Structure, Phosphorylation, and Biological Function of the HIV-1 Specific Virus Protein U (Vpu)

  • Victor Wray
  • Ulrich Schubert
Part of the Protein Reviews book series (PRON, volume 1)


Knowledge describing the structure and function of the small regulatory human immunodeficiency virus type 1 (HIV-1) viral protein U (Vpu) has increased significantly over the last decade. Vpu is an 81 amino acid class I oligomeric integral-membrane phosphoprotein that is encoded exclusively by HIV-1. It can therefore be anticipated, that Vpu might contribute to the increased pathogenic potential of HIV-1 when compared with HIV-2 that has so far had a lower impact on the acquired immune deficiency syndrome (AIDS) pandemic. Various biological functions have been ascribed to Vpu: first, in the endoplasmic reticulum (ER) Vpu induces degradation of CD4 in a process involving the ubiquitin-proteasome pathway and phosphorylation of its cytoplasmic tail. In addition, there is also evidence that Vpu interferes with major histocompatibility complex (MHC) class I antigen presentation and regulates Fas mediated apoptosis. Second, Vpu augments virus release from a post ER compartment by a cation-selective ion channel activity mediated by its transmembrane (TM) anchor. The phosphorylation of the molecule is mediated by the ubiquitous protein kinase caseinkinase 2 (CK-2) within a central conserved dodecapeptide at positions Ser52 and Ser56 located in a flexible hinge region between two helical domains. Structural information, provided experimentally mainly by solution- and solid-state nuclear magnetic resonance (NMR) spectroscopy and made possible through the availability of synthetic and recombinant material, have shown that the biological activities of Vpu are localized in two distinct domains that are mainly confined to the C-terminal cytoplasmic and N-terminal TM domains, respectively. Similar to other small viral proteins that interact with membranes Vpu is a very flexible molecule whose structure is exceptionally environment dependent. It assumes it’s most structured form in the hydrophobic environment in or at the membrane. An initial 20–23 residue α-helix in the N-terminus adopts a TM alignment while the cytoplasmic tail forms an α-helix-flexible-α-helix-turn motif, of which at least a part is bound parallel to the membrane surface. Details of the arrangement of oligomeric forms of the molecule that are presumably required for the ion channel activity, are emerging from recent theoretical calculations, while this particular function is currently the area of pharmaceutical interest.


