Journal Club

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Journal Club
Shouyong Peng Physics Department, Boston
University July 1, 2005
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Why Study?

• Known Amyloid fibrils exibit multiple distinct
  morphologies
• (twisted or parallel assemblies of finer
  protofilaments)
• Unknown whats the origins of polymorphism?
• Two explanations are possible
• Distinct modes of lateral association of
  protofilaments w/o significant variation in
  molecular structure.
• Significant variation in molecular structure at
  protofilament level.
• Which One is Right?

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What do They do?

• On fibril structures
• Using EM and ssNMR to measure fibrils formed
  by Ab40
• On Toxicities
• Measure toxicities of different fibril
  morphologies in neuronal cell cultures.

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What They find Conclusions

• Different fibril morphologies have different
  underlying molecular structures
• The predominant structure can be controlled by
  subtle variations in fibril growth conditions
• Both morphology and molecular structure are
  self-propagating when fibrils grow from preformed
  seeds
• Different Abeta(1-40) fibril morphologies also
  have significantly different toxicities in
  neuronal cell cultures
• These results have implications for the mechanism
  of amyloid formation, the phenomenon of strains
  in prion diseases, the role of amyloid fibrils in
  amyloid diseases, and the development of
  amyloid-based nano-materials.

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Formation of fibrils with diff. morphologies

• Morphology is sensitive to subtle difference in
  fibril growth condition
• Quiescent
• undisturbed in buffer for 21 to 68 days
• Agitated
• gentle circular agitation

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Fig.1 TEM images of fibrils

• 3 to 8 days with seeds
• (sonicated fragments)

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Different morphologies

• Quiescent condition
• ?Fibrils with Periodical twist
• twist period 50 to 200 nm
• max. width 12/-1 nm
• Agitated condition
• ?Filaments with no resolvable twist
• width 5.5/-0.5 nm
• ?filaments form lateral dimers/multimers

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Fig.2 2D ssNMR of fibrils
13C labeling of all carbon sites in amino acid
residues F20,D23,V24,K28, G29,A30,and I31. Red
Cr1/Cd cross peaks of I31 Blue Cb/Cr cross
peaks of V24 Green Ca/Cb cross peaks of
F20,D23,V24,K28, and I31

• Different at molecular level !

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Different lateral association

• Suggests?
• Different amino acid side chains are exposed to
  the fibril surface
• Possibly leading to ?
• Different biological activities.

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Fig. 3 Toxicity

• Different in toxicity !

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Specific common structure features

• Intermolecular distance 0.55/-0.05 nm at V12,
  V39, and A30
• ? in-register, parallel beta-sheet for both
  morphologies

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Specific different structure features

• Quiescent
• E22 K16 side chain coupling
• ? possible E22 K16 Salt-bridge
• Agitated
• Cr pf D23 side chain N of K28
• (0.32/0.02 nm)
• ? Salt-bridge between D23-K28

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Fig.4c Mass per length
Agitated Quiescent
MPL of one-layer Ab40 (4.3kD) is 9.1kD/nm ? 2
layer for agitated fibrils 3 layers for
quiescent fibrils Not precise integer multiples
of 9.1 ? Nonzero angle between HB and fibril axis

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Conclusions

• Different fibril morphologies have different
  underlying molecular structures
• The predominant structure can be controlled by
  subtle variations in fibril growth conditions
• Both morphology and molecular structure are
  self-propagating when fibrils grow from preformed
  seeds
• Different Abeta(1-40) fibril morphologies also
  have significantly different toxicities in
  neuronal cell cultures
• These results have implications for the mechanism
  of amyloid formation, the phenomenon of strains
  in prion diseases, the role of amyloid fibrils in
  amyloid diseases, and the development of
  amyloid-based nano-materials.