Beetin

Last updated

Beetin (BE27 or BE29) is a ribosome-inactivating protein found in the leaves of sugar beets, Beta vulgaris L, specifically attacking plant ribosomes. [1] Sugar beet, beetins, that have been isolated meet all the criteria to be classified as single chain (type 1) ribosome inactivating proteins that are highly toxic to mammalian ribosomes but non-toxic to intact cultured mammalian cells. [1] Beetin expression occurs when there is a viral infection of the plant. [2] The different levels of glycosylation of the same polypeptide chain result in the two forms of beetin (BE27 or BE29). [3] Beetin exhibits these two primary forms with apparent Mr values of 27 000 (BE27) and 29 000 (BE29) along with  possessing glycan chains. [1] Beetins are a type-I (single-chain) proteins with N-glycoside activity. Since it has been discovered that beetin is mostly concentrated in the intercellular fluid, its presence in the remaining parts of the leaf may be below the limit of detection rather than being nonexistent. [1] The expression of beetin is only found in mature plants, but is present in all developing stages. [2] [1]

Contents

Structure

The beetin RIP exhibits the typical fold of type 1 RIPs and the A chain of type 2 RIPs, in which the intersection of three domains results in the active site. These domains are the N-terminal domain 1, which has β-strands and α-helices; domain 2, which has α-helices; and the C-terminal domain 3, which has two α-helices and two β-strands. BE27 displays a conformation of the loop lining the catalytic site cleft (from amino acids 84 to 122) but does not show a negatively charged patch near to the active site cleft. [3]

Role as antiviral protein

Beet 27 is also an antiviral protein that acts as a defense mechanism to protect the plant from a viral infection. This action can be induced by compounds like salicylic acid and hydrogen peroxide. Beet 27 does have the special ability of superoxide dismutase activity, being able to produce the compound, hydrogen peroxide.The hydrogen peroxide produced is toxic to attackers or it is also able to either directly or indirectly stimulate plant defense responses. The defensive ability has been directly linked to adenosine glycosidase activity from the RNA polynucleotide. [3] Beetin levels are regulated post-transcriptionally during the growth of the plant Beta Vulgaris. [2] Beetin's function as a defense protein has been related to its RNA polynucleotide: adenosine glycosidase activity on viral RNA since it depurinates the tobacco mosaic virus RNA whereas beet ribosomes are not sensitive to BE27. Beetin's topical antiviral action is compatible with the antiviral function now suggested for RIPs. [3] The idea that beetin could cause the inactivation of the damaged cells' ribosomes and so prevent viral replication cannot be completely ruled out because the local lesion assay necessitates the abrasion of the leaf surface with carborundum. [1] These biological abilities are of interest because they could potentially lead to a broad action treatment of several known pathogens. Studies are currently being done in vitro to understand the extent of this defense mechanism and the range of treatment types for infections from viruses, bacteria, fungi, and even insects. [3]

Role as antifungal protein

It is thought that Type 1 RIPs (found in the apoplasm) may be a component of certain higher plants' general suicide strategy since they render injured tissue ineffective for the establishment of a viral or parasitic fungal infection. [3] Beetin has been found as a defense protein reacting to viral infections, but it has also been tested to see if beetin have antifungal properties. [4] On both bacterial and fungal ribosomes, BE27 exhibits rRNA N-glycosidase activity. [3] The carboxy-terminal amino acid sequence of defensins, which is distinguished by the presence of two antiparallel -strands with an interposed loop and is preceded by a -helix, has been reported to be a primary determinant of the antifungal activity of defensins. BE27 was able to enter the cytosol and kill fungal cells at quantities lower than those observed in the apoplast, halting the growth of the fungus. The activity of rRNA N-glycosylase on the SRL of the large-subunit rRNA, which irreversibly deactivates the fungal ribosomes and prevents protein synthesis, appeared to be the mechanism of action. Researchers discovered that when a smear of damaged DNA was seen in fungus that had been exposed to BE27 compared to the untreated control, no internucleosomal cleavage was apparent, indicating that BE27 intoxication can happen through non-apoptotic pathways. Cultures have shown that they did not exhibit internucleosomal cleavage after exposure to BE27, indicating that ribosome inactivation followed by necrotic cell death is the mechanism by which fungal growth is inhibited. [4]

Research findings

Beetin production has two different mechanisms of regulation including the control of translation and the control of transcription which coexist. [2] When Beetin was sequenced it was found that this type of ribosome inactivating protein has a single peptide. In a study done with analyzing N-terminal amino acid sequences, both BE27 and BE29 have shown to be closely related due to both proteins having the sequence H2N-ADVTFDLETASKTKYGTFLSNLRNI… BE29 is more glycosylated than BE27, as BE27 is a non-glycosylated form of Beetin. [1]