Nuclear Magnetic Resonance Acquire Immune Deficiency Syndrome Nuclear Magnetic Resonance Spectroscopy Endoplasmic Reticulum Degradation Phosphoacceptor Site 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. Aldrovandi, G.M., and Zack, J.A. (1996). Replication and pathogenicity of human immunodeficiency virus type 1 accessory gene mutants in SCID-hu Mice. J. Virol. 70, 1505–1511.PubMedGoogle Scholar
  2. Barre-Sinoussi, F., Cherman, J.C., Rey, F., Nugeyre, M.T., Chamaret, S., Gruest, J. et al. (1983). Isolation of a T-lympohotropic retrovirus from a patient at risk for acquired immunodeficiency syndrome (AIDS). Science 220, 868–870.PubMedCrossRefGoogle Scholar
  3. Buck, M. (1998). Trifluoroethanol and colleagues: Cosolvents come of age. Recent studies with peptides and proteins. Q. Rev. Biophys. 31, 297–355.PubMedCrossRefGoogle Scholar
  4. Brünger, A.T. (1992). X-PLOR, Version 3.1, A system for X-ray crystallography and NMR. Yale University Press, New Haven and London.Google Scholar
  5. Casella, C.R., Rapaport, E.L., and Finkel, T.H. (1999). Vpu increases susceptibility of human immunodeficiency virus type 1-infected cells to fas killing. J. Virol. 73, 92–100.PubMedGoogle Scholar
  6. Chen, M.Y., Maldarelli, F., Karczewski, M.K., Willey, R.L., and Strebel, K. (1993). Human immunodeficiency virus type 1 Vpu protein induces degradation of CD4 in vitro: The cytoplasmic domain of CD4 contributes to Vpu sensitivity. J. Virol. 67, 3877–3884.PubMedGoogle Scholar
  7. Coadou, G., Evrard-Todeschi, N., Gharbi-Benarous, J., Benarous, R., and Girault, J.P. (2002). HIV-1 encoded virus protein U (Vpu) solution structure of the 41–62 hydrophilic region containing the phosphorylated sites Ser52 and Ser56. Int. J. Biol. Macromol. 30, 23–40.PubMedCrossRefGoogle Scholar
  8. Cohen, E.A., Terwilliger, E.F., Sodroski, J.G., and Haseltine, W.A. (1988). Identification of a protein encoded by the vpu gene of HIV-1. Nature 334, 532–534.PubMedCrossRefGoogle Scholar
  9. Cordes, F.S., Tustian, A.D., Sansom, M.S., Watts, A., and Fischer, W.B. (2002). Bundles consisting of extended transmembrane segments of Vpu from HIV-1: Computer simulations and conductance measurements. Biochemistry 41, 7359–7365.PubMedCrossRefGoogle Scholar
  10. Ewart, G.D., Mills, K., Cox, G.B., and Gage, P.W. (2002). Amiloride derivatives block ion channel activity and enhancement of virus-like particle budding caused by HIV-1 protein Vpu. Eur. Biophys. J. 31, 26–35.PubMedCrossRefGoogle Scholar
  11. Ewart, G.D., Sutherland, T, Gage, P.W., and Cox, G.B. (1996). The Vpu protein of human immunodeficiency virus type 1 forms cation-selective ion channels. J. Virol. 70, 7108–7115PubMedGoogle Scholar
  12. Federau, T., Schubert, U., Flossdorf, J., Henklein, P., Schomburg, D., and Wray, V. (1996). Solution structure of the cytoplasmic domain of the human immunodeficiency virus type 1 encoded virus protein U (Vpu). Int. J. Pept. Protein Res. 47, 297–310.PubMedCrossRefGoogle Scholar
  13. Fischer, W.B. and Sansom, M.S. (2002). Viral ion channels: Structure and function. Biochim. Biophys. Acta 1561, 27–45.PubMedCrossRefGoogle Scholar
  14. Friborg, J., Ladha, A. Goettlinger, H., Haseltine, W.A., and Cohen, E.A. (1995). Functional analysis of the phosphorylation sites on the human immunodeficiency virus type 1 Vpu protein. J. Acquired Immune Def. Syndr. Hum. Retrovir. 8, 10–22.Google Scholar
  15. Fujita, K., Omura, S., and Silver, J. (1997). Rapid degradation of CD4 in cells expressing HIV-1 Env and Vpu is blocked by proteasome inhibitors. J. Gen. Virol. 78, 619–625.PubMedGoogle Scholar
  16. Gonzalez, M.E. and Carrasco, L. (1998). The human immunodeficiency virus type 1 Vpu protein enhances membrane permeability. Biochemistry 37, 13710–13719.PubMedCrossRefGoogle Scholar
  17. Henklein, P., Schubert, U., Kunert, O., Klabunde, S., Wray, V., Kloppel, K.D. et al. (1993). Synthesis and characterization of the hydrophilic C-terminal domain of the human immunodeficiency virus type 1-encoded virus protein U (Vpu). Pept. Res. 6, 79–87.PubMedGoogle Scholar
  18. Henklein, P., Kinder, R., Schubert, U., and Bechingerm, B. (2000). Membrane interactions and alignment of structures within the HIV-1 Vpu cytoplasmic domain: Effect of phosphorylation of serines 52 and 56. FEBS Lett. 482, 220–224.PubMedCrossRefGoogle Scholar
