Helical coil

Coiled-coil helices usually have one stripe of residues engaged in knobs-into-holes interactions. There are, however, instances where a helix may engage in such interactions along two stripes (Cohen and Parry, 1990 Walshaw and Woolfson, 2003 Walshaw et ah, 2001). For example, helices of four-stranded coiled coils make their primary knobs-into-holes contacts... 

Fig. 1. Structure of spectrin superfamily proteins. Modular domains within each protein are clearly defined. Shaded spectrin repeats represent coiled coils involved in dimerization events incomplete repeats represent proportionally the number of coiled-coil helices contributed by a- and /3-spectrin when generating a complete spectrin repeat during formation of the spectrin tetramer. The dashed lines indicate how two spectrin heterodimers interact to form a functional spectrin tetramer. Asterisks in the dystrophin spectrin repeats represent the position of the two greater repeats in dystrophin with respect to utrophin, which in all other respects has a similar overall structure. Numbers in the EF hand regions represent the number of EF hand motifs.

A coiled coil is a protein bundle of 2-5 alpha helices wrapped around each other into a superhelix, also called a supercoil (Lupas, 1996a Mason and Arndt, 2004 Lupas and Gruber, 2005). In the simplest form of coiled coil, helical domains of two proteins wind around one another and bind via a distinctive knobs-into-holes pattern whereby an amino acid side chain of one helix (knob) inserts into a space surrounded by four side chains of the facing helix (hole) as first suggested by Francis Crick in 1952 (Lupas, 1996a Lupas and Gruber, 2005). 

FIGURE 8.6 Dean flow formed in a coiled helical tube, where... 

It can be seen from Fig. 7 that in curved tubes, there is a drastic reduction in axial dispersion with an increase in Dean number. These studies reveal that very high Dean numbers are required to induce significant mixing in the cross-sectional plane. Saxena proposed a simple and more effective alternative to helical coils. Helical coils are very efficient in inverting the flow... 

There are no obvious structural differences between transporters from the same superfamily that function either alone or in complex vdth accessory proteins. No specific structural determinants were identified that enable a transporter to engage the accessory proteins. In contrast, periplasmic MFPs are adapted to the structural diversity of transporters. The major differences in MFPs are in the N-terminal domains and the length ofthe periplasmic coiled-coil helical regions [117]. MFPs that... 

The most common type of secondary structure is a coiled, helical conformation known as the a-helix (Figure 19.5). The a-helix has several important features. 

Closed coil helical, and C7-type stub bundle... 

A xylan has been found in Chlorophyta, Rhodophyta, and Phaeophyta (brown algae). The skeletal polysaccharide of die green algae Caulerpa, Halimeda, and Udotea is a (1 3)-j8-D-xylopyranan, coiled helically to form microfibrils. In contrast to the crystalline lattice of cellulose, which could not be penetrated by water, the helical arrangement in the )8-D-(l — 3)-linked xylan allows in the lattice considerable hydration and hydrogen bonding, and these contribute to... 

In 1951, American chemists Linus Pauling and Robert Corey suggested that proteins could exist in the shape of an a-helix, a form in which a single protein chain twists so that it resembles a coiled helical spring (see P Figure 9.6). The chain is held in the helical shape... 

Amylose has a marked tendency to adopt a single coiled helical conformation (10.26) and this has been shown to occur in the variety known as W amylose . It contains a left-handed helix with six glucose units per turn, with pitch height 8 A, and an internal channel diameter of 5 A. Both... 

Ladder, planar, dendromeric, and other macromolecular structures Isomerism that can be changed only by bond breakage Conformation scale 1-30 nm) - kinetic arrangements of chain elements in space, engendered by rotation about bonds, e.g., from trans to gauche position or vice versa, e.g., random coils, helices, and folded chains. Conformation depends on internal and external forces, e.g., interactions, a, y, P, and T, as weU as on the route used for its creation (thermodynamically nonequUibrium structures). 

Irrespective of the subtle differenee in the all-trans or trans-syn structures that PDMS possesses at a local level, its overall structure is believed to have a regular coiled helical conformation where the backbone Si-0 bonds are effectively shielded from outside influence by the umbrella-type protection afforded by the lipophilic sheath of methyl groups [35]. Since the methyl groups are nonpolar, intermolecular interactions are minimiun and this also accounts for the low melting temperature seen for poly(dimethylsiloxane) (-40 °C). 

FIGURE 6.26 Schematic diagram of gyrotrons (a) single coiled helical beam gyrotron, (b) electron trajectory of double-coil helical beam gyrotron. 

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