Large T antigen

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Large T antigen
Large T antigen
according to PDB  5TCT , with a central DNA double helix (from above)
other names

Large T antigen

Existing structural data : PDB  1EJL , PDB  1GH6 , PDB  1N25

Mass / length primary structure 708 amino acids , 81,582 Da
Secondary to quaternary structure Dodecamer
Identifier
External IDs
Enzyme classification
EC, category 3.6.4.-

The large T antigen (LT LTAG or from Engl. Large , large 'and tumor antigen) is an oncogenic and DNA-binding protein of the Simian virus 40 (SV40). It is in biochemistry and cell biology for immortalization of mammalian - cells used. Homologs occur in other polyomaviruses , with lengths between 600 and 800 amino acids .

properties

The large T antigen is used by SV 40 to regulate viral replication . It also transforms the host cell . It is formed as a replication-relevant protein at the beginning of the viral replication cycle (in contrast to the capsid proteins ) and is essential for viral replication.

The large T antigen causes dormant cells to divide by overcoming the cell's checkpoints . It binds to pRB (synonym RB1) and p53 and causes the dissociation of the elongation factor E2F1 from pRB, whereby the gene expression of E2F1-regulated genes of the S phase is initiated. Binding to pRB and p53 produces the transforming effect. While researching the large T antigen, p53 was discovered in 1979.

In addition, the large T antigen inhibits the binding of p53 to DNA , as a result of which p53 is inhibited from activating gene expression . The large T antigen acts analogously to TAF (TFIID-associated factor) in initiating transcription for all three cellular RNA polymerases by stabilizing the TBP-TFIIA protein complex on promoters . It also inhibits the HDAC1 -mediated deacetylation of histones , which activates transcription. It also promotes the activation of the cyclin A promoter via its J protein domain . Presumably it inhibits the growth-inhibiting effect of the E3 ubiquitin ligase Cul7 . The 17kT isoform of the large T antigen causes RBL2 to break down and thus promotes cell growth . It binds divalent zinc ions and is glycosylated , acetylated and phosphorylated .

In the genome of the SV40 large T antigen binds at two adjacent sites of the replication origin of SV40 (SV40 ori of English. Origin of replication ). The displacement of the replication fork is formed by a helicase - activity mediated large T antigen. By stabilizing TBP and TFIIA, the large T antigen activates the transcription of the late viral mRNA .

In addition to immortalization and transformation, the large T antigen leads to disturbed differentiation , loss of DNA repair and instability of the karyotype .

structure

Large T antigen with bound p53

The large T-antigen has four different conserved protein domains linked by unstructured regions: the J-domain (a chaperone of the DnaJ type ), the ori-binding domain (OBD), the zinc-binding domain (for the formation of dodecamers of the large T antigen composed of two hexameric rings) and the AAA + type ATPase . The zinc-binding domain and the ATPase together form the helicase in the dodecameric form, which binds to the origin of replication of the viral DNA via the OBD. The ATPase provides the energy for the helicase through the hydrolysis of adenosine triphosphate (ATP). Uniquely for AAA + type ATPases, it also separates the double strands of the viral DNA.

Both the unstructured regions and the J domain serve protein-protein interactions with cellular proteins. The J domain binds to HSP70 representatives. The ATPase binds to topoisomerase 1 and p53. The Ori-binding domain is used for protein-DNA interactions with the non-coding control region in the SV40 genome and binds to replication protein A and Nbs1 . Some of the large T antigens of the polyomaviruses have an essential sequence of unclear function at the C terminus , which is phosphorylated. In the first unstructured area there is a signal sequence for transport into the cell nucleus .

In some polyomaviruses, the homologues of the large T antigen are formed by alternative splicing in a truncated form without a zinc-binding domain and without an ATPase domain, which is only involved in the transformation and not in the replication. The large T antigen has the same first 80 amino acids as the small T antigen. In the murine polyomavirus (MPyV) and some other polyomaviruses (but not SV40) the middle T antigen is also formed. The mechanisms of transformation by T antigens of polyomaviruses are different. The small T antigen enhances the transformation of the cell by the large T antigen.

Polyomaviruses are classified based on the DNA sequence of the large T antigen. However, phylogenetics differs when examining the capsid protein.

