗

Wall shear stresses in small and large two-way bypass grafts.

Wall shear stress, as one of the most important hemodynamic parameters of the cardiovascular system, has been studied extensively in the numerical and experimental approaches to blood flow in various arteries. In order to clarify the influence of graft diameter on the wall shear stress in a femoral two-way bypass graft, the pulsatile blood flows in two models were simulated with the finite element method. Both models were constructed with different diameters of grafts. The main geometric structure and the boundary conditions were identical for both models. The emphasis was on the comparison analysis of wall shear stresses in the vicinity of the distal anastomosis. The temporal-spatial distributions of wall shear stresses, wall shear stress gradients, and oscillating shear index were analyzed and compared. The present study indicated that femoral artery bypassed with a large graft demonstrated relatively uniform wall shear stresses and small wall shear stress gradients, whereas it does not have advantages in the oscillating shear index. The large model exhibits better and more regular hemodynamic phenomena and may be effective in decreasing the probability of the initiation and development of postoperative intimal hyperplasia and restenosis. Thus, appropriately large grafts are applicable in the clinical practice of femoral two-way bypass operation. More detailed studies are necessary on this problem for the purpose of increasing the success rates of the femoral bypass grafts.

Anastomosis, Surgical↗

Macrolactonization catalyzed by the terminal thioesterase domain of the nonribosomal peptide synthetase responsible for lichenysin biosynthesis.

The excised terminal thioesterase of the lichenysin nonribosomal peptide synthetase was found to be a highly efficient and versatile enzyme. Its activity strictly requires the R configuration of the beta-hydroxy fatty acid and the side chains of aspartate-5 and isoleucine-7, but tolerates changes in five other residues of the substrate. Characterization of this enzyme facilitates future effort to engineer the lichenysin synthetase for biotechnological applications.

Catalysis↗

Self-propagating, molecular-level polymorphism in Alzheimer's beta-amyloid fibrils.

Amyloid fibrils commonly exhibit multiple distinct morphologies in electron microscope and atomic force microscope images, often within a single image field. By using electron microscopy and solid-state nuclear magnetic resonance measurements on fibrils formed by the 40-residue beta-amyloid peptide of Alzheimer's disease (Abeta(1-40)), we show that different fibril morphologies have different underlying molecular structures, that the predominant structure can be controlled by subtle variations in fibril growth conditions, and that both morphology and molecular structure are self-propagating when fibrils grow from preformed seeds. Different Abeta(1-40) fibril morphologies also have significantly different toxicities in neuronal cell cultures. These results have implications for the mechanism of amyloid formation, the phenomenon of strains in prion diseases, the role of amyloid fibrils in amyloid diseases, and the development of amyloid-based nano-materials.

Amino Acid Motifs↗

B-cell responses in patients who have recovered from severe acute respiratory syndrome target a dominant site in the S2 domain of the surface spike glycoprotein.

Severe acute respiratory syndrome (SARS) is a recently emerged infectious disease caused by a novel strain of coronavirus. Examination of the immune responses of patients who have recovered from SARS should provide important information for design of a safe and effective vaccine. We determined the continuous viral epitopes targeted by antibodies in plasma samples from convalescent SARS patients through biopanning with a vast M13 phage display dodecapeptide library. These epitopes converged to very short peptide fragments, one on each of the structural proteins spike and nucleocapsid and the nonstructural proteins 3a, 9b, and nsp 3. Immunoassays found that most of the patients who had recovered from SARS developed complementary antibodies to the epitope-rich region on the spike S2 protein, indicating that this is an immunodominant site on the viral envelope comprising the spike, matrix, and small envelope glycoproteins. These S2-targeting antibodies were shown to effectively neutralize the coronavirus, indicating that they provided protective immunity to help the patients recover from the viral infection. These results suggest that the SARS coronavirus might have an antigenic profile distinct from those of other human or animal coronaviruses. Due to the tested safety and protective effects of the convalescent-phase serological antibodies, identification of their complementary antigens may enable the design of an epitope-based vaccine to prevent potential antibody-mediated immunopathology.

