Amyloid fibril patterns

Amyloid fibrils form from a variety of native proteins with diverse sequences and folds. The classic method for the structural analysis of amyloid has been X-ray fiber diffraction amyloid fibrils exhibit a characteristic diffraction signature, called the cross-/) pattern. This cross-/ pattern suggested a repeating structure in which /1-sheets run parallel to the fiber axis with their constituent /1-strands perpendicular to that direction (Sunde and Blake, 1997). This diffraction signature pointed to an underlying common core molecular structure for the amyloid fibril that could accommodate diverse sequences and folds. A number of groups have proposed amyloid folds that are consistent with the experimental data and these can be linked to repeating /1-structured units. 

Fig. 1. Cross-/] structure of amyloid fibrils. (A) Cartoon representation of a cross-/] X-ray diffraction pattern. The defining features are a meridional reflection at 4.7 A and an equatorial reflection on the order of 10 A. The 4.7-A reflection is generally much brighter and sharper than the reflection at 10 A. (B) The cross-/] core structure of amyloid fibrils. Parallel /(-sheets are depicted, but the structure could equivalendy be composed of antiparallel /(-sheets or a mix of parallel and antiparallel. The 4.7-A spacing of /(-strands within each /(-sheet is parallel to the long fibril axis. The depicted 10-A sheet-to-sheet spacing actually ranges from about 5 to 14 A (Fandrich and Dobson, 2002), depending on the size and packing of amino acid side chains. Amyloid fibrils have diameters on the order of 100 A.

The notion of a common core structure has been further supported by synchrotron X-ray fiber diffraction patterns of several amyloid fibrils the patterns show common reflections in addition to those at 4.7 and 10 A (Sunde et al., 1997). Although these data give some insight into the arrangement of the amyloid fibril core, the exact molecular structure and organization of the proteins making up this common core have yet to be uniquely defined. The inherently noncrystalline, insoluble nature of the fibrils makes their structures difficult to study via traditional techniques of X-ray crystallography and solution NMR. An impressive breadth of biochemical and biophysical techniques has therefore been employed to illuminate additional features of amyloid fibril structure. 

A prime example of a Refolding model is that of the insulin protofilament (Jimenez et al., 2002). Insulin is a polypeptide hormone composed of two peptide chains of mainly o -helical secondary structure (Fig. 3A Adams et al., 1969). Its chains (21- and 30-amino acids long) are held together by 3 disulfide bonds, 2 interchain and 1 intrachain (Sanger, 1959). These bonds remain intact in the insulin amyloid fibrils of patients with injection amyloidosis (Dische et al., 1988). Fourier transform infrared (FTIR) and circular dichroic (CD) spectroscopy indicate that a conversion to jS-structure accompanies insulin fibril formation (Bouchard et al., 2000). The fibrils also give a cross-jS diffraction pattern (Burke and Rougvie, 1972). 

A cross-jS spine model was proposed for the fibril structure of human /]2-microglobulin (h/]2m) (Ivanova et al., 2004). h/I2m is a 99-amino acid serum protein with a 7-stranded /(-sandwich fold (Fig. 10A Saper et al, 1991). In patients on long-term kidney dialysis, the protein is deposited as amyloid fibrils in the joints (Floege and Ehlerding, 1996 Koch, 1992). In vitro-formed fibrils of h/)2m give a cross-/] X-ray diffraction pattern (Ivanova et al., 2004 Smith et al., 200S). Several studies have shown that segments of h/]2m form amyloid-like fibrils on their own (Ivanova et al., 2003 Jones et al., 2003 Kozhukh et al, 2002). 

Gorevic, P. D., Castano, E. M., Sarma, R., and Frangione, B. (1987). Ten to fourteen residue peptides of Alzheimer s disease protein are sufficient for amyloid fibril formation and its characteristic x-ray diffraction pattern. Biochem. Biophys. Res. Commun. 147, 854-862. 

This chapter describes the self-assembly of non-native protein fibers known as amyloid fibrils and the development of these fibrils for potential applications in nanotechnology and biomedicine. It extends an earlier review by the author on a related topic (Gras, 2007). In Section 1, the self-assembly of polypeptides into amyloid fibrils and efforts to control assembly and any subsequent disassembly are discussed. In Section 2, this review focuses on the important role of surfaces and interfaces during and after polypeptide assembly. It examines how different surfaces can influence fibril assembly, how surfaces can be used to direct self-assembly in order to create highly ordered structures, and how different techniques can be used to create aligned and patterned materials on surfaces following self-assembly. 

Amyloid fibrils show a characteristic diffraction pattern, the so called P-cross pattern (35), which is indicative of P-sheets parallel to the fibril axis with the protein strands perpendicular to the fibril s long axis (36, 37). The pattern of amyloid is characterized by reflections at 4.75 A (along the fibril axis) and 10 A (perpendicular to the fibril axis) which occur from regular repeats and stacking of monomers. 

Isobe T, Osserman EF (1974) Patterns of amyloidosis and their association with plasma cell dyscrasias, monoclonal immunc lobulins and Bence Jones proteins. N Engl J Med 290 473-477 Ivanova Ml, Gingery M, Whitson LJ, Eisenba-g D (2003) Role of the C-terminal 28 residues of beta 2-microglobulin in amyloid fibril formation. Biochemistry 42 13536-13540 Iwata K, Fujiwara T, Matsuki Y, Akutsu H, Takahashi S, Naiki H, Goto Y (2006) 3D structure of amyloid protofilaments of beta 2-micrc lobulin fragment probed by solid-state NMR. Proc Natl Acad Sci USA 103 18119-18124... 

Oyler and Tycko have demonstrated that absolute, molecular-level structural information can be obtained from solid state NMR measurements on partially oriented amyloid fibrils.In particular, it has been shown that the direction of the fibril axis relative to a carbonyl CSA tensor can be determined from MAS sideband patterns in C NMR spectra of fibrils deposited on planar substrates. Deposition of fibrils on a planar substrate creates a highly anisotropic distribution of fibril orientations (hence, CSA tensor orientations) with most fibrils lying in the substrate plane. The anisotropic orientational distribution gives rise to distorted spinning sideband patterns in MAS spectra from which the fibril axis direction can be inferred. 

That amyloid fibrils can be formed from Vl peptides was demonstrated by Glenner et al. (127) and by Linke et al. (128). Glenner et al. treated Bence Jones proteins of types k and X with pepsin in such a manner as to cleave the chains into V and C segments (129). During the incubation, precipitates formed in many of the solutions. Under the microscope some of these precipitates (nearly all from X chains) were seen to consist of fibrils resembling those of amyloid deposits. Furthermore, the X-ray diffraction pattern had a gross appearance characteristic... 

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