Everything about Coiled Coil totally explained
» For the coiled coil shape in general, see coil.
A
coiled coil is a
structural motif in
proteins, in which 2-7
alpha-helices are coiled together like the strands of a rope (
Dimers and
trimers are the most common types). Many coiled coil type proteins are involved in important biological functions such as the regulation of
gene expression for example
transcription factors. Notable examples are the proteins the
oncoproteins c-fos and jun, and the muscle protein
tropomyosin.
Molecular structure of coiled coils
Coiled coils usually contain a repeated seven
amino acid residue pattern called
heptad repeats. The interacting surface between the helices often contain
hydrophobic residues, such as
leucine arranged in a so called
leucine zipper. The most favorable way for such two 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. It is thus the burial of hydrophobic surfaces, that provides the
thermodynamic driving force for the dimerization.
The α-helices may be parallel or antiparallel, and usually adopt a
left-handed super-coil (Figure 1). Although disfavored, a few
right-handed coiled coils have also been observed in nature and in designed proteins.
Biological roles of coiled coils
Role of coiled coils in HIV infection
A key step in the
entry of
HIV into human cells is the exposure of a trimeric, parallel coiled coil known as
gp41. The gp41 trimer is normally covered by another surface glycoprotein known as
gp120, which protects it from antibodies. Upon binding to the target cell, gp120 undergoes a conformational change that exposes the gp41 trimer, whose hydrophobic N-terminal tails enter the target cell membrane. Three other helices of gp41 fold down into the grooves of the gp41 coiled coil trimer, forming a hexamer, and drawing the viral membrane and target-cell membrane close enough to fuse. The virus then enters the cell and begins its replication. Recently, inhibitors that bind in the gp41 grooves have been developed, such as
Fuzeon.
Coiled coils as dimerization tags
Because of their specific interaction coiled coils can be used as a dimerization "tag".
History of coiled coils
The possibility of coiled coils for α-
keratin was proposed by
Francis Crick in 1952 as well as mathematical methods for determining their structure.
Remarkably this was soon after the structure of the
alpha helix was suggested in 1951 by
Linus Pauling and coworkers
Further Information
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