Twisted protein ribbon

Figure 4.2 This three-dimensional image of a protein shows the many twists and folds in its structure. The coils, called alpha helices, and the ribbons, called beta pleated sheets, are generally determined by the amino acid sequence of the protein and how the amino acids in different parts form weak bonds with each other. The shape of a protein is often critical for its function.

The main characteristic of tauopathies is an age-progressing hyper-phosphorylation of the tau protein which accumulates in tangles with paired helical filaments, twisted ribbons, and/or... 

Bacillus anthracis seeretes three plasmid-eneoded soluble toxin proteins colleetively referred to as anthrax toxin these are PA, LF, and EF. LF and EF funetion individually and in combination as catalytic enzymes in suseeptible host eells. In an unusual twist of nature, they both have evolved to share PA as a eommon reeeptor binding moiety for translocation into the eytosol of the host. PA is a dominant component of the three-part protein toxin seereted by B. anthracis (Liddington et ah, 1999 Petosa et ah, 1997). The mature form of PA, a seereted 735 amino aeid protein, has a molecular weight of 83 kDa. The ribbon strueture is illustrated in Figure 31.5 along with a detailed deseription of... 

Figure 14.31 A ribbon diagram of the chicken skeietai muscie protein S-1. A ribbon diagram portrays the 3-D a-heiix and other twists and turns, yieiding insight as to how the protein moves to provide iocomotion for the animai.

From the sum total of the evidence it appears that the globular proteins have a structure similar to the form of the k-m-e-f group of the fibrous proteins, that is, a helical twist with 3-6 residues per turn or 18 residues per 5 turns. However, this does not explain the compactness of the globular proteins. It appears that the polypeptide ribbons are bunched into compact globules and held by lateral linkages between the chains. 

Figure 9 Representation of the small protein, thioredoxin, in a ribbon diagram. The twisted parallel 3-structure is indicated by the arrows in the centre, with helices on the outside.

C. is almost (95%) pure cellulose. The remainder consists of fibrous nitrogen compounds (proteins), waxes and pectins, which are found on the surface (i.e., cell wall). The fiber diameter is 12-22 pm and the length of the staple fibers runs in the range of 10-60 mm depending on the type of c. The originally round fiber takes on the shape of a twisted ribbon. For details on internal morphology - cellulose. 

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