Web links

Individual evidence

  1. ^ Y. Katakura, S. Alam, S. Shirahata: Immortalization by gene transfection. In: Methods in cell biology. Volume 57, 1998, pp. 69-91, ISSN  0091-679X . PMID 9648100 .
  2. ↑ MI Maqsood, MM Matin, AR Bahrami, MM Ghasroldasht: Immortality of cell lines: challenges and advantages of establishment. In: Cell biology international. Volume 37, number 10, October 2013, pp. 1038-1045, doi : 10.1002 / cbin.10137 , PMID 23723166 .
  3. ↑ a b c d e f g h P. An, MT Sáenz Robles, JM Pipas: Large T antigens of polyomaviruses: amazing molecular machines. In: Annual review of microbiology. Volume 66, 2012, pp. 213-236, doi : 10.1146 / annurev-micro-092611-150154 , PMID 22994493 .
  4. ↑ D. Ahuja, MT Sáenz-Robles, JM Pipas: SV40 large T antigen targets multiple cellular pathways to elicit cellular transformation. In: Oncogene . Volume 24, Number 52, November 2005, pp. 7729-7745, doi : 10.1038 / sj.onc.1209046 , PMID 16299533 .
  5. ↑ J. Cheng, JA DeCaprio, MM Fluck, BS Schaffhausen: Cellular transformation by Simian Virus 40 and Murine Polyoma Virus T antigens. In: Seminars in cancer biology. Volume 19, number 4, August 2009, pp. 218-228, doi : 10.1016 / j.semcancer.2009.03.002 , PMID 19505649 , PMC 2694755 (free full text).
  6. ^ DP Lane, LV Crawford: T antigen is bound to a host protein in SV40-transformed cells. In: Nature . Volume 278, Number 5701, March 1979, pp. 261-263, PMID 218111 .
  7. ^ DI Linzer, AJ Levine: Characterization of a 54K dalton cellular SV40 tumor antigen present in SV40-transformed cells and uninfected embryonal carcinoma cells. In: Cell . Volume 17, Number 1, May 1979, pp. 43-52, PMID 222475 .
  8. ↑ a b Large T antigen - Simian virus 40 (SV40). In: Uniprot .org. June 20, 2018, accessed May 3, 2018 .
  9. ↑ CD Toouli, LI Huschtscha, AA Neumann, JR Noble, LM Colgin, B. Hukku, RR Reddel: Comparison of human mammary epithelial cells immortalized by simian virus 40 T-Antigen or by the telomerase catalytic subunit. In: Oncogene . Volume 21, Number 1, January 2002, pp. 128-139, doi : 10.1038 / sj.onc.1205014 , PMID 11791183 .
  10. ↑ W. Lilyestrom, MG Klein, R. Zhang, A. Joachimiak, XS Chen: Crystal structure of SV40 large T antigen bound to p53: interplay between a viral oncoprotein and a cellular tumor suppressor. In: Genes & development. Volume 20, number 17, September 2006, pp. 2373-2382, doi : 10.1101 / gad.1456306 , PMID 16951253 , PMC 1560412 (free full text).
  11. ^ D. Topalis, G. Andrei, R. Snoeck: The large tumor antigen: a "Swiss Army knife" protein possessing the functions required for the polyomavirus life cycle. In: Antiviral research. Volume 97, Number 2, February 2013, pp. 122-136, doi : 10.1016 / j.antiviral.2012.11.007 , PMID 23201316 .
  12. ↑ U. Moens, M. Van Ghelue, M. Johannessen: Oncogenic potentials of the human polyomavirus regulatory proteins. In: Cellular and molecular life sciences: CMLS. Volume 64, Number 13, July 2007, pp. 1656-1678, doi : 10.1007 / s00018-007-7020-3 , PMID 17483871 .
  13. ↑ M. Van Ghelue, MT Khan, B. Ehlers, U. Moens: Genome analysis of the new human polyomaviruses. In: Reviews in medical virology. Volume 22, Number 6, November 2012, pp. 354-377, doi : 10.1002 / rmv.1711 , PMID 22461085 .
  14. ↑ MM Fluck, BS Schaffhausen: Lessons in signaling and tumorigenesis from polyomavirus middle T antigen. In: Microbiology and molecular biology reviews: MMBR. Volume 73, Number 3, September 2009, pp. 542-63, Table of Contents, doi : 10.1128 / MMBR.00009-09 , PMID 19721090 , PMC 2738132 (free full text).
  15. ↑ G. Stakaitytė, JJ Wood, LM Knight, H. Abdul-Sada, NS Adzahar, N. Nwogu, A. Macdonald, A. Whitehouse: Merkel cell polyomavirus: molecular insights into the most recently discovered human tumor virus. In: Cancers. Volume 6, number 3, June 2014, pp. 1267–1297, doi : 10.3390 / cancers6031267 , PMID 24978434 , PMC 4190541 (free full text).
  16. ↑ Study Group of the International Committee on Taxonomy of Viruses , S. Calvignac-Spencer, MC Feltkamp, ​​MD Daugherty, U. Moens, T. Ramqvist, R. Johne, B. Ehlers: A taxonomy update for the family Polyomaviridae. In: Archives of virology. Volume 161, Number 6, June 2016, pp. 1739-1750, doi : 10.1007 / s00705-016-2794-y , PMID 26923930 .
  17. ↑ CB Buck, K. Van Doorslaer, A. Peretti, EM Geoghegan, MJ Tisza, P. An, JP Katz, JM Pipas, AA McBride, AC Camus, AJ McDermott, JA Dill, E. Delwart, TF Ng, K. Farkas, C. Austin, S. Kraberger, W. Davison, DV Pastrana, A. Varsani: The Ancient Evolutionary History of Polyomaviruses. In: PLoS pathogens. Volume 12, number 4, April 2016, p. E1005574, doi : 10.1371 / journal.ppat.1005574 , PMID 27093155 , PMC 4836724 (free full text).