Atomic force microscopy under controlled conditions reveals structure of C-terminal region of α-synuclein in amyloid fibrils

ACS Nano. 2012 Jul 24;6(7):5952-60. doi: 10.1021/nn300863n. Epub 2012 Jun 20.

Abstract

Atomic force microscopy (AFM) is widely used to measure morphological and mechanical properties of biological materials at the nanoscale. AFM is able to visualize and measure these properties in different environmental conditions. However, these conditions can influence the results considerably, rendering their interpretation a matter of some subtlety. We demonstrate this by imaging ~10 nm diameter α-synuclein amyloid fibrils, focusing specifically on the structure of the C-terminal part of the protein monomers incorporated into fibrils. Despite these influences leading to variations in fibril heights, we have shown that by maintaining careful control of AFM settings we can quantitatively compare the morphological parameters of fibrils imaged in air or in buffer conditions. From this comparison we were able to deduce the semiflexible character of this C-terminal region. Fibril height differences measured in air and liquid indicate that the C-terminal region collapses onto the fibril core upon drying. The fibril heights decrease upon increasing ion concentration in solution, suggesting that the C-terminal tails collapse into more compact structures as a result of charge screening. Finally, PeakForce QNM measurements show an apparent heterogeneity of C-terminal packing along the fibril length.

MeSH terms

  • Amino Acid Substitution
  • Amyloid / chemistry*
  • Amyloid / ultrastructure
  • Humans
  • Microscopy, Atomic Force / methods
  • Models, Molecular
  • Mutant Proteins / chemistry
  • Mutant Proteins / genetics
  • Mutant Proteins / ultrastructure
  • Nanotechnology
  • Parkinson Disease / genetics
  • Parkinson Disease / metabolism
  • Protein Multimerization
  • Recombinant Proteins / chemistry
  • Recombinant Proteins / genetics
  • Recombinant Proteins / ultrastructure
  • alpha-Synuclein / chemistry*
  • alpha-Synuclein / genetics
  • alpha-Synuclein / ultrastructure

Substances

  • Amyloid
  • Mutant Proteins
  • Recombinant Proteins
  • alpha-Synuclein