ch 4

Functions of viral proteins

protection of genome delivery of genome assembly replication interaction with host

Metastable

stable enough to protect genome but unstable enough to release it during infection

How metastability is achieved

symmetrical arrangement of identical proteins (stable) but held by non-covalent bonds (unstable)

Methods for examining viral structure

electron microscopy X-ray crystallography cryo-electron microscopy nuclear magnetic resonance (NMR)

Electron microscopy

uses negative staining with electron-dense material resolution ~50–75 Å pioneered by Helmuth Ruska

X-ray crystallography

requires crystallization of virus produces diffraction patterns structure determined by computer

Cryo-electron microscopy

freezes sample in aqueous solution to preserve native structure

Three types of particles

helical (rod-shaped) icosahedral (spherical) complex

Symmetry rules for self-assembly

identical subunit contacts non-covalent bonding assembly is reversible and error-free

Virus-like particles (VLPs)

self-assembled capsid proteins without genome used in vaccines (HBV HPV)

Helical symmetry

protein subunits interact with genome and each other to form a rod-shaped nucleocapsid

Enveloped helical viruses

all animal viruses with helical nucleocapsids are enveloped

Icosahedral symmetry

20 triangular faces forming closed shell

minimum 60 identical subunits

Spherical capsids

built from hexamers and pentamers protein numbers are multiples of 60

Large complex capsids

distinct components with specialized roles e.g. adenovirus with icosahedral shell plus fibers

Tailed bacteriophages

icosahedral head with helical tail attached at one vertex

Herpes simplex virus capsid

contains holes for DNA entry and exit

Viral envelope glycoproteins

integral membrane proteins with ectodomain (attachment, antigenic sites, fushion, and internal domain assembly w oligomeric spikes

functions or viron proties

protection and delivery of the genome, other functiosn

protection of the genome

Assembly of stable, protective protein, shell specific recognition, and packaging of nucleic acid Genome and interaction with hostel, remembering to form the envelope

delivery of the genome

Binding to external receptors of the wholesale transmission of signals that induce encoding of the Genino induction of fusion with wholesale membranes interaction with internal components of infectious cells to direct transport to the one genome to the other side

other function

interactions with cellular components for transport to intracellular sites of assemblies and ensure efficient infectious cycle

subunits or structural unit

asymmetric unit is a single folded poly peptide chain from which capsids or nuclear acids are built. They may comprise of one protein sub unit or multiple different protein sub units.

capsid or coat

The protein shell surrounding the nucleic acid genome

nucleocapsid or core

The nucleic acid protein assembled packaged within the virion he nucleic acid protein assembled packaged within the Veron used when the assembly is discreet structure particle

envelope or viral membrane

Host cell derived, lipid, bilayer, carrying most of the glycol proteins

virion

The infectious virus particle