Background and overview[1-2]
Polyphosphate is a composite phosphate formed by polymerizing multiple phosphoric acid molecules, such as tripolyphosphate. It is commonly used in the food industry to prevent sausages from discoloring, help fat mixing, speed up the curing of food, and can keep the protein fiber of meat more moist and help improve its structure. Polyphosphate (inorganic polyphosphate, polyP) is a linear polymer composed of several to hundreds of inorganic phosphate monomers polymerized through high-energy phosphate bonds. Due to the presence of polyphosphate in volcanic vents and deep-sea steam vents, polyphosphate may be produced by high-temperature dehydration of phosphate and was widely present in the early Earth. And because polyphosphate can serve as an energy source for organisms, phosphorylating and activating ethanol, sugar, nucleosides and proteins, it is speculated that it played a certain role in the origin of life. Polyphosphates were discovered a century ago when metachromatin was observed, and were subsequently found to be ubiquitous in cells. The identification results of intracellular polyphosphate metabolism enzymes and corresponding genes suggest that cells have their own enzymes to metabolize polyphosphate, ensuring that intracellular polyphosphate is maintained at a relatively stable level. As a multivalent anion, polyphosphate can chelate important metal ions such as Ca, Mg, Mn, Fe, and Co to form complexes with actin-like fibers. In addition, intracellular polyphosphates sense various metabolic and environmental signals. The widespread existence and effects of polyphosphates indicate that they play an important role in biological evolution and physiological functions. But the role of polyphosphates in the origin and survival of species needs to be further determined.
Role in microorganisms[2]
(1) Regulation of gene expression Polyphosphate is involved in the regulation of gene transcription. The enzyme polyphosphate kinase (polyphosphate hosphatekinase, PPK) deletion mutant strain that synthesizes polyphosphate and the enzyme exopolyphosphate hosphatase (PPX) that hydrolyzes polyphosphate overexpressing strain Functional loss in the stationary phase and sensitivity to hydrogen peroxide, heat shock, osmotic stress, ultraviolet light, and mitomycin indicate that polyphosphate is involved in the expression of a large number of genes and in maintaining the corresponding physiological functions of bacteria. For example, polyphosphate regulates the expression of E. coli rpoS and SOS genes, thereby regulating the expression of stationary phase genes and osmoregulation-related genes, as well as DNA damage repair genes. Gene chip analysis of gene expression in the ppk mutation and wild-type exponential phase of Pseudomonas aeruginosa revealed that approximately 450 genes were down-regulated and 250 genes were up-regulated in the ppk1 mutant. Among the 25 genes with the largest expression differences, 24 were related to group effects (Rao et al. 2009). The expression of iron deficiency response systems (such as pvdS, prpL, aprXDEFA, pchGFEDCBA and tonB) (Ochsner et al. 2002) and type 3 secretion system is down-regulated in mutant bacteria and is not completely dependent on population effects. Furthermore, polyphosphates can interact with RNA polymerase in vitro. Therefore, polyphosphates may be transcriptional regulators, particularly “co-regulators” of virulence factors.
The mechanism by which polyphosphate regulates transcription is unclear. The accumulation of polyphosphate may change the stability of the transcript with RNA polymerase or RNA degradation bodies and increase the concentration of RNA. Polyphosphates can also regulate the initiation of transcription by interacting directly with transcription complexes. There is a positively charged lysine-rich region at the amino acid terminus of Helicobacter pylori σ80 that can bind polyphosphate. Similar domains exist in the sigma factors of other human pathogenic bacteria such as Bordetella pertussis and Coxiella burnetii. The way polyphosphate binds to σ to regulate gene expression may be a strategy commonly used by pathogenic bacteria. Polyphosphates may also function as second messengers. E. coli has many regulatory mechanisms to respond to environmental stress and tight response. For example, when amino acids are lacking, the tight response leads to the activation of relA and the production of a large amount of (p)ppGpp, thereby inhibiting the expression of many genes including ribosome biosynthesis genes. activity, activating the expression of more than 50 genes responsible for stress and starvation; when phosphate is lacking, the phosphate regulatory unit (PhoR) senses low phosphate levels and then activates PhoB. The activated PhoB activates more than 30 genes including alkaline phosphatase Expression of gene phoA. The activities of PhoB and (p)ppGpp ultimately lead to the accumulation of polyphosphate, indicating that the functions of PhoB and (p)ppGpp are completed through high concentrations of polyphosphate.
(2) Bacterial ion channels and DNA uptake polyhydroxybutyrate/calcium/polyphosphate located on the bacterial cell membrane (polyphosphate hydroxybutyrate/calcium/polyphosphate, PHB/Ca2+/polyphosphate ) complex gives bacteria the ability to take up DNA and is also a cation-selective channel. The PHB/Ca2+/polyphosphate complex was first isolated from competent cells and has high transducibility and cation selectivity.
