lec 4

Subunit (protien submit)

Single, folded polypeptide chain

Structural unit

Asymmetrical units.unit from which caspids or nucleoeaspiels are built; may comprise one protien subuant.

Caspid

Coat, the protein stall surrounding the nuclei's head

Nuckocaspiel

Lone, the nuekic acid-protien assembly packaged used when this assembly is a discrete substructure of a particle

Envelope

Viral membrane, the host cell-discred lipid belayer carrying viral glycoprotions

Virus particles are metastable

Must protect the genomes, come apart on infection meets a signal to disassemble

Virus particles have not attained

minimum free energy conformation, Need to surmount unfavorable energy barrier, Energy is put into virus particle during assembly, Potential energy can be used for disassembly if cell provides the proper signal (receptor, cellular condition)

Stable structure

metastability is acheived ,Symmetrical arrangement of many identical

proteins to provide maximum contact

Unstable structure

Not usually covalently bound together, Can be taken apart or loosened upon infection to release genome

Methods for examining viral structure

Electron microscopy, X-ray crystallography, Cryo-electron microscopy , Nuclear magnetic resonance spectroscopy

(NMR)

Electron microscopy

1940s, Era of modern structural virology, Helmuth Ruska, Image of bacteriophage , infecting bacteria, Need to be stained, Negative staining with electron dense material– Uranyl acetate, Phosphotungstate, Will scatter electrons, Resolution 50-75 Angstroms, Detailed structural interpretation impossible

Three types of particles

1. Helical (rod-shaped)

2. Icosahedral (spherical)

3. Complex

Building virus particles

Symmetry is essential

• Watson & Crick

• Identical protein subunits are distributed with

• Helical symmetry for rod-shaped viruses

• Icosahedral symmetry for round viruses

Symmetry rules for self-assembly

Each subunits has identical bonding contacts

with its neighbors

2. The bonding contacts are usually non-covalent

self assembly are

reversable and error free

Symmetry & self-assembly

Many capsid proteins can self-assemble into

virus-like particles (VLPs)

• HBV and HPV vaccines are VLPs made in yeast,

NO GENOME NOT INFECTIOUS , Can make body produce antibiodies

Why do we vaccinate for HPV?

orotects from cancer

Helical symmetry

Coat protein molecules engage in identical, equivalent interactions with each other & with the viral genome to form a large stable structure from a single protein subunit

Enveloped RNA viruses with (-) ssRNA & helical

nucleocapsids

paramyxoviridae(measles and mumps), rhabdoviridae(rabies), orthomyxoviridae(imfluenza), flloviridae(ebola), the nucleocapsid in the nuclear acid protien assembky that is packaged within the viron

Spherical capsids

Icosahedrons, Subunits tend to be arranged as hexamers & pentamers, All round capsids have a precise number of proteins, multiples of 60; 60, 180, 240, 960

Icosahedron

solid with 20 faces, each an equilateral triangle. Allows formation of a closed shell with a minimum of 60 identical subunits

Adeno-associated virus 2 (Parvovirus)

25 nm, 60 copies of a single capsid protein, Used for gene therapy

large complex caspids

Distinct components with different symmetries, Presence of proteins with specialized roles, Adenovirus

adenovirus

Icosahedral shell, 720 copies viral protein II

(hexon), 60 copies of protein III (penton), Other proteins interspersed throughout, Fibers at 21 vertices

Tailed bacteriophages

Icosahedral head; Tail is a complex rod, with helical symmetry, attached at one ,of 12 vertices of the capsid

Herpes simplex virus capsid contains holes for

entry an$ exit of DNA

Caspids can be covered by host membrane: enveloped virons.

E nuerope is a lipid bilaya, driven from host cells, envelope occurred by budding of neurocaspid through a cellular membrane, nucleocaspids inside the envelope may have helical } isohedial synonym

Viral envelope glycoproteins

Integral membrane glycoproteins, ectodomain, internal domain k oligomeric spikes

ectodomain

attachment antigenic sidtes, fushion

infernal domain

assembky