Oligomer globular

Alzheimer s Disease. Figure 1 A(3 monomers can self-associate to form dimers, trimers and higher oligomers. Globular structures of synthetic A(342 are known as A(3-derived diffusible ligands (ADDLs) (3-12-mers of A(3). These structures are similar to the smallest protofibrils and represent the earliest macromolecular assembly of synthetic A(3. The characteristic amyloid fiber exhibits a high beta-sheet content and is derived in vitro by a nucleation-dependent self-association and an associated conformational transition from random to beta-sheet conformation of the A(3 molecule. Intermediate protofibrils in turn self-associate to form mature fibers. 

In the case of human amylin and Afi our understanding of the diversity in amyloid fibril architecture is the result of a recursive process, since the early morphological observations were followed by assessment of the assembly pathway which in turn yielded a better understanding of fibril polymorphism. However, this structural knowledge is secondary compared to the discovery of small oligomers, globular oligomers, and early protofibrils that appear to be extremely cytotoxic (Hartley etal., 1999 Lambert et al, 1998 Walsh et al, 1999). 

Coiled coils are frequently used to form oligomers of fibrous and globular proteins... 

The leucine zipper DNA-binding proteins, described in Chapter 10, are examples of globular proteins that use coiled coils to form both homo- and heterodimers. A variety of fibrous proteins also have heptad repeats in their sequences and use coiled coils to form oligomers, mainly dimers and trimers. Among these are myosin, fibrinogen, actin cross-linking proteins such as spectrin and dystrophin as well as the intermediate filament proteins keratin, vimentin, desmin, and neurofilament proteins. 

Using the phase diagramms the data on the formation of poly(methacrylic acid) (matrix)-poly(ethylene ycol) (oligomer) complexes were interpreted - and it was shown that the prcxluction of compact globular structures of the complexes is possible only for the cxxupkd matrix PMAA and when the critical length of oli mer is reached. 

Very recently, this approach was met with success, and a series of novel ferrocene-oligomers 69-72 and polyferrocenyl peptide 73 were reported (Scheme 12.17).61 Preliminary measurements on the polymeric material indicate a globular structure in aqueous solution and a surprisingly high molecular weight. However, the polymeric material still awaits its full characterization, in particular with respect to its electronic properties. 

Interest in dendrimers is predicated in large part on the belief that size, shape, and composition matter. Dendrimers are synthetic polymers that— theoretically—are perfectly branched from a common core, giving rise to descriptions of two-dimensional representations that include tree-like or snowflake-like . As the products of synthesis, the size and composition of a dendrimer can be manipulated by choice of the starting materials. Commonly, triazines can reach protein-sized dimensions with an onset of globular structure. Larger triazine dendrimers that can reach the dimensions of small viruses have been reported. The literature is replete with examples of small dendrimers that can be viewed as floppy, randomly coiled oligomers. 

Computation reveals when dendrimers transition from small-mol-eeule oligomers to globular arehiteetures. 

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