| Perl Molson 2005-09-24, 1:31 pm |
| Isolation and partial characterization of an antiviral, RC-183, from
the edible mushroom Rozites caperata.
Piraino F, Brandt CR.
Department of Ophthalmology and Visual Sciences, university of
Wisconsin Medical School, Madison 53706-1532, USA.
A protein of 10,425 Da was purified from the edible mushroom Rozites
caperata and shown to inhibit herpes simplex virus types 1 and 2
replication with an IC50 value of < or = 5 microM. The protein
designated RC-183 also significantly reduced the severity of HSV-1
induced ocular disease in a murine model of keratitis, indicating in
vivo efficacy. HSV mutants lacking ribonucleotide reductase and
thymidine kinase were also inhibited, suggesting the mechanism does not
involve these viral enzymes. Antiviral activity was also seen against
varicella zoster virus, influenza A virus, and respiratory syncytial
virus, but not against adenovirus type VI, coxsackie viruses A9 and B5,
or human immunodeficiency virus. Characterization of RC-183 by mass
spectroscopy, sequencing, and other methods suggests it is composed of
a peptide (12 or 13 mer) coupled to ubiquitin via an isopeptide bond
between the c-terminal glycine of ubiquitin and the epsilon amino group
of a lysine residue in the peptide. The peptide sequence did not match
any known sequence. Thus, RC-183 is a novel antiviral that may have
clinical utility or serve as a lead compound for further development.
Determining the mechanism of action may lead to identification of novel
steps in viral replication.
http://www.ncbi.nlm.nih.gov/entrez/...9&dopt=Abstract
Ubiquitin
>From Wikipedia, the free encyclopedia.
Ubiquitin is a small protein that occurs in all eukaryotic cells. Its
main function is to mark other proteins for destruction, known as
proteolysis. Several ubiquitin molecules attach to the condemned
protein (polyubiquitination), and it then moves to a proteasome, a
barrel-shaped structure where the proteolysis occurs. Ubiquitin can
also mark transmembrane proteins (for example, receptors) for removal
from the membrane.
Ubiquitin consists of 76 amino acids and has a molecular mass of about
8500 amu. It is highly conserved among eukaryotic species: Human and
yeast ubiquitin share 96% sequence identity.
Cartoon representation of ubiquitin.
Molecular surface of ubiquitin.The process of marking a protein with
ubiquitin consists of a series of steps:
Activation of ubiquitin -- the carboxyl group of the terminal glycine
of ubiquitin binds to the sulfhydryl group -SH of an
ubiquitin-activating enzyme E1. The sulfhydryl group is a cysteine
residue on the E1 protein. This step requires a ATP molecule as an
energy source and results in the formation of a thioester bond between
ubiquitin and E1.
Transfer of ubiquitin from E1 to the ubiquitin-conjugating enzyme E2
via trans(thio)esterification.
Then, the final transfer of ubiquitin to the target protein can occur
either:
directly from E2. This is primarily used when ubiquitin is transferred
to another ubiquitin already in place, creating a branched ubiquitin
chain.
or
via an E3 enzyme, which binds specifically to both E2 and the target
protein. The target protein is usually a damaged or non-functional
protein that is recognized by a destruction-targeting sequence.
Ubiquitins then bind to a lysine residue in the target protein,
eventually forming a tail of ubiquitin molecules. This is the typical
way to mark specific proteins for proteolysis.
Finally, the marked protein is digested in the 26S-proteasome into
small peptides, amino acids (usually 6-7 amino acid subunits). Although
the ubiquitins also enter the proteasome, they are not degraded and may
be used again.
The gene whose disruption causes Angelman syndrome, UBE3A, encodes an
ubiquitin ligase (E3) enzyme termed E6-AP.
The ubiquitin pathway is thought to be the method of cellular egress
for a number of retroviruses, including HIV and Ebola, but the exact
mechanism by which this occurs has yet to be deduced.
Once perceived as a system exclusively invoved in removing damaged
protein from the cell, ubiquitination and subsequent protein
degradation by the proteasome is now perceived as a universal
regulatory mechanism for signal transduction whose importance approach
protein phosphorylation. The importance of proteolytic degradation in
cell signaling has been highlighted by the discovery of the role of
ubiquitin in the proteolytic pathway which earned Aaron Ciechanover,
Avram Hershko and Irwin Rose the 2004 Nobel Prize in Chemistry.
The Anaphase-promoting complex (APC) and the SCF complex (for
Skp1-Cullin-F-box protein complex) are two examples of protein scaffold
involved in recognition and ubiquitination of specific target proteins
for degradation by the proteasome.
[edit]
Immunohistochemistry
Antibodies to ubiquitin are used in histology to identify abnormal
accumulations of protein inside cells that are markers of disease.
These accumulations are called inclusion bodies. Examples of such
abnormal inclusions in cells are
Neurofibrillary tangles in Alzheimer's disease
Lewy body in Parkinson's disease
Pick bodies in Picks disease
Inclusions in motor neuron disease
Mallory's Hyalin in alcoholic liver disease
Rosenthal fibres in astrocytes
http://en.wikipedia.org/wiki/Ubiquitin
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