  19. Ho Park, S., Mrse, A.A., Nevzorov, A.A., Mesleh, M.F., Oblatt-Montal, M., Montal, M. et al. (2003). Three-dimensional structure of the channel-forming transmembrane domain of virus protein “u” (Vpu) from HIV-1. J. Mol. Biol. 333, 409–424.CrossRefGoogle Scholar
  20. Huet, T., Cheynier, R., Meyerhans, A., Roelants, G., and Wain-Hobson, S. (1990). Genetic organization of a chimpanzee lentivirus related to HIV-1. Nature 345, 356–359.PubMedCrossRefGoogle Scholar
  21. Kanki, P.J., Travers, K.U., MBoup, S., Hsieh, C.C., Marlink, R.G., Gueye-Ndiaye, A. et al. (1994). Slower heterosexual spread of HIV-2 than HIV-1. Lancet 343, 943–946.PubMedCrossRefGoogle Scholar
  22. Klimkait, T., Strebel, K., Hoggan, M.D., Martin, M.A., and Orenstein, J.M. (1990). The human immunodeficiency virus type 1-specific protein vpu is required for efficient virus maturation and release. J. Virol. 64, 621–629.PubMedGoogle Scholar
  23. Kerkau, T., Bacik, I., Bennink, J.R., Yewdell, J.W., Hunig, T. et al. (1997). The human immunodeficiency virus type 1 (HIV-1) Vpu protein interferes with an early step in the biosynthesis of major histocompatibility complex (MHC) class I molecules. J. Exp. Med. 185, 1295–1305.PubMedCrossRefGoogle Scholar
  24. Kukol, A. and Arkin, I.T. (1999). Vpu transmembrane peptide structure obtained by site-specific fourier transform infrared dichroism and global molecular dynamics searching. Biophys J. 77, 1594–1601.PubMedGoogle Scholar
  25. Lama, J., Mangasarian, A., and Trono, D. (1999). Cell-surface expression of CD4 reduces HIV-1 infectivity by blocking Env incorporation in a Nef-and Vpu-inhibitable manner. Curr. Biol. 9, 622–631.PubMedCrossRefGoogle Scholar
  26. Lamb, R.A. and Pinto, L.H. (1997). Do Vpu and Vpr of human immunodeficiency virus type 1 and NB of influenza B virus have ion channel activities in the viral life cycles? Virology 229, 1–11.PubMedCrossRefGoogle Scholar
  27. Li, J.T., Halloran, M., Lord, C.I., Watson, A., Ranchalis, J., Fung, M. et al. (1995). Persistent infection of macaques with simian-human immunodeficiency viruses. J. Virol. 69, 7061–7067.PubMedGoogle Scholar
  28. Lopez, C.F., Montal, M., Blasie, J.K., Klein, M.L., and Moore, P.B. (2002). Molecular dynamics investigation of membrane-bound bundles of the channel-forming transmembrane domain of viral protein U from the human immunodeficiency virus HIV-1. Biophys. J. 83, 1259–1267.PubMedGoogle Scholar
  29. Ma, C., Marassi, F.M., Jones, D.H., Straus, S.K., Bour, S., Strebel, K. et al. (2002). Expression, purification, and activities of full-length and truncated versions of the integral membrane protein Vpu from HIV-1. Protein Sci. 11, 546–557.PubMedCrossRefGoogle Scholar
  30. Maldarelli, F., Chen, M.-Y., Willey, R.L., and Strebel, K. (1993). Human immunodeficiencyvirus type 1 Vpu protein is an oligomeric type 1 integral membrane protein. J. Virol. 67, 5056–5061PubMedGoogle Scholar
  31. Marassi, F.M., Ma, C., Gratkowski, H., Straus, S.K., Strebel, K., Oblatt-Montal, M. et al. (1999). Correlation of the structural and functional domains in the membrane protein Vpu from HIV-1. Proc. Natl. Acad. Sci. USA 96, 14336–14341.PubMedCrossRefGoogle Scholar
  32. Margottin, F., Bour, S.P., Durand, H., Selig, L., Benichou, S., Richard, V. et al. (1998). A novel human WD protein, h-beta TrCp, that interacts with HIV-1 Vpu connects CD4 to the ER degradation pathway through an F-box motif. Mol. Cell 1, 565–574.PubMedCrossRefGoogle Scholar
  33. Marlink, R., Kanki, P., Thior, I., Travers, K., Eisen, G., Siby, T. et al. (1994). Reduced rate of disease development after HIV-2 infection as compared to HIV-1. Science 265, 1587–1590.PubMedCrossRefGoogle Scholar
  34. Miller, R. and Sarver, N. (1997). HIV accessory proteins as therapeutic targets. Nature Med. 3, 389–394.PubMedCrossRefGoogle Scholar
  35. Niefind, K. and Schomburg, D. (1991). Amino acid similarity coefficients for protein modelling and sequence alignment derived from main chain folding angles. J. Mol. Biol. 219, 481–497.PubMedCrossRefGoogle Scholar
  36. Paul, M. and Jabbar, M.A. (1997). Phosphorylation of both phosphoacceptor sites in the HIV-1 Vpu cytoplasmic domain is essential for Vpu-mediated ER degradation of CD4. Virology 232, 207–216.PubMedCrossRefGoogle Scholar
