Aggregates fibrillar

J-sheet containg Planar and aggregated fibrillar Insulin LCP chains... 

Fig. 5.118 STM images of Kevlar most clearly reveal the nature of the fibrillar hierarchy at the macromolecular level. A bundle of uniform microfibrils about 10 nm wide is observed (A) within a larger aggregated fibrillar structure unit in images taken at successively higher magnifications. Finer fibrils are also clearly seen (B). (From Sawyer et al [435] reproduced with permission.)...

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. 

Bauer, H. H., Aebi, U., Haner, M., Hermann, R., Muller, M., and Merkle, H. P. (1995). Architecture and polymorphism of fibrillar supramolecular assemblies produced by in vitro aggregation of human calcitonin./. Struct. Biol. 115, 1-15. 

In vitro, fibril formation by several proteins displays an initial lag phase, followed by a rapid increase in aggregation (reviewed in Rochet and Lansbury, 2000). Introduction of fibrillar seeds eliminates the lag phase. These cooperative aggregation kinetics suggest that fibril formation begins with the formation of a nucleus and proceeds by fibril extension. The structure of the nucleus must therefore act as a template for the protein s conformation in the fibril. As the structural requirements for templating are unclear, it is difficult to assess the consistency of the model classes with this feature of fibril formation. We have described one possible templating mechanism for the cross-/ spine of GNNQQNY (Nelson et al., 2005). 

The ultramicroscopic examination of a gelatinising sol reveals the presence of very small particles termed ultramicrons, it is assumed on the fibrillar theory that the ultramicrons aggregate to invisible threads or fibrils. As the gelatinisation proceeds the fibrils thicken and lengthen and in many cases may actually be rendered visible by powerful magnification under the microscope. The fibrils are diffused at random in the form of a felt through the material and may, as we have noted, be markedly crystalline in the filamentous, somewhat flexible in the fibrillary and distinctly mobile and flexible in the streptrococcic forms visible under the microscope. 

Figure 5.125 Structure of collagen fibers based on collagen molecule, microfibrils and fibrillar aggregation. Reprinted, by permission, from I. V. Yannas, in Biomaterials Science, B. D. Ratner, A. S. Hoffman, F. J. Schoen, and J. E. Lemons, eds., p. 86. Copyright 1996 by Academic Press.

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