Amyloid fibril assembly, stability, and disassembly

If amyloid fibrils and other self-assembling polypeptide systems are to be developed as new materials and components for nanotechnology and biomedicine, it is important that we understand the pathways and kinetics of their assembly. It will also be desirable to be able to control this assembly and any subsequent disassembly. 

A number of techniques can be used to monitor the growth of amyloid fibrils and provide information on the kinetics of fibril assembly or disassembly. These techniques include light scattering or dye binding assays where Thioflavin T binds to the emerging fibril structure resulting in an increase in fluorescence (Krebs et al., 2005). Fourier transform infrared spectroscopy and circular dichroism can be used to monitor a change in secondary structure as the polypeptide adopts a (3-sheet-rich confirmation (Nilsson, 2004) and a quartz crystal oscillator used to follow an increase in fibril mass as a function of time (Knowles et al., 2007). 

Complementary microscopy techniques can be used to follow the morphology and growth of fibrils either on a surface or in aliquots taken from the assembly solution including total internal reflection fluorescence microscopy (TIRFM) (Ban et al., 2004), transmission electron microscopy (TEM), or atomic force microscopy (AFM). 

Fibril formation is a nucleated process that is characterized by an initial lag phase (Devlin et al., 2006 Hortschansky et al., 2005). Nucleation is followed by a fibril growth phase known as elongation. The assembly kinetics then plateau as the majority of polypeptide is incorporated into fibrillar structures. The final portion of polypeptide incorporated into fibrils is characteristic to a particular fibril system and can vary from low conversions to greater than 99% of all protein in the sample (Gras et al., 2008). 

Seeding is one way of potentially controlling what is typically an uncontrolled fibril assembly process, where polypeptide building blocks are combined in solution under favorable conditions. Seeds are short fibril fragments that can nucleate fibril growth, eliminate the lag phase, and 

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