Beetin 27 (BE27) has anti-pathogenic properties that are activated when exposed to hydrogen peroxide and salicylic acid. [3] Beetin RIPs are 28S ribosomal RNA N-glycosylases that cleave a bond between adenine 4324 and its ribosome in the 60S subunit of ribosome. This adenine is located in the Sarcin Ricin Loop which is most important for anchoring the EFG or EF-2 elongation factors on the ribosome during mRNA transfer. [4] BE27 activity shows that as a rRNA N-glycosidase splits an adenine from the Sarcin Ricin Loop from the mammalian 28S rRNA which disables the ribosomes from binding the Elongation Factor 2 and arresting protein synthesis. Along with rRNA glycosidase activity, there was some endonuclease activity based on the relationship between BE27 and the plasmid PUC19. It was found that BE27 promoted the change of supercoiled PUC19 DNA to a more relaxed, linear form. [3] In the three arbitrary stages of growth, beetin RNA transcripts of beetin were shown to be constitutively produced at high quantities by Northern blot studies, but they were not translated in germ plants or 2-week-old plants. Additionally, it was discovered that the H2O2-induced induction of beetin seemed to occur only in plantlets that were 4 weeks old, showing that the elicitor-dependent production of beetin is developmentally controlled. As more mediators like salicylic acid or hydrogen peroxide are added as treatment to the sugar beet plants the more expression of beetin is shown. [2] Beetin may only be present in mature plants, but it was found that the induction of the beetin with H2O2 or artichoke mottled crinkle virus (AMCV) has shown beetin expression in both new and old leaves with around the same intensity of expression. [1] Expression studies have shown that beetin is highly effective against E. coli ribosomes because they become depurinated as the bacteria develops and beetin in created and accumulates inside the cells. [3]

See also

Related Research Articles

<span class="mw-page-title-main">Interferon</span> Signaling proteins released by host cells in response to the presence of pathogens

Interferons are a group of signaling proteins made and released by host cells in response to the presence of several viruses. In a typical scenario, a virus-infected cell will release interferons causing nearby cells to heighten their anti-viral defenses.

<span class="mw-page-title-main">Protein biosynthesis</span> Assembly of proteins inside biological cells

Protein biosynthesis is a core biological process, occurring inside cells, balancing the loss of cellular proteins through the production of new proteins. Proteins perform a number of critical functions as enzymes, structural proteins or hormones. Protein synthesis is a very similar process for both prokaryotes and eukaryotes but there are some distinct differences.

<span class="mw-page-title-main">Antiviral drug</span> Medication used to treat a viral infection

Antiviral drugs are a class of medication used for treating viral infections. Most antivirals target specific viruses, while a broad-spectrum antiviral is effective against a wide range of viruses. Antiviral drugs are one class of antimicrobials, a larger group which also includes antibiotic, antifungal and antiparasitic drugs, or antiviral drugs based on monoclonal antibodies. Most antivirals are considered relatively harmless to the host, and therefore can be used to treat infections. They should be distinguished from virucides, which are not medication but deactivate or destroy virus particles, either inside or outside the body. Natural virucides are produced by some plants such as eucalyptus and Australian tea trees.

<span class="mw-page-title-main">Sugar beet</span> Plant grown commercially for sugar production

A sugar beet is a plant whose root contains a high concentration of sucrose and which is grown commercially for sugar production. In plant breeding, it is known as the Altissima cultivar group of the common beet. Together with other beet cultivars, such as beetroot and chard, it belongs to the subspecies Beta vulgaris subsp. vulgaris. Its closest wild relative is the sea beet.

<span class="mw-page-title-main">Ricin</span> Type of toxic lectin

Ricin ( RY-sin) is a lectin (a carbohydrate-binding protein) and a highly potent toxin produced in the seeds of the castor oil plant, Ricinus communis. The median lethal dose (LD50) of ricin for mice is around 22 micrograms per kilogram of body weight via intraperitoneal injection. Oral exposure to ricin is far less toxic. An estimated lethal oral dose in humans is approximately 1 milligram per kilogram of body weight.

<i>Beta vulgaris</i> Species of flowering plant

Beta vulgaris (beet) is a species of flowering plant in the subfamily Betoideae of the family Amaranthaceae. Economically, it is the most important crop of the large order Caryophyllales. It has several cultivar groups: the sugar beet, of greatest importance to produce table sugar; the root vegetable known as the beetroot or garden beet; the leaf vegetable known as chard or spinach beet or silverbeet; and mangelwurzel, which is a fodder crop. Three subspecies are typically recognised. All cultivars, despite their quite different morphologies, fall into the subspecies Beta vulgaris subsp. vulgaris. The wild ancestor of the cultivated beets is the sea beet.

