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Definition
Human immunodeficiency virus (HIV) is a lentivirus that causes acquired immunodeficiency syndrome (AIDS), a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections. Over 5000 HIV-related peptides have been synthesized, that inhibit different stages of viral life cycle.

Discovery
In 1983, two separate researchers Robert Gallo and Luc Montagnier independently declared that a novel retrovirus infecting AIDS patients. Several HIV related peptides including peptides (15-mers or 20-mers) of HIV glycoprotein 160 (gp160), gp120W16D, MN envelope (env) consensus B tat, consensus B VIF, HXB2 gag, SIVmac239, SIVmac239env, SIVmac239 gag have been used to study HIV life cycle. C34 peptide of Gp41 HIV Fragment is known as HR2, belongs to the helical region of gp41 of HIV, C-terminal heptad repeat 2 (HR2) defined as C helix or C peptide. It is known that HIV-1 enters cells by membrane fusion, C34 gp41 peptide is a potent inhibitors of HIV-1 fusion 1,2. The 86 amino acid trans-activator (Tat) protein of human immunodeficiency virus type 1 (HIV-1) is an RNA-binding transcriptional regulator. HIV-1 Tat proteins (wild type and Thr40Lys mutant) and the HIV-1 Tat peptide fragments Tat(32–48) and Tat(32–72) were chemically synthesized and used for HIV studies 3.

HIV (gp120) fragment (254-274), this fragment with sequence homology to a domain of the external envelope glycoprotein (gp120) of the human immunodeficiency virus (HIV) is important for HIV infectivity and antibody neutralization 4. HIV (gp120) fragment (421-438), derived from the CD4 attachment region of HIV gp120, inhibited the syncytial formation in vitro 5. HIV-1 gag protein p17 (76-84), HLA-A*0201-restricted immunodominant CD8 epitope of the HIV gag protein used for the characterization of CD8+ -T cells of HIV-positiv patients 6. HIV-1 rev protein (34-50), this arginine-rich fragment interacts specifically with RNA. It has been shown that rev protein and rev protein (34-50) bind IIB RNA with a similar dissociation constant of approx. 10 nM 7.

Structural Characteristics
The HIV type-1 belongs to the family Retroviridae and consists of two basic components: a core of ribonucleic acid (RNA), called the genome, and a protein component that surrounds the genome, called a capsid. The single-stranded RNA is tightly bound to nucleocapsid proteins and enzymes needed for the morphogenesis of the virion such as reverse transcriptase, proteases, ribonuclease and integrase. A matrix composed of the viral protein that surrounds the capsid. Viral envelope is composed of two layers of fatty molecules taken from the membrane of a human cell during budding process. There are 70 copies of a complex HIV protein that protrudes through the surface of the virus particle, known as Env, consists of a cap, glycoprotein (gp) 120, and a stem, gp41 molecules. This glycoprotein complex is important for fusion of virus to host cell. Both these surface proteins are important targets for treatments or HIV vaccines 8.

Mode of Action
HIV binds to a CD4 receptor and one of two co-receptors on the surface of a CD4+ T- lymphocyte. After fusion, the virus releases RNA, its genetic material, into the host cell. An HIV enzyme called reverse transcriptase converts the single- stranded HIV RNA to double-stranded HIV DNA. The newly formed HIV DNA enters the host cell's nucleus. The integrated HIV DNA is called provirus. The provirus may remain inactive for several years, producing few or no new copies of HIV. When the host cell receives a signal to become active, the provirus uses a host enzyme called RNA polymerase to create copies of the HIV genomic material, as well as shorter strands of RNA called messenger RNA (mRNA). The mRNA is used as a blueprint to make long chains of HIV proteins. An HIV enzyme called protease cuts the long chains of HIV proteins into smaller individual proteins. As the smaller HIV proteins come together with copies of HIV's RNA genetic material, a new virus particle is assembled. The newly assembled virus buds out from the host cell. During budding, the new virus acquires part of the cell's outer envelope. This envelope is embedded with viral glycoproteins which are necessary for host cell recognition.

