Fibrillization amyloids

Thus far, we have emphasized protein-ligand binding. Proteins also self-associate sometimes, self-association is simple, producing small oligomers that readily dissociate. Other times, the protein undergoes uncontrolled aggregation and ultimately forms fibrils (amyloids) that have serious consequences in human health (e.g., as in Alzheimer s disease, Parkinson s disease). 

Peptide nanospheres Amyloid-llke fibril Amyloid-like bundled network... 

Shiv]i A P, Brown F, Davies M C, Jennings K H, Roberts C J, Tendler S J B, Wilkinson M J and Williams P M 1995 Scanning tunnelling microscopy studies of p-amyloid fibril structure and assembly FEBS Lett. 371 25-8... 

Amyloid fibrils are suggested to be built up from continuous P sheet helices... 

Figure 14.7 Ribbon diagram of one subunit of the globular form of transthyretin. The p strands are labeled A to H from the amino end. Strands C and D are thought to be unfolded to produce the conformation that forms amyloid fibrils. (Adapted from C.C.F. Blake et al., /. Mol. Biol. 121 339-356, 1978.)...

Progress in deducing more structural details of these fibers has instead been achieved using NMR, electron microscopy and electron diffraction. These studies reveal that the fibers contain small microcrystals of ordered regions of the polypeptide chains interspersed in a matrix of less ordered or disordered regions of the chains (Eigure 14.9). The microcrystals comprise about 30% of the protein in the fibers, are arranged in p sheets, are 70 to 100 nanometers in size, and contain trace amounts of calcium ions. It is not yet established if the p sheets are planar or twisted as proposed for the amyloid fibril discussed in the previous section. 

Fibrous proteins are long-chain polymers that are used as structural materials. Most contain specific repetitive amino acid sequences and fall into one of three groups coiled-coil a helices as in keratin and myosin triple helices as in collagen and p sheets as in silk and amyloid fibrils. 

Blake, C., Serpell, L. Synchrotron x-ray studies suggest that the core of the transthyretin amyloid fibril is a continuous P sheet helix. Structure 4 989-998, 1996. 

Another pathway of influence in AD is the facilitation of amyloid- 3 (A 3) aggregation through an interaction with the PAS of AChE but not of BChE. Inversely, the usual BChE (and more specifically its C-terminus) was shown recently as to attenuate in vitro the formation of amyloid fibrils [4]. 

Diamant S, Podoly E, Friedler A et al (2006) Butyrylcho-linesterase attenuates amyloid fibril formation in vitro. Proc Natl Acad Sci USA 103(23) 8628-8633... 

Entry Peptide Xg X3 X4 Total charge at neutral pH Amyloid fibril formation... 

Lyim and co-workers carried out smdies of the Ap(io 35) peptide - derived from residues 10-35 of the p-amyloid responsible for Alzheimer s disease - which forms fibrils composed of parallel p-sheets [62]. The peptide was compared to its C-terminal PEG-derivatised analogue. TEM experiments showed that both formed fibrils [63] (Fig. 21) but the uranyl acetate stain was not found inside the peptide-PEG fibrils, indicating that PEG was at the outer edge of the fibril. 

Just like in coiled-coils, p-sheet secondary structure (Fig. 2) is ubiquitous in natural examples and in proteins and biomaterials. Alzheimer s disease is characterized by fibrillar amyloid plaques in the cerebral parenchyma. The insoluble amyloid fibrils are predominantly formed upon conformational switching of the 42 amino acid... 

Makin OS, Atkins E, Sikorski P et al (2005) Molecular basis for amyloid fibril formation and stability. Proc Natl Acad Sci 102 315-320... 

Slotta U, Hess S, Spiess K et al (2007) Spider silk and amyloid fibrils a structural comparison. Macromol Biosci 7 183-188... 

Figure 18.2 Production of senile plaque (S/A4 amyloid protein. Amyloid fS4 protein (/S/A4) is part of a 695, 751 or 770 amino-acid amyloid precursor protein APP. This is a transmembrane protein which is normally cleared within the fi/A4 amino acid sequence to give short 40 amino-acid soluble derivatives. It seems that under some circumstances as in Alzheimer s disease, APP is cleared either side of the fi/A4 sequence to release the 42/43 amino acid P/A4 which aggregates into the amyloid fibrils of a senile plaque (a). (See also Fig. 18.5.) Some factors, e.g. gene mutation, must stimulate this abnormal clearage leading to the deposition of P/A4 amyloid protein as plaques and tangles and the death of neurons (b)...

Yang, F. et al., Cnrcnmin inhibits formation on amyloid beta oligomers and fibrils, binds plaqnes, and rednees amyloid in vivo, J. Biol. Chem., 280, 5892, 2005. 

Neuritic or senile plaques are extracellular protein deposits of fibrils and amorphous aggregates of P-amyloid protein.11 This formed protein is central to the pathogenesis of AD. The P-amyloid protein is present in a non-toxic, soluble form in human brains. In AD, conformational changes occur that render it insoluble and cause it to deposit into amorphous diffuse plaques associated with dystrophic neuritis.14 Over time, these deposits become compacted into plaques and the P-amyloid protein becomes fibrillar and neurotoxic. Inflammation occurs secondary to clusters of astrocytes and microglia surrounding these plaques. 

Amyloid Any of a group of chemically diverse proteins that are composed of linear non-branching aggregated fibrils. 

To this list of protein misfolding diseases can be added rare familial amyloidoses in which the mutated proteins have the classic amyloid fibril congophilic birefringence and cross-(3-sheet structure (Table 3). Many of these deposits have an impact on the central nervous system (TTR, cystatin, lysozyme) as well as on other organ systems. A newly described disease, familial British dementia, is associated with the deposition of Abri, a 34 amino acid, 4 kDa peptide cleaved from a 277 amino acid precursor sequence, the last 10 amino acids of which are not normally translated [52]. Familial encephalopathy with neuroserpin inclusion bodies (FENIB) is... 

Several pathological self-polymerizing systems have been biophysi-cally characterized sufficiently to permit identification of protein or peptide species that could serve as molecular targets in a structure-activity relationship. These include transthyretin (TTR) [73-76], serum amyloid A protein (SAA) [77], microtubule-associated protein tau [78-80], amylin or islet amyloid polypeptide (IAPP) [81,82], IgG light chain amyloidosis (AL) [83-85], polyglutamine diseases [9,86], a-synuclein [47,48] and the Alzheimer s (3 peptide [87-96]. A variety of A(3 peptide assay systems have been established at Parke-Davis to search for inhibitors of fibril formation that could be therapeutically useful [97]. 

In the search for fibril formation inhibitors, the self-association to form amyloid fibrils of the A(3 peptides containing 40 and 42 amino acids can be treated as a coupled protein folding and polymerization process passing through multiple intermediate peptide species. The in vitro challenge is (1) to identify the various conformational forms and... 

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