Ribosome shunting is a mechanism of translation initiation in which ribosomes bypass, or "shunt over", parts of the 5' untranslated region to reach the start codon. However, a benefit of ribosomal shunting is that it can translate backwards allowing more information to be stored than usual in an mRNA molecule. Some viral RNAs have been shown to use ribosome shunting as a more efficient form of translation during certain stages of viral life cycle or when translation initiation factors are scarce. Some viruses known to use this mechanism include adenovirus, Sendai virus, human papillomavirus, duck hepatitis B pararetrovirus, rice tungro bacilliform viruses, and cauliflower mosaic virus. In these viruses the ribosome is directly translocated from the upstream initiation complex to the start codon (AUG) without the need to unwind RNA secondary structures.

Cyanovirin-N (CV-N) is a protein produced by the cyanobacterium Nostoc ellipsosporum that displays virucidal activity against several viruses, including human immunodeficiency virus (HIV). A cyanobacterial protein called cyanovirin-N (CV-N) has strong anti-human immunodeficiency virus (HIV) neutralizing properties. The virucidal activity of CV-N is mediated through specific high-affinity interactions with the viral surface envelope glycoproteins gp120 and gp41, as well as to high-mannose oligosaccharides found on the HIV envelope. In addition, CV-N is active against rhinoviruses, human parainfluenza virus, respiratory syncytial virus, and enteric viruses. The virucidal activity of CV-N against influenza virus is directed towards viral haemagglutinin.

<span class="mw-page-title-main">Gelonin</span>

Gelonin is a type 1 ribosome-inactivating protein and toxin of approximately 30 kDa found in the seeds of the Himalayan plant Gelonium multiflorum. In cell-free systems gelonin exerts powerful N-glycosidase activity on the 28S rRNA unit of eukaryotic ribosomes by cleaving out adenine at the 4324 site. Gelonin lacks carbohydrate-binding domains so it is unable to cross the plasma membrane, making it highly effective only in cell free systems.

<span class="mw-page-title-main">Hepatitis A virus internal ribosome entry site (IRES)</span>

This family represents the internal ribosome entry site (IRES) of the hepatitis A virus. HAV IRES is a 450 nucleotide long sequence located in the 735 nt long 5’ UTR of Hepatitis A viral RNA genome. IRES elements allow cap and end-independent translation of mRNA in the host cell. The IRES achieves this by mediating the internal initiation of translation by recruiting a ribosomal 40S pre-initiation complex directly to the initiation codon and eliminates the requirement for eukaryotic initiation factor, eIF4F.

Saporin is a protein that is useful in biological research applications, especially studies of behavior. Saporins are so-called ribosome inactivating proteins (RIPs), due to its N-glycosidase activity, from the seeds of Saponaria officinalis. It was first described by Fiorenzo Stirpe and his colleagues in 1983 in an article that illustrated the unusual stability of the protein.

<span class="mw-page-title-main">Ribosome-inactivating protein</span> Protein synthesis inhibitor

A ribosome-inactivating protein (RIP) is a protein synthesis inhibitor that acts at the eukaryotic ribosome. This protein family describes a large family of such proteins that work by acting as rRNA N-glycosylase. They inactivate 60S ribosomal subunits by an N-glycosidic cleavage, which releases a specific adenine base from the sugar-phosphate backbone of 28S rRNA. RIPs exist in bacteria and plants.

<span class="mw-page-title-main">Antiviral protein</span>

Antiviral proteins are proteins that are induced by human or animal cells to interfere with viral replication. These proteins are isolated to inhibit the virus from replicating in a host's cells and stop it from spreading to other cells. The Pokeweed antiviral protein and the Zinc-Finger antiviral protein are two major antiviral proteins that have undergone several tests for viruses, including HIV and influenza.

<span class="mw-page-title-main">Betaenone C</span> Chemical compound

Betaenone C, like other betaenones, is a secondary metabolite isolated from the fungus Pleospora betae, a plant pathogen. Of the seven phytotoxins isolated in fungal leaf spots from sugar beet, it showed 89% growth inhibition. Betaenone C has been shown to act by inhibiting RNA and protein synthesis.

rRNA endonuclease is an enzyme that catalyses the hydrolysis of the phosphodiester linkage between guanosine and adenosine residues at one specific position in the 28S rRNA of rat ribosomes. This enzyme also acts on bacterial rRNA.

