Protein misfolding

Overview
1. When?
  1. Protein synthesis
  2. Protein degradation
    1. Sometimes small fragments will associate with one another instead of being fully degraded
2. Why?
  1. Mutation in protein
  2. Lack of enzyme needed for correct folding
  3. Accumulated damage to protein
    1. Become less efficient
  4. Conformational changes
3. Impact
  1. Protein is non-functional
  2. Protein is lacking or in short supply
  3. Protein is in the wrong place
  4. Aggregates can accumulate and cause disruption
Aggregation and degradation
1. Type 1 procollagen
  1. Osteogenesis imperfecta
2. alpha1-antitrypsin
  1. Deficiency
3. CFTR
  1. Cystic fibrosis
    1. 1/2000 live births
    2. Autosomal recessive
    3. Epithelial plasma membrane chloride channel
      1. ABC transporter
    4. 200 different mutations
      1. May account for commonness of condition
  2. We make significantly more than we need because misfolding is so common
    1. Co-translational folding
      1. During synthesis, on the ribosome
    2. Post-translational folding
    3. F508 CFTR doesn't accumulate but is degraded in the ER
      1. The change is so minimal, but it affects the key S7-H6 loop
  3. Types of mutation
    1. Type I: No synthesis
      1. G542X
    2. Type II: Block in processing
      1. delta-F508
    3. Type III: Block in regulation
      1. Missense G551D
    4. Type IV: Altered conductance
      1. MIssense R117H
    5. Type V: Reduced synthesis
      1. MIssense A455E
4. LDL receptor
  1. Familial hypocholesterolaemia
Serpins
1. SERine Protease INhibitors
  1. alpha1-antitrypsin
    1. Mutation
      1. Emphysema
      2. Liver disease
    2. Acute-phase protein
      1. Overexpressed following mutation
    3. 1 in 20 northern Europeans heterozygous for Z-allele of alpha1-antitrypsin
      1. Loss-of-function, 60% inhibitory activity retained
        Replacement of acidic glutamine for basic lysine
        Loss of salt bridge
        Where the reactive centre loop opens up
      2. Homozygosity
        Emphysema
        Liver disease
        EM
        Filaments in "beads-on-a-string" formation
        Consistent with assembly into polymers
        PAGE
        Native runs as a ladder
        Because all different length chains have assembled
      3. Circular dichroism analysis
        Z form has less pronounced peaks and troughs
        Central aromatic residues in different environments
  2. alpha1-antichymotrypsin
  3. Antithrombin
  4. Large family
    1. Look similar
      1. Quite different roles
2. Structure well conserved
  1. 3 beta-sheets
  2. 9 alpha-helices
  3. Reactive centre loop
    1. Important for function
  4. Natively unfolded
3. Mutations
  1. Dementia
    1. Neuroserpin
4. Mechanism
  1. Cleaved by protease. Brings one side down and inserts into reactive beta sheet. Opens protein for misfolding whilst denaturing the protease
5. Polymer formation is irreversible
  1. Serpin polymers are hyperthermostable
Aggregation and accumulation
1. Amyloidoses
  1. Amyloid
    1. Insoluble fibrils that are formed by polymerisation of normally soluble proteins and are deposited in the tissues.
      1. Intra- or extracellular
    2. Smooth and not recognisable as original proteins
    3. Fibrils formed from different proteins have very similar structures
      1. Stain with Congo Red, green birefringence under cross-polarised light
        There is a particular ordering of the dye molecules
    4. EM
      1. Long
      2. Straight
      3. Unbranching
    5. X-ray
      1. Cross-beta diffraction pattern
        Repeating structure
        A ladder of beta-sheets running perpendicular to the vertical axis
  2. There are many different proteins found
    1. Extracellular
      1. Transthyretin
      2. Gelsolin
      3. Lysozyme
    2. Intracellular
      1. alpha-synuclein
      2. Tau
    3. Beta-sheet
    4. Alpha-helical
    5. Alpha/beta
    6. Peptides
    7. It's such an organised structure that it works for any size of protein
  3. Causes
    1. Mutations
      1. Transthyretin
    2. High concentration
      1. Immunoglobulin
    3. Infectious
      1. Prion
        CJD
  4. 1. Monomer
    1. 2. Aggregate
      1. 3. Oligomer
        4. Protofibril
        5. Amyloid fibril
        6. Amyloid plaque
        Protofilaments are individual fibres that wrap around one another
2. Huntingtin
  1. Huntington's disease
3. Alpha1-antitrypsin
  1. Deficiency
4. Alpha-synuclein
  1. Parkinson's
5. Cu/Zn superoxide dismutase
  1. ALS
6. Disease relates to accumulation of deposited material and disruption of tissues
  1. Cell death

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Protein misfolding

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	Created by Jen Harris over 11 years ago