Protein amyloid self assembly: nucleation, growth, and breakage

Transcription

1 CMMP11, Manchester December 011 Protein amyloid self assembly: nucleation, growth, and breakage Chiu Fan Lee 1, Létitia Jean, and David J. Vaux 1 Max Planck Institute for the Physics of Complex Systems Dunn School of Pathology, University of Oxford

2 Protein amyloids Amyloid fibrils are linear aggregates of proteins IAPP Many proteins form amyloids Many amyloid related diseases, e.g., Alzheimer s, Parkinson, Type II diabetes Amyloid fibrils form easily in vitro Lopes et al. (007) Biophys. J µm

3 Plan Nucleation of amyloid fibrils Dynamics of fibril elongation Thermal breakage

4 A Paradox In vitro observations: experiments [monomer] 1 1 Time Expt 1: Medium [monomer] -> medium [monomer] Expt : High [monomer] -> low [monomer] Nucleation pathway: monomer -> micelle -> nucleus (fibril) Lomakin, Teplow, Kirschner and Benedek (1997) PNAS 94, 794

5 A second critical conc. Observable pathway: monomer -> micelle -> nucleus (fibril) Amount fibril Critical micellar concentration (CMC) micelle CFC monomer Time Lomakin, Teplow, Kirschner and Benedek (1997) PNAS 94, 794 Lee (009) PRE 80, 0319

6 A second critical conc. Observable pathway: monomer -> micelle -> nucleus (fibril) Amount Critical micellar concentration (CMC) CFC [monomer] CMC micelle CFC fibril 1 1 monomer Time Lomakin, Teplow, Kirschner and Benedek (1997) PNAS 94, 794 Lee (009) PRE 80, 0319

7 Interfacial effect [monomer] [Fibril] Fibrilization assay [IAPP] = 1.3µM CMC 1 & 1 Time 1 Expt 1: with Air-Water Interface (AWI), Expt : no AWI, Jean, Lee, Lee, Shaw and Vaux (010) FASEB Journal 4, 309

8 Two fibrilization pathways Adsorption layer Monomer AWI No AWI [IAPP] = 1.3µM 1 Micelle [Fibril] Fibril nucleus

9 Fibril Elongation Elongation rate ~ 1 monomer/sec Aβ single fibril elongation rate from TIRF experiment [Ban et al. JMB (004)] Monomer conc. Question: Can we explain the time scale observed?

10 Coarse-grained molecular dynamics simulations Side chain C α N C N C C α N Side chain Diffusion in rugged energy landscape [Zwanzig, PNAS ( 88)] ) # D eff = Dexp! "E & + % ( * + $ k B T ',. -. Separate monomer & fibril # correct hydrogen bonds Misalignment leads to many local minima Monomer fibrillized Lee, Loken, Jean and Vaux (009) Physical Review E 80,

11 Thermal Breakage M beads connected by springs in 1D dx ζ = f ( x) + ζk BT g( t) dt Friction coefficient -ΔE Multidimensional Kramers escape theory: b Breakage rate: R = 8ΔE b ζ 3/ πk M B T exp [ ΔE / k T] B Lee (009) Phys. Rev. E 80,

12 Breakage Profile Lee (009) Phys. Rev. E 80,

13 Summary Protein amyloids are physiologically and technologically important Heterogeneous nucleation Interface dominated at low concentration Slow dynamics of fibril elongation Diffusion in a rugged energy landscape due to misalignment Thermal breakage Multidimensional Kramers problem Uniform breakage propensity for free fibrils Tethered points break half as often

14 Thanks Oxford s Dunn School of Pathology (experiments) Catherine Davison Chongsoo Lee Michael Shaw Oxford s Particle Physics Sub-Department (grid computation infrastructure) James Loken Rhys Newman Jeff Tseng

15 Thank you! References L. Jean, C.F. Lee, C. Lee, M. Shaw and D.J. Vaux (010) Competing discrete interfacial effects are critical for amyloidogenesis. FASEB Journal 4, C.F. Lee (009) Self-assembly of protein amyloid: A competition between amorphous and ordered aggregation. Physical Review E 80, 0319 C.F. Lee, J. Loken, L. Jean and D.J. Vaux (009) Elongation dynamics of amyloid fibrils: a rugged energy landscape picture. Physical Review E 80, C.F. Lee (009) Thermal breakage of a discrete one-dimensional string. Physical Review E 80,