Filament polymorphism

STRUCTURE, FUNCTION, AND AMYLOIDOGENESIS OF FUNGAL PRIONS FILAMENT POLYMORPHISM AND PRION VARIANTS... 

B. Relationship Between Filament Polymorphism and Prion Variants. .. 167... 

In many amyloid systems, filament polymorphism has been observed by EM (e.g., Goldsbury et al., 1997, 2000). Structural variations may be expressed in terms of long-range axial repeats (Goldsbury et al, 2005 Jimenez et al., 2001), diameter (Louis et al., 2005), and/or number of protofilaments (Jimenez et al., 2002). Solid-state NMR has also been used to detect slight structural differences in Alzheimer s /1-peptide filaments... 

Baxa, U., Cassese, T., Kajava, A. V., and Steven, A. C. (2006). Structure, function, and amyloidogenesis of fungal prions Filament polymorphism and prion variants. Adv. Protein Chem. 73, 125-180. 

Sylvestre, P. Couture-Tosi, E. Mock, M. Polymorphism in the collagen-like region of the Bacillus anthracis BclA protein leads to variation in exosporium filament length. /. Bacteriol. 2003,185,1555-1563. 

Kozuka, J., Yokota, H., Arai, Y., Ishii, Y. and Yanagida, T. (2006). Dynamic polymorphism of single actin molecules in the actin filament. Nat. Chem. Biol. 2, 83-6. 

Fig. 12. Polymorphism of filaments formed from the fusion protein constructs Ure2p1-65-GFP, Ure2p1 85-GFP, Ure2p1-90-GFP, and Ure2p1 95-GFP is illustrated with representative negatively stained micrographs of filaments. The panels are labeled (in white), according to the construct from which each filament was made. In projection, the filaments have a sinusoidal form whose wavelength is constant within a given filament but varies from filament to filament. The filament shown at top left is a double filament, consisting of two single filaments wrapped around each other. Bar = 200 nm.

Polymorphism also seems to influence the growth rate of filaments. In their AFM study of Sup35pNM filaments involving a compilation of the growth rates measured on many in dividual filaments, DePace and Weissmann (2002) found different classes, for example, fast on both ends, slow at one end, and so on (Section V.A Fig. 8). They were able to show in several rounds of growth analysis that growth rate is an intrinsic property for each class of filaments. 

Unfortunately, the description of amyloid fibrils given above is simplistic since in vitro self-assembly of amyloid peptides and proteins yields polymorphic structures, as has been commonly observed in the past for other protein assemblies such as actin filaments (Millonig et al, 1988) and intermediate filaments (Herrmann and Aebi, 1999). On the one hand, assembly polymorphism complicates the characterization of fibril structure. On the other hand, it offers some insight into fibril formation. For this reason a more rational understanding of amyloid fibril formation at the molecular level is a key issue in the field of amyloidosis. 

Herrmann, H., and Aebi, U. (1999). Intermediate filament assembly Temperature sensitivity and polymorphism. Cell. Mol. Life Sd. 55, 1416-1431. 

Gharieb, M. M., Wilkinson, S. C. Gadd, G. M. (1995). Reduction of selenium oxyanions by unicellular, polymorphic and filamentous fungi cellular location of reduced selenium and implications for tolerance. Journal of Industrial Microbiology, 14, 300-11. 

Parry, D. A. D., and Steinert, P. M. (1999). Intermediate filaments Molecular architecture, assembly, dynamics and polymorphism. Quart. Rev. Biophys. 32, 99-187. 

Much is known about the steps in the biochemical reaction of ATP breakdown by myosin and how these relate to the production of force by the crossbridge. However, since it is no longer attached to the myosin thick filament, myosin SI cannot be an adequate model for a strained crossbridge. Thus data from muscle fibers (e.g., the dependence of phosphate affinity on strain) must also be considered. In this review we attempt to summarize the currently known structural data on myosin and produce a synthesis of this with the biochemical data. We start with an analysis of the polymorphism of the myosin crossbridge and relate this to the crossbridge cycle proposed by Lymn and Taylor (1971). 

Helical symmetry The polymeric proteins of filamentous viruses and the cytoskel-ton possess helical symmetry, in which subunits are related by a translation, as well as a rotational component. Actin, myosin, tubulin and various other fibrous proteins all interact with helical symmetry, which is often called screw symmetry. Screw symmetry, which relates the positions of adjacent subunits, combines a translation along the helix axis with the rotation. Actin forms a two-stranded helix of globular actin subunits. However, important variations in the helix parameters occur (Egehnan et al, 1982). The rise per subunit is relatively constant, but the twist or relative rotation around the helix axis is highly variable. This polymorphic tendency is probably important for the smooth functioning of muscle contraction, which involves considerable force generation. 

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