Adult↗

Dopamine as a robust anchor to immobilize functional molecules on the iron oxide shell of magnetic nanoparticles.

We report on the use of dopamine (DA) as a robust molecular anchor to link functional molecules to the iron oxide shell of magnetic nanoparticles. Using nitrilotriacetic acid (NTA) as the functional molecule, we created a system with an M/Fe2O3-DA-NTA (M = Co or SmCo5.2) nanostructure, which possesses high stability and specificity for separating histidine-tagged proteins. The well-established biocompatibility of iron oxide and the robust covalent bonds between DA and Fe2O3 render this strategy attractive for constructing biofunctional magnetic nanoparticles containing iron oxide.

Dopamine↗

Synthesis of gramicidin S and its analogues via an on-resin macrolactamization assisted by a predisposed conformation of the linear precursors.

A simple and efficient preparation of gramicidin S and its analogues is described. It involves solid-phase peptide synthesis and on-resin macrolactamization without side chain protection, affording cyclic products in high yield and high purity. The high specificity of the cyclization reaction was shown to originate in the formation of a pre-organized conformation of the linear biosynthetic precursor of gramicidin S. This facile method will provide convenient access to the analogues of the natural product for functional optimization to counter microbial resistance.

Alanine↗

Nitrilotriacetic acid-modified magnetic nanoparticles as a general agent to bind histidine-tagged proteins.

Using Nalpha,Nalpha-bis(carboxymethyl)lysine to react with FePt magnetic nanoparticles, we synthesized the FePt-NTA conjugate, which immobilizes Ni2+ ions and selectively binds to histidine-tagged proteins at concentration as low as 0.5 pM. This simple system serves as a useful alternative to existing protocols for protein separation and also acts as a versatile agent for transporting and anchoring proteins.

Alloys↗

Paroxetine retards disease onset and progression in Huntingtin mutant mice.

We report that administration of paroxetine, a widely prescribed antidepressant drug that acts by inhibiting reuptake of the neurotransmitter serotonin, suppresses the neurodegenerative process and increases the survival of huntingtin mutant mice, an animal model of Huntington's disease (HD). Paroxetine attenuated motor dysfunction and body weight loss and improved glucose metabolism in the HD mice. Paroxetine was beneficial when treatment was initiated before or after the onset of motor dysfunction, suggesting a potential for such antidepressant drugs in the treatment of presymptomatic and symptomatic HD patients.

Animals↗

Bone marrow transplantation reveals roles for brain macrophage/microglia TNF signaling and nitric oxide production in excitotoxic neuronal death.

The signaling mechanisms by which brain macrophages and microglia (BMM) respond to injury and disease, and how their responses affect neurodegenerative processes are largely unknown. Here we show that bone marrow transplantation can be used to introduce genetically modified BMM into the adult mouse brain to reveal the functions of one or more BMM genes in neuronal injury responses. Mice in which endogenous BMM were replaced with cells from mice lacking p55 and p75 tumor necrosis factor (TNF) receptors exhibit increased vulnerability of hippocampal neurons to excitotoxic injury suggesting a role for TNF signaling in BMM in the excitotoxic injury response. Neurons in the brains of mice with BMM lacking nitric oxide synthase exhibit reduced protein nitration and are less vulnerable to excitotoxic damage, indicating a pivotal role for BMM nitric oxide production in excitotoxic neuronal damage.

Animals↗

Prophylactic activation of neuroprotective stress response pathways by dietary and behavioral manipulations.

