Fibril

Abstract: Collagen is most abundant in animal tissues as very long fibrils with a characteristic axial periodic structure. The fibrils provide the major biomechanical scaffold for cell attachment and anchorage of macromolecules, allowing the shape and form of tissues to be defined and maintained. How the fibrils are formed from their monomeric precursors is the primary concern of this review. Collagen fibril formation is basically a self-assembly process (i.e. one which is to a large extent determined by the intrinsic properties of the collagen molecules themselves) but it is also sensitive to cell-mediated regulation, particularly in young or healing tissues. Recent attention has been focused on "early fibrils' or "fibril segments' of approximately 10 microns in length which appear to be intermediates in the formation of mature fibrils that can grow to be hundreds of micrometers in length. Data from several laboratories indicate that these early fibrils can be unipolar (with all molecules pointing in the same direction) or bipolar (in which the orientation of collagen molecules reverses at a single location along the fibril). The occurrence of such early fibrils has major implications for tissue morphogenesis and repair. In this article we review the current understanding of the origin of unipolar and bipolar fibrils, and how mature fibrils are assembled from early fibrils. We include preliminary evidence from invertebrates which suggests that the principles for bipolar fibril assembly were established at least 500 million years ago.

Abstract: Publisher Summary Despite the presence of a significant amount of carbohydrate in these fibrils, the staining reaction was eventually shown to be because of the protein component. The histologic benzothiazole dyes thioflavin S (ThS) and thioflavin T (ThT) under the appropriate conditions selectively stain amyloid structures in a number of pathological settings, as does the diazobenzidine sulfonate dye, Congo red, which is also birefringent when bound to fibrils. Phorwhite BBU, Sirius Red, and several other fluorescent and nonfluorescent aromatic molecules also show this property. Investigation of the amyloid fibril formation process requires not only the ability to distinguish the characteristic amyloid B-sheet structure from amorphous aggregates of the monomer or nonamyloid fibril forms of the precursor protein, but quantitation of the amyloid form as well. Congo red and thioflavin T undergo characteristic spectral alterations on binding to a variety of amyloid fibrils that do not occur on binding to the precursor polypeptides, monomers, or amorphous aggregates of peptide. Both dyes have been adapted to in vitro measurements of amyloid fibril formation.

Abstract: In the search for the molecular mechanism of insulin fibrillation, the kinetics of insulin fibril formation were studied under different conditions using the fluorescent dye thioflavin T (ThT). The effect of insulin concentration, agitation, pH, ionic strength, anions, seeding, and addition of 1-anilinonaphthalene-8-sulfonic acid (ANS), urea, TMAO, sucrose, and ThT on the kinetics of fibrillation was investigated. The kinetics of the fibrillation process could be described by the lag time for formation of stable nuclei (nucleation) and the apparent rate constant for the growth of fibrils (elongation). The addition of seeds eliminated the lag phase. An increase in insulin concentration resulted in shorter lag times and faster growth of fibrils. Shorter lag times and faster growth of fibrils were seen at acidic pH versus neutral pH, whereas an increase in ionic strength resulted in shorter lag times and slower growth of fibrils. There was no clear correlation between the rate of fibril elongation and ionic ...