The HIV virus is the causative agent of Human Immunodeficiency Virus (HIV). It usually infects the CD4 + T Helper cell by binding to the cell membrane, this is then followed by membrane fusion; a process that allows the virus to release viral particles into the host cell. Once infected, the T-Helper cell turns into a HIV replicating cell since the viral RNA is converted into DNA by reverse transcriptase a process facilitated by the viral proteins [ CITATION bio \l 1033 ].
The double stranded viral DNA is then transported to the nucleus where it is fused with the normal host DNA by enzyme integrase. The viral DNA can persist in this stage for long periods of time; a fact that poses a challenge in the treatment of the disease.
The viral DNA then uses the host’s cellular RNA polymerase to transcribe its DNA into two RNA splices. The shorter RNA splices are transported to the cytoplasm and golgi apparatus where their message are translated into viral proteins which become part of the completed virus. The longer spices usually constitute full length viral RNA that are usually translated into the core of the new viruses.
Like any other organism, the HIV virus has evolved to comfortably survive in its environment. This can be explained by the features that the virus has adopted in order to circumvent any changes that may intend to affect it in addition to features that will allow it to survive and be propagated in the host.
In this paper, the evolution and adaptability of the HIV virus to its host is explained in length. Below is a picture of the HIV virus with the roles of its features outlined herein.
The HIV Virus (Henderson, 2005)
Roles of the HIV Virus features in host/ environmental adaptation:
1. gp 120 (docking protein)
gp 120 refers to a glycoprotein whose gene is made up of around 1500 nucleotides that code for upto 500 amino acids. Its main function is to bind to the CD4 cells in the human host. The CD4 binding site of this glycoprotein that facilitates attachment to host cell by intermolecular attractions has been found to include amino acid residues 400-430. One half of the gp120 weight is due to a carbohydrate moiety (glyco-) that forms something like a dome over the gp120 spikes. The dome prevents the glycoprotein from being recognized by the host’s immune system. As the virus and host cell adheres to one another, the gp120 binding site opens unexpectedly.
2. gp 41
gp 41 refers to the envelope protein that resides within the viral particle. It is usually halfly embedded in the membrane thus interacts with gp 120 whilst interacting with gp 41 proteins located in the viral particle. Upon interaction of the gp 120 proteins with the CD4 cells; the gp 120 changes shape simultaneously changing the shape of gp 41 thus initiating the process of membrane fusion between the cell and virus and host cell.
3. Reverse transcriptase
This enzyme is unique to retroviruses. The HIV-1 reverse transcriptase is usually composed of two molecular subunits known as p66 and p51 corresponding to their molecular weights. This enzyme usually copies the viral RNA into a complimentary DNA strand. The DNA is then integrated into the host’s DNA. Transcriptase is a major target in HIV treatment given it is hugely targeted in the use of Highly Active Antiretroviral Therapy (HAART).
P 24 is the core protein the HIV viral particle and it forms the capsid. In mature retroviruses, the capsids usually organize the genetic material for efficient replication. The capsids are made of closed hexameric arrays of viral CA protein but its high resolution structure has remained elusive [ CITATION Gan07 \l 1033 ].The blood level of p 24 protein is a direct indicator of HIV progression.
The matrix forms a major structural component of the HIV virus. The p 17 matrix protein, a product of the HIV gag gene serve structural role in the viral particle given they line the inside of the HIV envelope thus anchoring the gp 41 and gp 120 entities to the envelope. P 17 also facilitates the intrusion of the virus into the host’s nucleus. This is due to the fact that it possesses protein sequences recognized by cellular mechanisms as indicating the need for its transportation to the nucleus.
6. RNA (Ribonucleic acid)
RNA is the molecular component HIV virus uses to encode its genome. Reverse transcriptase usually synthesizes a complimentary deoxyribonucleic acid (DNA) strand from RNA prior to association with host’s DNA.
7. Lipid membrane
The membrane is a spherical layer surrounding the viral core. Like in any other cells, it is made up of lipids. Usually the p 17- the matrix protein- lines the membrane’s inner surface. On the membrane surface, spikes are anchored (forming the viral envelope). These spikes refer to the gp 120 and gp 41 proteins involved in viral cell- host cell adhesion and membrane fusion.
biologycorner.com. (n.d.). How HIV infects cells.
Ganser-Pornillos, B. K., Cheng, A., & Yeager, M. (2007). Structure of Full-Length HIV-1 CA: A Model for the Mature Capsid Lattice. Elsevier , 70-79.
Henderson), U. N. (2005). Diagram of HIV virus. US National Institute of Health (redrawn by en:User:Carl Henderson).