PRNP (1)

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Prion Protein

• Bahaaddin Ahmed Saber

27-05-2015
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OUT LINE

• Definition
• Gene Expression of Prion protein
• Function of protein
• Diagnosis
• Disease affect by prion protein
• Treatment
• And Prevention

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Definition of Prion

• Prion A small proteinaceous infectious
  disease-causing agent that is believed to be the
  smallest infectious particle. A prion is neither
  bacterial nor fungal nor viral and contains no
  genetic material. Prions have been held
  responsible for a number of degenerative brain
  diseases, including 
• Mad cow disease, 
• Creutzfeldt-Jakob disease,
• fatal familial insomnia ,kuru, and an unusual
  form of
• hereditary dementia known as Gertsmann-Straeussler
  -Scheinker disease.

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PRNP gene

• The PRNP gene is located on the short (p) arm
  of Chromosome 20 at position 13.
• More precisely, the PRNP gene is located from
  base pair 4,686,150 to base pair 4,701,587 on
  chromosome 20.

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• What is chromosome 20?
• Humans normally have 46 chromosomes in each cell,
  divided into 23 pairs. Two copies of chromosome
  20, one copy inherited from each parent, form one
  of the pairs. Chromosome 20 spans about 63
  million DNA building blocks (base pairs) and
  represents approximately 2 percent of the total
  DNA in cells.
• Identifying genes on each chromosome is an active
  area of genetic research. Because researchers use
  different approaches to predict the number of
  genes on each chromosome, the estimated number of
  genes varies. Chromosome 20 likely contains 500
  to 600 genes that provide instructions for making
  proteins. These proteins perform a variety of
  different roles in the body.

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Function of Prion protein

• The PRNP gene provides instructions for making a
  protein called prion protein (PrP), which is
  active in the brain and several other tissues.
  Although the precise function of this protein is
  unknown, researchers have proposed roles in
  several important processes. These include the
  transport of copper into cells and protection of
  brain cells (neurons) from injury
  (neuroprotection). Studies have also suggested a
  role for PrP in the formation of synapses, which
  are the junctions between nerve cells (neurons)
  where cell-to-cell communication occurs.
• Different forms of PrP have been identified. The
  normal version is often designated PrPC to
  distinguish it from abnormal forms of the
  protein, which are generally designated PrPSc.

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• What other names do people use for the PRNP gene
  or gene products?
• AltPrP ASCR CD230 antigenCJD
• GSS. MGC26679 PRIO_HUMAN
• prion protein (p27-30) (Creutzfeldt-Jakob
  disease, Gerstmann-Strausler-Scheinker syndrome,
  fatal familial insomnia)
• PRIPPrP
• PrP27-30
• PrP33-35C
• PrPc
• PrPSc

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Disease Relation with Prion Protein

• - Creutzfeldt-Jacob disease (CJD) and variant CJD
  in humans

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Disease Relation with Prion Protein

• Scrapie ( In Sheep).

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Disease Relation with Prion Protein

• Cow Mad disease

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• Models of PrPC to PrPSc conversion. (A) The
  heterodimer model proposes that upon infection of
  an appropriate host cell, the incoming PrPSc
  (orange) starts a catalytic cascade using PrPC
  (blue) or a partially unfolded intermediate
  arising from stochastic fluctuations in PrPC
  conformations as a substrate, converting it by a
  conformational change into a new ß-sheetrich
  protein. The newly formed PrPSc (green-orange)
  will in turn convert new PrPC molecules. (B) The
  noncatalytic nucleated polymerization model
  proposes that the conformational change of PrPC
  into PrPSc is thermodynamically controlled the
  conversion of PrPC to PrPSc is a reversible
  process but at equilibrium strongly favors the
  conformation of PrPC. Converted PrPSc is
  established only when it adds onto a fibril-like
  seed or aggregate of PrPSc. Once a seed is
  presModels of PrPC to PrPSc conversion. (A) The
  heterodimer model proposes that upon infection of
  an appropriate host cell, the incoming PrPSc
  (orange) starts a catalytic cascade using PrPC
  (blue) or a partially unfolded intermediate
  arising from stochastic fluctuations in PrPC
  conformations as a substrate, converting it by a
  conformational change into a new ß-sheetrich
  protein. The newly formed PrPSc (green-orange)
  will in turn convert new PrPC molecules. (B) The
  noncatalytic nucleated polymerization model
  proposes that the conformational change of PrPC
  into PrPSc is thermodynamically controlled the
  conversion of PrPC to PrPSc is a reversible
  process but at equilibrium strongly favors the
  conformation of PrPC. Converted PrPSc is
  established only when it adds onto a fibril-like
  seed or aggregate of PrPSc. Once a seed is
  present, further monomer addition is
  acceleratedent, further monomer addition is
  accelerated.

