Coiled coil

[3] Many coiled coil-type proteins are involved in important biological functions, such as the regulation of gene expression — e.g., transcription factors.

Eventually, after some controversy and frequent correspondences, Crick's lab declared that the idea had been reached independently by both researchers, and that no intellectual theft had occurred.

[7][8] Based on sequence and secondary structure prediction analyses identified the coiled-coil domains of keratins.

The most favorable way for two such helices to arrange themselves in the water-filled environment of the cytoplasm is to wrap the hydrophobic strands against each other sandwiched between the hydrophilic amino acids.

The packing in a coiled-coil interface is exceptionally tight, with almost complete van der Waals contact between the side-chains of the a and d residues.

Their primary feature is to facilitate protein-protein interaction and keep proteins or domains interlocked.

Viral entry into CD4-positive cells commences when three subunits of a glycoprotein 120 (gp120) bind to CD4 receptor and a coreceptor.

A spring-loaded mechanism is responsible for bringing the viral and cell membranes in close enough proximity that they will fuse.

The origin of the spring-loaded mechanism lies within the exposed gp41, which contains two consecutive heptad repeats (HR1 and HR2) following the fusion peptide at the N terminus of the protein.

[20] Finally, there are several proteins with coiled-coil domains involved in the kinetochore, which keeps chromosomes separated during cell division.

[28][29] Harbury et al. performed a landmark study using an archetypal coiled coil, GCN4, in which rules that govern the way that peptide sequence affects the oligomeric state (that is, the number of alpha-helices in the final assembly) were established.

This effect is due to a self-complementary hydrogen bonding between these residues, which would go unsatisfied if an N were paired with, for instance, an L on the opposing helix.

[33] Coiled-coil motifs have been experimented on as possible building block for nanostructures, in part because of their simple design and wide range of function based primarily on facilitating protein-protein interaction.

Coiled-coil domains can be made to bind to specific proteins or cell surface markers, allowing for more precise targeting in drug delivery.

[35] Other functions would be to help store and transport drugs within the body that would otherwise degrade rapidly, by creating nanotubes and other structure svia the interlocking of coiled-coil motifs.

[34] By utilizing the function of oligomerization of proteins via coiled-coil domains, antigen display can be amplified in vaccines, increasing their effectiveness.

[37] Using peptides with coiled-coil motifs for scaffolding has made it easier to create 3D structures for cell culturing.

Figure 1: The classic example of a coiled coil is the GCN4 leucine zipper (PDB accession code 1zik), which is a parallel, left-handed homodimer . However, many other types of coiled coil exist.
Side view of the gp41 hexamer that initiates the entry of HIV into its target cell.
Secondary and tertiary structure of the coiled-coil motif. The heptad repeat often consists of specific amino acids, seen in the figure. Knobs into packing is also shown. [ 27 ]
Some examples of protein nanostructures made using coiled-coil motifs. The top three pictures shown in the figure more accurately models the nanostructure, while the pictures underneath describe their basic shape. These may be used as building blocks to create further nanostructures. [ 27 ]