Functions

CD8 cytotoxic, HIV-1 specific CD8 cytotoxic T lymphocyte (CTL) responses play a critical role in controlling HIV-1 replication. TCR avidity correlates with CTL function, and CTLs expressing TCRs with high avidity for their cognate MHC-viral peptide complex play an important in vivo role in neutralizing virus infections, terminating virus infection and delaying systemic AIDS virus dissemination from the mucosal inoculation site.

HIV-1 envelope transmembrane protein that contain highly positively charged amphipathic helices (designated LLP) in have both cytolytic and calmodulin (CaM) binding/inhibitory properties that contribute to cytopathogenesis during a viral infection.

HIV-1 vif, The human immunodeficiency virus type 1 (HIV-1) auxiliary gene vif is essential for virus propagation in peripheral blood lymphocytes, macrophages, and in some T-cell lines. (i) Vif protein binds HIV-1 PR (protease), but not covalently linked tethered PR-PR; (ii) the four amino acids residing at the N terminus of HIV-1 PR are essential for Vif/PR interaction; (iii) synthetic peptide derived from the N terminus of HIV-1 PR inhibits Vif/PR binding; and (iv) this peptide inhibits the propagation of HIV-1 in restrictive cells 9.

References

1.     Bianchi E, Finotto M, Ingallinella P, Hrin R, Carella AV, Hou XS, Schleif WA, Miller MD, Geleziunas R, Pessi A (2005). Covalent stabilization of coiled coils of the HIV gp41 N region yields extremely potent and broad inhibitors of viral infection. PNAS., 102(36):12903-12908

2.     de Rosny E, Vassell R, Jiang S, Kunert R, Weiss CD (2004). Binding of the 2F5 monoclonal antibody to native and fusion-intermediate forms of human immunodeficiency virus type 1 gp41: implications for fusion-inducing conformational changes. J. Virol., 78(5):2627-2631.

3.     Klostermeier D, Bayer P, Kraft M, Frank RW, Rösch P (1997). Spectroscopic investigations of HIV-1 trans-activator and related peptides in aqueous solutions. Biophysical Chemistry, 63(2):87-96.

4.     Ho DD, Kaplan JC, Rackauskas IE, Gurney ME (1988). Second conserved domain of gp120 is important for HIV infectivity and antibody neutralization. Science, 239(4843):1021-1023.

5.     Morrow WJ, Williams WM, Whalley AS, Ryskamp T, Newman R, Kang CY, Chamat S, Köhler H, Kieber-Emmons T (1992). Synthetic peptides from a conserved region of gp120 induce broadly reactive anti-HIV responses. Immunology, 75(4):557-564.

6.     Wilkinson J, Cope A, Gill J, Bourboulia D, Hayes P, Imami N, Kubo T, Marcelin A, Calvez V, Weiss R, Gazzard B, Boshoff C, Gotch F (2002). Identification of Kaposi's sarcoma-associated herpesvirus (KSHV)-specific cytotoxic T-lymphocyte epitopes and evaluation of reconstitution of KSHV-specific responses in human immunodeficiency virus type 1-Infected patients receiving highly active antiretroviral therapy. J. Virol., 76(6):2634-2640.

7.     Kjems J, Calnan BJ, Frankel AD, Sharp PA (1992). Specific binding of a basic peptide from HIV-1 Rev. EMBO J., 11(3):1119-29.

8.     Chan DC, Fass D, Berger JM, Kim PS (1997). Core structure of gp41 from the HIV   envlope glycoprotein . Cell, 89:263–73.

9.     Hutoran M, Britan E, Baraz L, Blumenzweig I, Steinitz M, Kotler M (2004). Abrogation of Vif function by peptide derived from the N-terminal region of the human immunodeficiency virus type 1 (HIV-1) protease. Virology, 330(1):261-270.

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