Coiled coil structures functions

Nonrepetitive but well-defined structures of this type form many important features of enzyme active sites. In some cases, a particular arrangement of coil structure providing a specific type of functional site recurs in several functionally related proteins. The peptide loop that binds iron-sulfur clusters in both ferredoxin and high potential iron protein is one example. Another is the central loop portion of the E—F hand structure that binds a calcium ion in several calcium-binding proteins, including calmodulin, carp parvalbumin, troponin C, and the intestinal calcium-binding protein. This loop, shown in Figure 6.26, connects two short a-helices. The calcium ion nestles into the pocket formed by this structure. 

Perhaps the most viable short-term use for dendritic macromolecules lies in their use as novel catalytic systems since it offers the possibility to combine the activity of small molecule catalysts with the isolation benefits of crosslinked polymeric systems. These potential advantages are intimately connected with the ability to control the number and nature of the surface functional groups. Unlike linear or crosslinked polymers where catalytic sites may be buried within the random coil structure, all the catalytic sites can be precisely located at the chain ends, or periphery, of the dendrimer. This maximizes the activity of each individual catalytic site and leads to activities approaching small molecule systems. However the well defined and monodisperse size of dendrimers permits their easy separation by ultrafiltration and leads to the recovery of catalyst-free products. The first examples of such dendrimer catalysts have recently been reported... 

High molecular weight and random coil structure of protein result in more associations and thereby enhance adhesive and cohesive properties. Although these characteristics are inherent in native gluten proteins, functional properties of other proteins may be improved by chemical or thermal processing. 

Fibrinogen is a fibrous protein that was first classified with keratin, myosin, and epidermin based on its 5.1 A repeat in wide-angle X-ray diffraction patterns (Bailey et al., 1943), which was later discovered to be associated with the Q-helical coiled-coil structure. It is a glycoprotein normally present in human blood plasma at a concentration of about 2.5 g/L and is essential for hemostasis, wound healing, inflammation, angiogenesis, and other biological functions. It is a soluble macromolecule, but forms a clot or insoluble gel on conversion to fibrin by the action of the... 

Cohen, C., and Parry, D. A. D. (1990). Alpha-helical coiled-coils and bundles How to design an alpha-helical protein. Proteins Structure, Function and Genetics 7, 1-15. 

Polymer-analogous variants reach their limits in the face of insufficient rigidity of the functionalised linear polymers which can lead to undesired coiled structures. These have to re-assume a linear structure, with an attendant loss of entropy, in order to assure reaction of all the dendrons with the functional groups attached to the backbone. The dendrons are mostly added in excess in order to facilitate complete reaction, which in turn necessitates tedious purification of the products. The additional steric hindrance occurring on attachment of larger dendrons if higher generation dendrons are already located in the close... 

The fold of a protein is the way in which the regions of helix, strand and random-coil structure within its polypeptide chain are arranged in three dimensions to form its tertiary structure (see Sect. 2.1.3). This is the simplest, and yet often a very revealing, level at which the three-dimensional structures of different proteins can be compared with one another as is indicated below, such similarities may be indicators of remote evolutionary relationships, give clues to functional analogies, or insights into the processes of protein folding. 

In the enzyme above there were only three glycines and four prolines and no hydroxyproline at all. Hydroxyproline is a specialized amino acid that appears almost nowhere else and, along with proline, it establishes a very strong triply coiled structure for collagen. The glycine is necessary as there is no room in the inside of the triple coil for any larger amino acid. Functionalized amino acids are rare in collagen. 

Figured displays simulated form factors for a multiarm star polymer of varying functionality and a hard sphere [41], The high-g asymptotic behavior, characteristic of the coil structure, is absent in the latter case. A handicap in the experimental determination of P(g) is often the narrow-g range accessible by the scattering techniques that can be overcome through the combination of low-g light scattering and high-g X-ray and/or neutron scattering (utilized on the same system). Size and shape also determine the translational diffusion Dq of the nanoparticles in dilute solution, and hence Dq can prove the consistency of the scattering results.

This Chapter focuses on analyses that can be performed based solely on the primary sequence of a protein. Several rationales can be applied. Physico-chemical characteristics of individual amino acids are one basis for predictions of gross structural features. For example, particular repetitive patterns may suggest a coiled-coil structure while in general secondary structure can be predicted based on an a statistical analysis of the primary sequence. The definition of signals recognized by the cellular transport machinery allow the prediction of subcellular location. Although somewhat unsystematic such observations can provide valuable hints as to the structure and/or function of a protein. 

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