6BBB0333 Protein Structure & Design
L6 – Protein Misfolding & Disease
Prions: abnormal proteins that can induce a misfolding of normal proteins in the brain, lading to a
variety of neurodegenerative diseases
The human prion protein exists in two forms
1. PrPC
The normal, harmless form
2. PrPSc
The abnormal, infectious form
- Has an altered 3D structure that causes it to aggregate and form insoluble clumps
The prion hypothesis
Prion diseases involve the conformational conversion of the cellular prion protein to the misfolded
pathogenic form
Template-directed misfolding
- When PrPSc comes into contact with normal PrPC, it can induce a change in the
conformation of the normal protein, causing it to convert into the abnormal, infectious form.
- Process though to be autocatalytic – it can perpetuate itself by converting more normal
proteins into the infectious form
Accumulation of PrPSc
- Over time, as more PrPC proteins are converted into PrPSc, the abnormal protein aggregates
and accumulates in the brain, forming amyloid plaques
Neurodegeneration
- Once PrPSc forms, it acts as a template to catalyse more formation of PrPSc from itself
- Accumulation of the protein aggregates disrupts normal brain function and leads to
neurodegenerative diseases
- In most cases, prion diseases in humans are sporadic, meaning PrPC spontaneously converts
to PrPSc in vivo or is transmitted in an unidentified manner
(Unconventional because involves disease transmission without involvement of genetic material like
DNA or RNA – entirely dependent on protein misfolding (protein-only hypothesis))
,6BBB0333 Protein Structure & Design
- The N-terminal portion is largely unstructured and the C-terminal region contains the folded,
globular domain. The C-terminal domain consists of three a-helices (HA, HB, and HC) and a
short b-sheet with two strands (S1 and S2).
- PrPSc has the same primary structure as PrPC but a different fold. During the conversion of
PrPC to PrPSc, the a-helix content decreases somewhat but the b-sheet content increases
greatly
- Also, whereas PrPC is protease sensitive, PrPSc contains a protease-resistant core of residues
~90–230
Prion Protein Structures
- Schematic illustration of potential structures, hypothesizing the key transition between α-
helices and β-sheets.
- Beige regions – conserved
- Red/green regions – regions that exhibit structural differences between the cellular and
infectious forms
, 6BBB0333 Protein Structure & Design
- NMR spectroscopy as method of choice to study structure
- Not exact same as what was proposed initially (image on previous page) but definitely some
beta sheet formation occurring
- A lot of the protein undetermined (dotted yellow line) – not ideal to use NMR… (must use X-
ray crystallography)
Inhibition of aggregation – insight into prion aggregation
X-ray structure of PrP with ICSM 18-Fab
- Crystal structure from 2009
- Bonded to antibody
- Some interaction between prion protein and antibody to characterize
o The interaction between them locks the structure, preventing structural transitions
to be able to visualize the PrPc protein structure
L6 – Protein Misfolding & Disease
Prions: abnormal proteins that can induce a misfolding of normal proteins in the brain, lading to a
variety of neurodegenerative diseases
The human prion protein exists in two forms
1. PrPC
The normal, harmless form
2. PrPSc
The abnormal, infectious form
- Has an altered 3D structure that causes it to aggregate and form insoluble clumps
The prion hypothesis
Prion diseases involve the conformational conversion of the cellular prion protein to the misfolded
pathogenic form
Template-directed misfolding
- When PrPSc comes into contact with normal PrPC, it can induce a change in the
conformation of the normal protein, causing it to convert into the abnormal, infectious form.
- Process though to be autocatalytic – it can perpetuate itself by converting more normal
proteins into the infectious form
Accumulation of PrPSc
- Over time, as more PrPC proteins are converted into PrPSc, the abnormal protein aggregates
and accumulates in the brain, forming amyloid plaques
Neurodegeneration
- Once PrPSc forms, it acts as a template to catalyse more formation of PrPSc from itself
- Accumulation of the protein aggregates disrupts normal brain function and leads to
neurodegenerative diseases
- In most cases, prion diseases in humans are sporadic, meaning PrPC spontaneously converts
to PrPSc in vivo or is transmitted in an unidentified manner
(Unconventional because involves disease transmission without involvement of genetic material like
DNA or RNA – entirely dependent on protein misfolding (protein-only hypothesis))
,6BBB0333 Protein Structure & Design
- The N-terminal portion is largely unstructured and the C-terminal region contains the folded,
globular domain. The C-terminal domain consists of three a-helices (HA, HB, and HC) and a
short b-sheet with two strands (S1 and S2).
- PrPSc has the same primary structure as PrPC but a different fold. During the conversion of
PrPC to PrPSc, the a-helix content decreases somewhat but the b-sheet content increases
greatly
- Also, whereas PrPC is protease sensitive, PrPSc contains a protease-resistant core of residues
~90–230
Prion Protein Structures
- Schematic illustration of potential structures, hypothesizing the key transition between α-
helices and β-sheets.
- Beige regions – conserved
- Red/green regions – regions that exhibit structural differences between the cellular and
infectious forms
, 6BBB0333 Protein Structure & Design
- NMR spectroscopy as method of choice to study structure
- Not exact same as what was proposed initially (image on previous page) but definitely some
beta sheet formation occurring
- A lot of the protein undetermined (dotted yellow line) – not ideal to use NMR… (must use X-
ray crystallography)
Inhibition of aggregation – insight into prion aggregation
X-ray structure of PrP with ICSM 18-Fab
- Crystal structure from 2009
- Bonded to antibody
- Some interaction between prion protein and antibody to characterize
o The interaction between them locks the structure, preventing structural transitions
to be able to visualize the PrPc protein structure
