Biology:Vault (organelle)

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Short description: Eukaryotic organelle
Vault, N-terminal repeat domain
穹窿体.jpg
Structure of the Vault complex from rat liver.[1]
Identifiers
SymbolVault
PfamPF01505
InterProIPR002499
PROSITEPDOC51224

The vault or vault cytoplasmic ribonucleoprotein is a eukaryotic organelle whose function is not yet fully understood. Discovered and isolated by Nancy Kedersha and Leonard Rome in 1986,[2] vaults are cytoplasmic organelles which, when negative-stained and viewed under an electron microscope, resemble the arches of a cathedral's vaulted ceiling, with 39-fold (or D39d) symmetry.[1] They are present in many types of eukaryotic cells, and appear to be highly conserved among eukaryotes.[3]

Morphology

Vaults are large ribonucleoprotein particles. About 3 times the size of a ribosome and weighing approximately 13 MDa, they are found in most eukaryotic cells and all higher eukaryotes. They measure 34 nm by 60 nm from a negative stain, 26 nm by 49 nm from cryo-electron microscopy, and 35 nm by 59 nm from STEM.[4] The vaults consist primarily of proteins, making it difficult to stain with conventional techniques.

Structure

The protein structure consists of an outer shell composed of 78 copies of the ~100 kDa major vault protein (MVP). Inside are two associated vault proteins, TEP1 and VPARP. TEP1, also known as the telomerase-associated protein 1,[5] is 290 kDa and VPARP (also known as PARP4) is related to poly (ADP-ribose) polymerase (PARP) and is 193 kDa.[6] Vaults from higher eukaryotes also contain one or several small vault RNAs (vRNAs, also known as vtRNAs) of 86–141 bases within.[7]

The MVP subunits are composed head-to-head, with the N-termini of each half-vault facing each other. From the N-terminal to the C-terminal, a MVP subunit folds into 9 repeat domains, 1 band7-like shoulder domain, 1 cap-helix domain, and 1 cap-ring domain, corresponding to the shape of the vault shell. VPARP binds to repeat domain #4. TEP1, itself a ring due to the WD40 repeat, binds to the cap domain, with one particular type of vRNA plugging the cap.[8]

Function

Despite not being fully elucidated, vaults have been associated with the nuclear pore complexes and their octagonal shape appears to support this.[9][10] Vaults have been implicated in a broad range of cellular functions including nuclear-cytoplasmic transport, mRNA localization, drug resistance, cell signaling, nuclear pore assembly, and innate immunity.[11] The three vault proteins (MVP, VPARP, and TEP1) have each been knocked out individually and in combination (VPARP and TEP1) in mice.[12][13][14] All of the knockout mice are viable and no major phenotypic alterations have been observed. Dictyostelium encode three different MVPs, two of which have been knocked out singly and in combination.[15] The only phenotype seen in the Dictyostelium double knockout was growth retardation under nutritional stress.[16] If vaults are involved in essential cellular functions, it seems likely that redundant systems exist that can ameliorate their loss.

Association with cancer

In the late 1990s, researchers found that vaults (especially the MVP) were over-expressed in cancer patients who were diagnosed with multidrug resistance, that is the resistance against many chemotherapy treatments.[17] Although this does not prove that increased number of vaults led to drug resistance, it does hint at some sort of involvement. This has potential in discovering the mechanisms behind drug-resistance in tumor cells and improving anticancer drugs.[15]

Evolutionary conservation

Vaults have been identified in mammals, amphibians, avians and Dictyostelium discoideum.[3] The Vault model used by the Pfam database identifies homologues in Paramecium tetraurelia, Kinetoplastida, many vertebrates, a cnidarian (starlet sea anemone), molluscs, Trichoplax adhaerens, flatworms, Echinococcus granulosus and Choanoflagellate.[18]

Although vaults have been observed in many eukaryotic species, a few species do not appear to have the ribonucleoprotein. These include:[19]

These four species are model organisms for plants, nematodes, animal genetics and fungi respectively. Despite these exceptions, the high degree of similarity of vaults in organisms that do have them implies some sort of evolutionary importance.[3]

Homologs of the major vault protein has been computationally found in bacteria. Cyanobacterial sequences appear most similar.[20][21] Pfam is also able to identify some such homologs.[18]

Vault engineering

The Rome lab at UCLA has collaborated with a number of groups to use the baculovirus system to produce large quantities of vaults. When the major vault protein (MVP) is expressed in insect cells, vault particles are assembled on polyribosomes in the cytoplasm.[22] By using molecular genetic techniques to modify the gene encoding the major vault protein, vault particles have been produced with chemically active peptides attached to their sequence. These modified proteins are incorporated into the inside of the vault particle without altering its basic structure. Proteins and peptides can also be packaged into vaults by attachment of a packaging domain derived from the VPARP protein.[16] A number of modified vault particles have been produced in order to test the concept that vaults can be bio-engineered to allow their use in a wide variety of biological applications including drug delivery, biological sensors, enzyme delivery, controlled release, and environmental remediation.

