Coiled coil

Coiled coil is a structural motif in proteins in which 2-7 alpha-helices are coiled together like the strands of a rope. This motif is characterized by a repeating pattern of hydrophobic and hydrophilic amino acids, which stabilizes the structure. Coiled coils play a crucial role in the structure and function of a wide range of proteins involved in various biological processes, including muscle contraction, cell division, and the response of cells to external signals.

Structure

The coiled coil structure is formed by the winding of two or more alpha-helices around each other, creating a supercoil. The helices in a coiled coil are typically in a left-handed supercoil, although right-handed supercoils do exist. The stability of the coiled coil structure is primarily due to hydrophobic interactions between side chains of amino acids that are positioned on one side of the helices. These hydrophobic residues are often leucine, isoleucine, or valine, leading to the term "leucine zipper" being used to describe some coiled coils. Additionally, electrostatic interactions and hydrogen bonds between the helices further stabilize the structure.

Function

Coiled coils are involved in a variety of cellular functions. They play a key role in the formation of fibrous proteins, such as keratin and collagen, which are essential for the structural integrity of cells and tissues. In muscle cells, coiled coils are part of the myosin and tropomyosin proteins, where they are crucial for muscle contraction. Coiled coils are also involved in the regulation of gene expression by facilitating the dimerization of transcription factors, and in the assembly of viral proteins during the formation of viral capsids.

Examples

Some well-known proteins that contain coiled coil domains include:

• Myosin, which plays a central role in muscle contraction and cell motility.
• Fos and Jun, transcription factors that dimerize through their coiled coil domains to form the AP-1 complex, which regulates gene expression.
• Tropomyosin, which regulates the access of myosin to actin filaments in muscle cells.
• Lamin, which provides structural support to the nuclear envelope.

Diseases Associated with Coiled Coils

Mutations in the genes encoding coiled coil proteins can lead to a variety of diseases. For example, mutations in keratin genes can cause skin disorders such as epidermolysis bullosa simplex, while mutations in lamin genes can lead to a group of diseases known as laminopathies, which include muscular dystrophies and premature aging syndromes.

Research and Applications

Understanding the structure and function of coiled coils has important implications for biotechnology and medicine. For instance, synthetic coiled coils are being explored as components of novel biomaterials and as tools for the targeted delivery of therapeutic agents. Additionally, the role of coiled coils in diseases makes them potential targets for therapeutic intervention.