Triple helix rigidity

Recently it has been demonstrated, by analysis of the flexibility from conformation maps of dipeptide sequences, that the collagen triple helix contains rigid domains separated by domains with increased flexibility (see Figure 2.23) (see Silver et 2003, for a review). Autocorrelation of the peptide sequences in collagen, using Fourier analysis, demonstrates that there is a period of the flexible domains in both the molecule and... 

The size and shape of a macromolecule can be determined by measuring the physical properties of isolated macromolecules in solution. Large rigid macromolecules that are derived from extended structures including the collagen triple helix result in rodlike rigid or semirigid structures. The size, shape, and physical parameters for macromolecules discussed in this book... 

Not all large molecules are spherical they can also be long random coils with a certain degree of flexibility along the chain. If the chain is flexible, there are rapid local fluctuations between monomers and the dipole-dipole interactions are effectively averaged. An example of this is polyuridylic acid (poly U), which has a molecular weight of 100,000 daltons but is nonetheless very flexible. The line widths for poly U as a random coil are only a few hertz. If the chain is incorporated into a rigid double or triple helix, these local motions are lost and the resonances are broadened beyond detection (see Section 14.7.2). 

Nucleic acid polymers are known to undergo transitions between single strands and double and triple helices. These transitions are readily detected by NMR because of the large differences in the line widths of a flexible random coil compared to a rigid helix. A mixture of adenosine, a mononucleoside, and poly U, a large single-stranded polymer, is known to form a triple helix at low temperatures.6 The down-... 

The molecule of collagen has the form of a rigid rod ( ) with a length of 2900 A and a diameter of 12.5 A with a molecular weight of SOOjOOO. This rod consists of three helical polypeptide chains with three parallel axes separated by 4.5 X (triple helix or tropocollagen). 

In the previous section, we introduced a genetically modified coUagen-Uke triple helix peptide F877 by recombinant technology as a rigid and monodispersed... 

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