A vault has been packaged with a chemokine for potential use to activate the immune system to attack lung cancer, and this approach has undergone phase I trials.[23][24]

See also

References

  1. ↑ 1.0 1.1 "The structure of rat liver vault at 3.5 angstrom resolution". Science 323 (5912): 384–8. January 2009. doi:10.1126/science.1164975. PMID 19150846. Bibcode: 2009Sci...323..384T. 
  2. ↑ "Isolation and characterization of a novel ribonucleoprotein particle: large structures contain a single species of small RNA". The Journal of Cell Biology 103 (3): 699–709. September 1986. doi:10.1083/jcb.103.3.699. PMID 2943744. 
  3. ↑ 3.0 3.1 3.2 "Vaults. II. Ribonucleoprotein structures are highly conserved among higher and lower eukaryotes". The Journal of Cell Biology 110 (4): 895–901. April 1990. doi:10.1083/jcb.110.4.895. PMID 1691193. 
  4. ↑ "Vaults. III. Vault ribonucleoprotein particles open into flower-like structures with octagonal symmetry". The Journal of Cell Biology 112 (2): 225–35. January 1991. doi:10.1083/jcb.112.2.225. PMID 1988458. 
  5. ↑ "Vaults and telomerase share a common subunit, TEP1". The Journal of Biological Chemistry 274 (46): 32712–7. November 1999. doi:10.1074/jbc.274.46.32712. PMID 10551828. 
  6. ↑ "The 193-kD vault protein, VPARP, is a novel poly(ADP-ribose) polymerase". The Journal of Cell Biology 146 (5): 917–28. September 1999. doi:10.1083/jcb.146.5.917. PMID 10477748. 
  7. ↑ "The vault complex". Cellular and Molecular Life Sciences 60 (9): 1828–37. September 2003. doi:10.1007/s00018-003-3030-y. PMID 14523546. 
  8. ↑ Tanaka, Hideaki; Tsukihara, Tomitake (2012). "Structural studies of large nucleoprotein particles, vaults". Proceedings of the Japan Academy, Series B 88 (8): 416–433. doi:10.2183/pjab.88.416. PMID 23060231. Bibcode: 2012PJAB...88..416T. 
  9. ↑ "Evidence that vault ribonucleoprotein particles localize to the nuclear pore complex". Journal of Cell Science 106 ( Pt 1): 23–9. September 1993. doi:10.1242/jcs.106.1.23. PMID 8270627. 
  10. ↑ "A large particle associated with the perimeter of the nuclear pore complex". The Journal of Cell Biology 93 (1): 63–75. April 1982. doi:10.1083/jcb.93.1.63. PMID 7068761. 
  11. ↑ "Vaults and the major vault protein: novel roles in signal pathway regulation and immunity". Cellular and Molecular Life Sciences 66 (1): 43–61. January 2009. doi:10.1007/s00018-008-8364-z. PMID 18759128. 
  12. ↑ "The Telomerase/vault-associated protein TEP1 is required for vault RNA stability and its association with the vault particle". The Journal of Cell Biology 152 (1): 157–64. January 2001. doi:10.1083/jcb.152.1.157. PMID 11149928. 
  13. ↑ "Telomerase-associated protein TEP1 is not essential for telomerase activity or telomere length maintenance in vivo". Molecular and Cellular Biology 20 (21): 8178–84. November 2000. doi:10.1128/mcb.20.21.8178-8184.2000. PMID 11027287. 
  14. ↑ "Disruption of the murine major vault protein (MVP/LRP) gene does not induce hypersensitivity to cytostatics". Cancer Research 62 (24): 7298–304. December 2002. PMID 12499273. 
  15. ↑ 15.0 15.1 "Vaults are the answer, what is the question?". Trends in Cell Biology 6 (5): 174–8. May 1996. doi:10.1016/0962-8924(96)10014-3. PMID 15157468. 
  16. ↑ 16.0 16.1 "Development of the vault particle as a platform technology". ACS Nano 7 (2): 889–902. February 2013. doi:10.1021/nn3052082. PMID 23267674. 
  17. ↑ "Vaults: a ribonucleoprotein particle involved in drug resistance?". Oncogene 22 (47): 7458–67. October 2003. doi:10.1038/sj.onc.1206947. PMID 14576851. 
  18. ↑ 18.0 18.1 http://pfam.xfam.org/family/PF01505 Major Vault Protein repeat Pfam family
  19. ↑ "Unlocking vaults: organelles in search of a function". Trends in Cell Biology 1 (2–3): 47–50. August 1991. doi:10.1016/0962-8924(91)90088-Q. PMID 14731565. 
  20. ↑ Daly, TK; Sutherland-Smith, AJ; Penny, D (2013). "In silico resurrection of the major vault protein suggests it is ancestral in modern eukaryotes.". Genome Biology and Evolution 5 (8): 1567–83. doi:10.1093/gbe/evt113. PMID 23887922. 
  21. ↑ Sokolskyi, Tymofii (December 12, 2019). "Bacterial Major Vault Protein homologs shed new light on origins of the enigmatic organelle". bioRxiv 10.1101/872010.
  22. ↑ "Polyribosomes are molecular 3D nanoprinters that orchestrate the assembly of vault particles". ACS Nano 8 (11): 11552–9. November 2014. doi:10.1021/nn504778h. PMID 25354757. 
  23. ↑ "CCL21 Chemokine Therapy for Lung Cancer". International Trends in Immunity 1 (1): 10–15. January 2013. PMID 25264541. 
  24. ↑ "Novel CCL21-vault nanocapsule intratumoral delivery inhibits lung cancer growth". PLOS ONE 6 (5): e18758. May 2011. doi:10.1371/journal.pone.0018758. PMID 21559281. Bibcode: 2011PLoSO...618758K. 

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