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Diagnosis

• MRI scans of the brain
• Samples of fluid from the spinal cord (spinal
  tap)
• Electroencephalogram, which analyzes brain waves
  this painless test requires placing electrodes on
  the scalp
• Blood tests
• Neurologic and visual examinations to evaluate
  for nerve damage and vision loss

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Diagnosis

• DIAGNOSING TSEsIt can be very difficult to test
  for PrPSc because it may be present in small
  amounts and separating it out from PrPC is not
  trivial. The methods currently being used test
  dead animal tissue. There are proposed ways to
  test live animals, such as detecting Prions  in
  blood, urine or Cerebrospinal Fluid (CSI), but
  these methods are not yet in widespread use. More
  information about the differences between the
  conformations of the proteins is needed before
  these other tests can become a reality. 
• 1BioassayThe most conclusive form of testing is
  the bioassay. This test works by taking a tissue
  sample of a suspected infected animal and putting
  it into a mouse or other animal and waiting for
  the disease to develop in the model organism.
  Obviously, this is a very slow and
  labor-intensive method of testing for the
  disease. A faster form of testing, but still
  labor intensive, is Immunohestochemistry. In this
  method, antibodies that recognize  PrPSc are
  injected into brain tissue, and then observed on
  slides under a microscope for the presence of
  these antibodies . If the antibodies are present,
  then they have attached to infectious prions and
  the tissue is infectious. Because each slide must
  be examined under a microscope, this type of test
  can take time and energy that makes it hard for
  mass testing.
• 2ImmunoassayAnother type of test, the
  immunoassay, is fast and easier to complete, but
  only applicable when there are high levels of
  infectious prions subsequently, lower levels may
  go undetected. The Immunoassay works by first
  adding Protease to brain tissue, which will break
  down all the non-infectious form of prions and
  leave only infectious prions. Then, antibodies
  sensitive to prions are added to the solution.
  The antibodies used are tagged with a visual
  marker so that the presence of the prions with
  show up. Testers can also run the solution on
  a Gel and the presence bands will mean that there
  is infectious prion protein. The reason this only
  works for high levels of infectious protein is
  that although many PrPScs are resistant to
  breakdown by proteases, many are not, especially
  in the early stages of the disease (it is not
  known why this is the case). Therefore, after
  proteases have been applied to the mixture, all
  of the PrPC is broken down, and some of the PrPSc
  is broken down as well, so only a little bit
  remains. Furthermore, it is hard to find
  antibodies that will only bind to the infectious
  form when we do not know the exact conformation
  differences, so proteases are a necessary step
  before adding antibodies.

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Diagnosis

• Conformation-Dependent Immunoassay3-
  Conformation dependent Immunoassay (CDI)Finally,
  a newer method that is both quick and accurate
  for low levels of infectious protein. CDI uses
  tissue taken from a live animal mixed with a
  chemical that separates infectious from
  non-infections prions based on their
  conformations. Next, an antibody tagged with
  flourescence is added to the separated area, and
  if the tissue same contains infectious protein,
  the antibody will fluoresce . 
• 4- Brain Imaging is another diagnostic
  tool that can be used for humans, but is not
  applicable to diagnosing animals that may be fed
  to humans. Furthermore, brain scans are
  expensive, and would probably only be used if
  someone is showing symptoms of aTSE, which often
  means the disease is very advanced. The
  development of a wider diagnostic test that could
  be applied to anyone who might be at risk of a
  TSE would be incredibly valuable because it might
  be easier to slow down in an early stage of the
  disease (Committee on Transmissible Spongiform
  Encephalopathies, 2004).

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• 5- Protein Misfolding Cyclic Amplification (PMCA)
• One of the obstacles to creating a test that does
  not require brain tissue, as all of the above
  tests do, is the low level of prions in other
  tissues. Formulating a blood or urine test would
  require a means of amplifying the infectious
  protein to levels that are detectable. This is
  difficult because since it is only protein,
  polymerase chain reaction (a very efficient
  method for amplifying nucleic acids) is not
  applicable. However, there is a method being
  developed that may allow an amplification process
  that would make a blood test more feasible. This
  amplification process is called  Protein
  Misfolding Cyclic Amplification (PMCA). It has
  been shown to work experimentally by mixing
  infected prions with normal prions. The idea
  behind it is that infectious prions transform
  normal prions into infectious prions, so the
  normal prions are there for the infectious to
  work on changing. However, often the infectious
  prions form clumps, so they less actively change
  the normal prion conformations. Therefore, this
  method uses sonication-pulses of sound waves-to
  break up infectious prion clumps so that they
  will spread throughout the tissue mix and
  transform the normal prions. This seems to work
  as a method of amplifying infectious protein.
  Another possible way to get around the low levels
  of infectious protein is to detect a "surrogate
  marker" instead of the protein itself. There may
  be other proteins or molecules that indicate the
  presence of the infectious prion protein that are
  easier to detect, and could therefore act as a
  "surrogate marker" because they, instead of
  prions, could be tested for in tissue. Another
  obstacle is how to distinguish among the
  different strains of TSEs. Knowing this could be
  integral to determining the source of the disease
  (inherited, spontaneous, transmitted) and to
  inventing with more targeted ways of dealing with
  the different strains disease (Committee on
  Transmissible Spongiform Encephalopathies,
  2004). 

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protein misfolding cyclic amplification machine
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Symptoms of Prion disease

• Rapidly developing dementia
• Difficulty walking and changes in gait
• Hallucinations
• Muscle stiffness
• Confusion
• Fatigue
• Difficulty speaking

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Treatment

• Prion diseases can't be cured, but certain
  medications may help slow their progress. Medical
  management focuses on keeping people with these
  diseases as safe and comfortable as possible
  despite progressive and debilitating symptoms.
• 1- Quinacrine
• 2-Pentosan polysuphate (PPS)
• 3-Tetracyclic Compounds
• 4-Flupirtine
• 5-Potential Treatments (Immunotherapy)

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• Thanks for your
  Attention