DESCRIBE STRUCTURE OF HIV VIRUS: T.U 2058

DESCRIBE STRUCTURE OF HIV VIRUS: T.U 2058

HIV is a complex RNA virus of the genus Lentivirus within the Retroviridae family. The virus is an approximately 100nm icosahedral structure with 72 external spikes that are formed by the two major envelope glycoproteins gp120 and gp41.

Structure of HIV Virus: Cross-Section

The lipid bilayer is also studded with a number of host-cell proteins during the budding process. HIV has a characteristic dense, cone-shaped nucleocapsid composed of the core protein p24. This nucleocapsid harbours two copies of the 9.8 kb single-stranded RNA genome which are associated with the viral enzymes reverse transcriptase (RT), RNase H, integrase and protease. In addition to structural genes HIV has genes whose products contribute to the complex regulation and replication of the virus. Of particular interest is the Nef (negative factor) protein.
Deletions and mutations of this protein have been found in some HIV-infected individuals characterized as long-term non-progressors. Two major types of the AIDS virus, HIV- 1 and HIV-2, have been identified. The major serological differences reside in the surface protein gp120. HIV-1 and HIV-2 are further separated into subtypes or ‘clades’ due to the marked variability in the V3 (variable region) of the gp120 protein. Infectivity is destroyed.

Influenza Virus, Structure, Replication and Pathogenesis

ORTHOMYXOVIRUSES ( INFLUENZA VIRUSES)

-         affinity of the viruses to mucins ( myxa: mucus)

-         4 genera: influenza A, B, C viruses and thogotoviruses

-         Mutability and high frequency of genetic reassortment.
 resultant antigenic changes in viral surface gp.

-         Influenza type A antigenically highly variable and responsible for most cases of epidemic influenza.

Structure / composition

-         virion spherical, pleomorphic (80-120 nm diameter), helical nucleocapsid (9m) SS RNA, (-) sense (13.6 kb genome size) of A and B viruses with and separate segments; infection C → 7 segments lacking neuraminidase gene.

-         Segment
1→ PB₂                   4→HA             7→M₁ and M₂

      2→PB₁                        5→NP             8→NS₁ and NS₂

      3→PA                   6→NA

Schematic representation of Influenza Virus Structure

→ 9 structural proteins; one non- structural

→ NP+ viral RNA → RNP (ribonucleoprotein)
→ PB1, PB2 and PA bound to RNP and responsible for transcription and replication.
→ M1 (matrix) protein forms a shell underneath the envelope.
→ HA and NA (surface gp) determine Ag- variation and host immunity.
→ M2 protein ( ion channel) allows PH changes in the endosome.

Virology Note: Rabies Virus: Structure, Pathogenesis, and Clinical Findings

RHABDOVIRIDAE

-         enveloped, ss RNA viruses with bullet- shaped or rod- shaped morphology

-         2 genera: lyssa virus → rabies virus and vesiculovirus → vesicular stomatitis virus

RABIES VIRUS

A.     STRUCTURE / COMPOSITION

Structure of Rabies Virus

- rod or bullet- shaped (75 x 180 nm) ; one end conical, other planar ( concave).
- Membranous envelope with protruding spikes or peplomers (10 nm) which are composed of trimers of viral gp (G) spikes don’t cover the planar end.
- Beneath the envelope is the membrane or matrix (M) protein layer
- membrane may project outwards from planar end of some virion forming a bleb.
- The core of the virion consists of helical RNP ( group specific antigen).
- Genome is unsegmented, linear, ss(-)sense RNA ( 12kb, MW 4.6 X 10⁶).
- virion contain an RNA dependent RNA polymerase.

Herpes Simplex Virus, Structure,Pathogenesis, Clinical Feature and Lab Diagnosis

Herpes virus

-         Establish lifelong persistent infections / undergo periodic reactivation

-         Reactivated infection different from disease caused by primary infection.

Structure

Virion: spherical, 150-200 nm diameter ( icosahedral), 162 capsomers

Structure of Herpes Simplex Virus (HSV-1)

Envelope: derived from nuclear membrane of infected cell

-         contains viral glycoprotein spikes (8nm long)

Tegument: amorphous, asymmetric structure between capsid and envelope.

Genome: ds DNA, linear, 124-235 kbp, reiterated sequences

Proteins: 35 proteins involved in structure of virion.

-         Genome encodes atleast 100 different proteins.

Replication: nucleus, bud from nuclear membrane.

HERPES- SIMPLEX VIRUSES

-         grow rapidly and are highly cytolytic

-         latent infection in nerve cells
HSV Type I: oropharyngeal lesions / recurrent attacks of fever blisters
                      spread by contact ( infected saliva)
HSV Type II: infects genital mucosa
                       transmitted sexually, vertically

-         growth cycle – 8- 16 hours

-         genome: 150kbp; can encode atleast 70 polypeptides

-         Atleast 11 glycoproteins known.

·         gD: most potent inducer of neutralizing antibody

·        gC: c3b binding protein

·        gE: Fc receptor (IgG)

·        gG: type specific and allow for antigenic discrimination.

·        gH: involved in release of virions.