<span class="mw-page-title-main">RRNA N-glycosylase</span>

rRNA N-glycosylase is an enzyme with systematic name rRNA N-glycohydrolase. This enzyme catalyses the following chemical reaction

Cucurmosin is a type I ribosome inactivating protein (RIP) found in the sarcocarp (flesh) and seed of Cucurbita — notably Cucurbita moschata, that is toxic to cancer cells, if the dosage is high enough, by stopping their ribosomes. Cucurmosin is what Cucurbita use to defend against viral, fungal, and bacterial agents. It takes a lower dose of cucurmosin to kill cancer cells than healthy cells. It has been shown to induce apoptosis in pancreatic cancer and myeloid leukemia cells.

Oncomatryx Biopharma S. L. is a pharmaceutical biotechnology company that develops personalized treatments against invasive cancer as well as tests for its early detection. Established by Laureano Simón, PhD, Oncomatryx thus engages twofold in the fight against invasive kinds of cancer, such as pancreatic cancer or invasive breast cancer, all of which have high mortality rates.

An interferon-stimulated gene (ISG) is a gene that can be expressed in response to stimulation by interferon. Interferons bind to receptors on the surface of a cell, initiating protein signaling pathways within the cell. This interaction leads to the expression of a subset of genes involved in the innate immune system response. ISGs are commonly expressed in response to viral infection, but also during bacterial infection and in the presence of parasites.It's currently estimated that 10% of the human genome is regulated by interferons (INFs). Interferon stimulated genes can act as an initial response to pathogen invasion, slowing down viral replication and increasing expression of immune signaling complexes. There are three known types of interferon. With approximately 450 genes highly expressed in response to interferon type I. Type I interferon consists of INF-α, INF-β, INF-ω and is expressed in response to viral infection. ISGs induced by type I interferon are associated with viral replication suppression and increase expression of immune signaling proteins. Type II interferon consists only of INF-γ and is associated with controlling intracellular pathogens and tumor suppressor genes. Type III interferon consists of INF-λ and is associated with viral immune response and is key in anti-fungal neutrophil response.

<span class="mw-page-title-main">Fungal ribotoxin</span> Group of extracellular ribonucleases secreted by fungi

Fungal ribotoxins are a group of extracellular ribonucleases (RNases) secreted by fungi. Their most notable characteristic is their extraordinary specificity. They inactivate ribosomes by cutting a single phosphodiester bond of the rRNA that is found in a universally conserved sequence. This cleavage leads to cell death by apoptosis. However, since they are extracellular proteins, they must first enter the cells that constitute their target to exert their cytotoxic action. This entry constitutes the rate-determining step of their action.

References

  1. 1 2 3 4 5 6 7 8 Iglesias, Rosario; Pérez, Yolanda; de Torre, Carlos; Ferreras, J. Miguel; Antolín, Pilar; Jiménez, Pilar; Rojo, M. Ángeles; Méndez, Enrique; Girbés, Tomás (2005-06-01). "Molecular characterization and systemic induction of single-chain ribosome-inactivating proteins (RIPs) in sugar beet (Beta vulgaris) leaves". Journal of Experimental Botany. 56 (416): 1675–1684. doi: 10.1093/jxb/eri164 . ISSN   0022-0957. PMID   15863448.
  2. 1 2 3 4 5 Iglesias, Rosario; Pérez, Yolanda; Citores, Lucía; Ferreras, José M.; Méndez, Enrique; Girbés, Tomás (2008-04-01). "Elicitor-dependent expression of the ribosome-inactivating protein beetin is developmentally regulated*". Journal of Experimental Botany. 59 (6): 1215–1223. doi: 10.1093/jxb/ern030 . ISSN   0022-0957. PMID   18343888.
  3. 1 2 3 4 5 6 7 8 9 10 Iglesias, Rosario; Citores, Lucía; Di Maro, Antimo; Ferreras, José M. (February 2015). "Biological activities of the antiviral protein BE27 from sugar beet (Beta vulgaris L.)". Planta. 241 (2): 421–433. doi:10.1007/s00425-014-2191-2. ISSN   1432-2048. PMID   25326773. S2CID   253892668.
  4. 1 2 3 Citores, Lucía; Iglesias, Rosario; Gay, Carolina; Ferreras, José Miguel (February 2016). "Antifungal activity of the ribosome-inactivating protein BE27 from sugar beet ( Beta vulgaris L.) against the green mould Penicillium digitatum: Antifungal activity of the N -glycosylase BE27". Molecular Plant Pathology. 17 (2): 261–271. doi:10.1111/mpp.12278. PMC   6638414 . PMID   25976013.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.