(3) Polyphosphate is related to bacterial movement, biofilm formation, colony effect and sporulation. Bacterial movement includes swimming, group movement and rubbing movement. The movement of ppk or ppx mutant bacteria on semi-solid media was affected to varying degrees. Flagella mediate bacterial swimming and group movement, and cilia are responsible for traveling movements. Therefore, ppk mutations may affect the structure or function of flagella or cilia. Electron microscopy showed that the ppk mutant strain had the same flagellum structure as the wild type, so the ppk mutant strainA key mTOR substrate. One substrate is PHAS-I, also known as eukaryotic translation initiation factor 4 (initiation factor 4 Eforeukaryoti cabot ctranslation, eIF4E) binding protein. Dephosphorylated PHAS-I is able to sequester eIF4E. mTOR can phosphorylate PHASI and release eIF4E, which prompts it to participate in the translation of cell growth and proliferation-related proteins (Miron et al. 2001). Another substrate is 40S ribosomal S6 protein kinase (p70S6 kinase), whose activity can be activated by phosphorylation. Activated p70S60 kinase is able to phosphorylate the 40S ribosomal S6 protein, which increases the translation level of mRNAs with oligopyrimidine tracts at the 5′ end. Polyphosphate has been shown to regulate mTOR activity and function. Polyphosphates with chain lengths of 15 to 750 phosphate units are activators of mTOR kinase and contribute to the phosphorylation and autophosphorylation of mTOR kinase. Expression of yeast exopolyphosphatase (scPPX1) in the human breast cancer cell line MCF-7 significantly inhibits the ability of mitogens, insulin, or amino acids to activate mTOR. And the expression of PPX1 can inhibit the proliferation of MCF-7 in serum-free medium. Polyphosphate regulates the activity of mTOR. The reason may be that polyphosphate regulates the effect of cells on stress such as nutrient deficiency through mTOR, similar to its response to stress in prokaryotes.
(3) Polyphosphate regulates mitochondrial metabolism and Ca2+-related cell death. Polyphosphate exists in the mitochondria of higher organisms and can form polyphosphate similar to the mitochondrial permeability transition pore (mPTP). /Ca2+/PHB complex. mPTP, also known as mitochondrial giant channel, is a non-selective highly conductive channel spanning the inner and outer membranes of mitochondria and is composed of a variety of protein complexes. The opening and formation of mPTP on the inner mitochondrial membrane is thought to be caused by Ca2+-induced permeability transition (MPT), which leads to depolarization of the inner membrane and interruption of ATP synthesis, and is involved in apoptosis and necrosis of various cells. . The polyphosphate/Ca2+/PHB complex in vivo may form part of the mPTP complex. By expressing scPPX1 in liver cancer cells, mesonephric cells and undifferentiated mouse myogenic cells, it was found that polyphosphate affects mitochondrial metabolism and intramitochondrial Ca2+ The accumulation of polyphosphate significantly reduced Ca2+-induced mPTP.
(4) Polyphosphate regulates cell calcification. Research results in the beagle alveolar bone regeneration model and the in vitro osteoblast development model MC3T3-E1 cell line indicate that polyphosphate induces normal osteoblast-like cells. of calcification. Polyphosphate induces calcification of osteoblast-like cells through different pathways. First, polyphosphate may serve as a source of phosphate for cellular calcification. Secondly, polyphosphate hydrolase can produce pyrophosphate (PPi), and the balance between polyphosphate, PPi and Pi regulates cell calcification. Third, polyphosphate can promote the binding of fibroblast growth factors (FGFs) to their receptors and regulate cell calcification. Fourth, polyphosphate induces the expression of calcitonin (osteocalcin), osteogenesis-related transcription factor osterix, bone sialoprotein, and tissue non-specific alkaline phosphatase genes. In bioengineering, however, polyphosphates inhibit calcification at the cartilage-bone substitute interface. Reducing the release of polyphosphate during cartilage tissue formation in vitro can promote the formation of a zone of calcified cartilage (ZCC) between the tissue-bone substitute interface. ZCC prevents the generation of high shear forces between the cartilage-subchondral bone interface, allowing integration between the two tissues even under high mechanical loading.
(5) Polyphosphate regulates blood coagulation. Polyphosphate 70-75 exists in the dense particles of human platelets. It is activated by lectins to release polyphosphate. The released polyphosphate accelerates blood coagulation. Polyphosphate acts on three points of the blood coagulation cascade to accelerate blood coagulation: activating the contact pathway to trigger blood coagulation; accelerating the activation rate of coagulation factor V, resulting in a redundant function of the natural anticoagulant protein-tissue factor channel inhibitor It accelerates the polymerization of fibrin into fibrinogen. In addition, polyphosphates delay clot dissolution by enhancing the activity of antifibrinolytic agents. Polyphosphate and its metabolic enzymes play a very important role in bacterial response to various chemical signal environmental stresses, including SOS repair, tight response, dormancy regulation, etc. High concentrations of bacterial polyphosphates may disrupt the blood coagulation system in sepsis patients. However, clinical experiments have shown that tissue factor channel inhibitors cannot treat sepsis, which is consistent with the fact that polyphosphate accelerates the activation of coagulation factor V and does not require tissue factor channel inhibitors.
Preparation[3]
A method for preparing organic polyphosphate: using potassium phosphoenolpyruvate (PEPK) as a monomer, and using persulfate/sulfite at a mild reaction temperature of no more than 80°C. The redox free radical initiating system is used for aqueous solution polymerization to produce homopolymers of PEPK and copolymers of PEPK and acrylic acid or methacrylic acid comonomers (feeding mass ratio is 1:0.5~1:20); after the polymerization reaction is completed , using organic solvents such as absolute ethanol to directly settle, wash and purify, and shear and dry the polymer to obtain the product.
Main reference materials
[1] Nutritional Science Dictionary
[2] Research progress on polyphosphates and their metabolic enzymes
[3] CN200910201213.X Preparation method of organic polyphosphate
