Structure
HIV is different in structure from other retroviruses. It is around 120 nm in diameter (around 60 times smaller than a red blood erythocyte) and roughly spherical.
HIV-1 is composed of two copies of non-covalently linked positive single-stranded RNA enclosed by a conical capsid comprising the viral protein p24, typical of lentiviruses (Figure 1). Lysine tRNA is the primer of the Magnesium dependent, reverse transcriptase. It packages two copies of its positive strand, unspliced, 5'guanosine-capped and 3'-polyadenylated RNA genome which is used for strand-transfer-mediated recombination which enables the virus to rapidly evolve under stress or pressure from the environment. The RNA component is 9749 nucleotides long. RNA genome has a 5’ cap (Gppp), a 3’ poly(A)tail, and many open reading frames (ORFs). Viral structural proteins are encoded by long ORFs, whereas smaller ORFs encode regulators of viral life cycle comprising attachment, membrane fusion, replication, and assembly. This is in turn surrounded by an envelope of host-cell origin. The single-strand RNA is tightly bound to the nucleocapsid proteins, p6, p7 and enzymes that are indispensable for the development of the virion, such as reverse transcriptase and integrase. The nucleocapsid (p7 and p6) associates with the genomic RNA (one molecule per hexamer) and protects the RNA from digestion by nucleases. A matrix composed of an association of the viral protein p17 surrounds the capsid, ensuring the integrity of the virion particle. Also enclosed within the virion particle are Vif, Vpr, Nef, p7 and viral Protease (Figure 1). The envelope is formed when the capsid buds from the host cell, taking some of the host-cell membrane with it. The envelope includes the glycoproteins gp120 and gp41.
As a result of its role in virus-cell attachment, the structure of the virus envelope spike, consisting of gp120 and gp41, is of particular importance. It is hoped that determining the envelope spike's structure will contribute to scientific understanding of the virus and its replication cycle, and help in the creation of a cure. The first model of its structure was compiled in 2006 using cryo-electron tomography and suggested that each spike consists of a trimer of three gp120–gp41 heterodimers. However, published shortly after was evidence for a single-stalk "mushroom" model, with a head consisting of a trimer gp120s and a gp41 stem, which appears as a compact structure with no obvious separation between the three monomers, anchoring it to the envelope. There are various possibilities as to the source of this difference, as it is unlikely that the viruses imaged by the two groups were structurally different. More recently, further evidence backing up the heterodimer trimer-based model has been found.
Read more about this topic: Structure And Genome Of HIV
Famous quotes containing the word structure:
“It is difficult even to choose the adjective
For this blank cold, this sadness without cause.
The great structure has become a minor house.
No turban walks across the lessened floors.
The greenhouse never so badly needed paint.”
—Wallace Stevens (1879–1955)
“What is the most rigorous law of our being? Growth. No smallest atom of our moral, mental, or physical structure can stand still a year. It grows—it must grow; nothing can prevent it.”
—Mark Twain [Samuel Langhorne Clemens] (1835–1910)
“Women over fifty already form one of the largest groups in the population structure of the western world. As long as they like themselves, they will not be an oppressed minority. In order to like themselves they must reject trivialization by others of who and what they are. A grown woman should not have to masquerade as a girl in order to remain in the land of the living.”
—Germaine Greer (b. 1939)