It is well established that when most types of cells, including neurons, are exposed to a mild stress they increase their ability to resist more severe stress. This "preconditioning" phenomenon involves up-regulation of genes that encode cytoprotective proteins such as heat-shock proteins and growth factors. We found that a similar beneficial cellular stress response can be induced in neurons throughout the brain by a "meal-skipping" dietary restriction (DR) regimen in rats and mice. DR is effective in protecting neurons and improving functional outcome in models of stroke, Alzheimer's, Parkinson's and Huntington's diseases. DR induces an increase in the levels of brain-derived neurotrophic factor (BDNF) and heat-shock proteins in neurons. DR also stimulates neurogenesis in the hippocampus, and BDNF plays a role in this effect of DR. Physical exercise and environmental enrichment are two other manipulations that have been shown to induce BDNF expression in the brain, presumably because it is a mild cellular stress. When taken together with epidemiological and clinical studies in humans, the data from animal studies suggest that it may be possible to reduce the risk for age-related neurodegenerative disorders through dietary and behavioral modifications that act by promoting neuronal plasticity and survival.

Alzheimer Disease↗

Dissociation of antibacterial and hemolytic activities of an amphipathic peptide antibiotic.

Using an alanine-scanning method, we have found that the antibacterial and hemolytic activities of the amphipathic cyclic decapeptide antibiotic tyrocidine A depend on different structural components. Single substitution of glutamine-6 of the natural product with a cationic amino acid results in a therapeutic index enhancement of up to 140-fold. Successful dissociation of the two intimately associated properties should enable discovery of novel analogues with both high bacterial selectivity and antibacterial potency to counter microbial resistance.

Amino Acid Substitution↗

Biomimetic synthesis of gramicidin s and analogues by enzymatic cyclization of linear precursors on solid support.

[reaction: see text] Gramicidin S is a potent decapeptide antibiotic with high hemolytic activity but is unlikely to provoke microbial resistance. Here we demonstrate that gramicidin thioesterase (GrsB TE) correctly cyclizes immobilized linear decapeptide precursors into head-to-tail products, indicating its suitability for parallel solid-phase synthesis of gramicidin analogues from linear precursors on solid support. This chemoenzymatic method will enable the optimization of the therapeutic index of the natural product to fight microbial resistance.

Anti-Bacterial Agents↗

The biosynthesis of GDP-L-colitose: C-3 deoxygenation is catalyzed by a unique coenzyme B6-dependent enzyme.

l-Colitose (1) is a 3,6-dideoxyhexose found in the O-antigen of gram-negative lipopoly-saccharides. While the biosynthesis of many deoxysugars have previously been investigated, l-colitose is distinct in that it originates from GDP-d-mannose. In contrast, other 3,6-dideoxyhexoses arise from CDP-d-glucose. Therefore, the enzymes involved in the l-colitose biosynthetic pathway must be specifically tailored to utilize such a modified substrate. The mode for deoxygenation at C-3 of colitose is of particular interest because this conversion in other naturally occurring 3,6-dideoxyhexoses requires a pair of enzymes, E1 and E3, acting in concert. Interestingly, no E3 equivalent was identified in the five open reading frames of the col biosynthetic gene cluster from Yersinia pseudotuberculosis IVA. However, the gene product of colD showed moderate similarity with the E1 gene (ddhC/ascC) of the ascarylose pathway (27% identity and 42% similarity). Because E1 is a pyridoxamine 5'-phosphate (PMP)-dependent enzyme, it was thought that ColD might also utilize PMP. Indeed, turnover was observed during incubation of ColD with substrate in the presence of excess PMP, but not with pyridoxal 5'-phosphate (PLP). However, the rate of product formation increased by more than 40-fold when l-glutamate was included in the PLP incubation. The formation of alpha-ketoglutarate as a byproduct under these conditions clearly indicated that ColD functions as a transaminase, recognizing both PMP and PLP. In this paper, we propose a novel biosynthetic route for colitose, including the unprecedented C-3 deoxygenation performed solely by ColD. The utilization of PMP in a dehydration reaction is rare, but the combined deoxygenation-transamination activity makes ColD a unique enzyme.

Guanosine Diphosphate Sugars↗