  37. Schubert, U., Anton, L.C., Bacik, I., Cox, J.H., Bour, S., Bennink, J.R. et al (1998). CD4 glycoprotein degradation induced by human immunodeficiency virus type 1 Vpu protein requires the function of proteasomes and the ubiquitin conjugating pathway. J. Virol. 72, 2280–2288.PubMedGoogle Scholar
  38. Schubert, U., Bour, S., Ferrer-Montiel, A.V., Montal, M., Maldarelli, F., and Strebel, K. (1996a). The two biological activities of human immunodeficiency virus type 1 Vpu protein involve two separable structural domains. J. Virol. 70, 809–819.PubMedGoogle Scholar
  39. Schubert, U., Ferrer-Montiel, A.V., Oblatt-Montal, M., Henklein, P., Strebel, K., and Montal, M. (1996b). Identification of an ion channel activity of the Vpu transmembrane domain and its involvement in the regulation of virus release from HIV-1-infected cells. FEBS Lett. 398, 12–8.PubMedCrossRefGoogle Scholar
  40. Schubert, U., Henklein, P., Boldyreff, B., Wingender, E., Strebel, K., and Porstmann, T. (1994). The human immunodeficiency virus type 1 encoded Vpu protein is phosphorylated by casein kinase-2 (CK-2) at positions Ser52 and Ser56 within a predicted alpha-helix-turn-alpha-helix-motif. J. Mol. Biol. 236, 16–25.PubMedCrossRefGoogle Scholar
  41. Schubert, U., Schneider, T., Henklein, P., Hoffmann, K., Berthold, E., Hauser, H. et. al. (1992). Human-immunodeficiency-virus-type-1-encoded Vpu protein is phosphorylated by casein kinase II. Eur. J. Biochem. 204, 875–883.PubMedCrossRefGoogle Scholar
  42. Schubert, U. and Strebel, K. (1994). Differential activities of the human immunodeficiency virus type-1 encoded Vpu protein are regulated by phosphorylation and occur in different cellular compartments. J. Virol. 68, 2260–2271.PubMedGoogle Scholar
  43. Sramala, I., Lemaitre, V., Faraldo-Gomez, J.D., Vincent, S., Watts, A., and Fischer, W.B. (2003). Molecular dynamics simulations on the first two helices of Vpu from HIV-1. Biophys. J. 84, 3276–3284.PubMedGoogle Scholar
  44. Strebel, K., Klimkait, T., and Martin, M.A. (1988). A novel gene of HIV-1, vpu, and its 16-kilodalton product. Science 241, 1221–1223.PubMedCrossRefGoogle Scholar
  45. Strebel, K., Klimkait, T., Maldarelli, F., and Martin, M.A. (1989). Molecular and biochemical analyses of human immunodeficiency virus type 1 vpu protein. J. Virol. 63, 3784–3791.PubMedGoogle Scholar
  46. Vincent, M. J. and Jabbar, M.A. (1995). The human immunodeficiency virus type 1 Vpu protein: A potential regulator of proteolysis and protein transport in the mammalian secretory pathway. Virology 213, 639–649.PubMedCrossRefGoogle Scholar
  47. Willbold, D., Hoffmann, S. and Rosch, P. (1997). Secondary structure and tertiary fold of the human immunodeficiency virus protein U (Vpu) cytoplasmic domain in solution. Eur. J. Biochem. 245, 581–588.PubMedCrossRefGoogle Scholar
  48. Wray, V., Federau, T., Henklein, P., Klabunde, S., Kunert, O., Schomburg, D. et al. (1995). Solution structure of the hydrophilic region of HIV-1 encoded virus protein U (Vpu) by CD and 1H NMR spectroscopy. Int. J. Pept. Protein Res. 45, 35–43.PubMedCrossRefGoogle Scholar
  49. Wray, V., Kinder, R., Federau, T., Henklein, P., Bechinger, B., and Schubert, U. (1999). Solution structure and orientation of the transmembrane anchor domain of the HIV-1-encoded virus protein U by high-resolution and solid-state NMR spectroscopy. Biochemistry 38, 5272–5282.PubMedCrossRefGoogle Scholar
  50. Wüthrich, K. (1986). NMR of Proteins and Nucleic Acids. Wiley, New York.Google Scholar
  51. Yao, X.J., Garzon, S., Boisvert, F., Haseltine, W.A., and Cohen, E.A. (1993). The effect of vpu on HIV-1-induced syncytia formation. J. Acq. Immune. Defic. Syndr. 6, 135–141.Google Scholar
  52. Zheng, S., Strzalka, J., Ma, C., Opella, S.J., Ocko, B.M., and Blasie, J.K. (2001). Structural studies of the HIV-1 accessory protein Vpu in langmuir monolayers: Synchrotron X-ray reflectivity. Biophys. J. 80, 1837–1850.PubMedCrossRefGoogle Scholar

Copyright information

© Kluwer Academic/Plenum Publishers, New York 2005

Authors and Affiliations

  • Victor Wray
    • 1
  • Ulrich Schubert
    • 2
  1. 1.Department of Structural BiologyGerman Research Centre for BiotechnologyBraunschweigGermany
  2. 2.Institute for Clinical and Molecular VirologyUniversity of Erlangen-NürnbergErlangenGermany

Personalised recommendations