Cystine knot

PDB 1hcn EBI

Cystine Knot

A cystine knot is a structural motif found in certain proteins characterized by the presence of three disulfide bonds that form a knotted configuration. This unique arrangement confers exceptional stability and rigidity to the protein structure, making cystine knot-containing proteins highly resistant to degradation and denaturation.

Structure

The cystine knot motif consists of six cysteine residues forming three disulfide bonds in a specific arrangement that results in a knot-like structure. The disulfide bonds are typically arranged in a pattern where one disulfide bond penetrates through a ring formed by the other two disulfide bonds, creating a stable and compact structure.

Function

Proteins containing cystine knots are known for their diverse biological functions, including roles in cell signaling, enzyme inhibition, and structural support. The unique stability provided by the cystine knot structure allows these proteins to withstand harsh conditions and maintain their functional integrity.

Examples

One of the most well-known examples of a protein containing a cystine knot motif is transforming growth factor beta (TGF-β), a cytokine involved in various cellular processes such as cell growth, differentiation, and immune response regulation. TGF-β utilizes the cystine knot structure to maintain its bioactivity and interact with specific cell surface receptors. Another example of a cystine knot-containing protein is nerve growth factor (NGF), which plays a crucial role in the development and survival of nerve cells. The cystine knot motif in NGF contributes to its stability and ability to bind to its receptor, facilitating neuronal growth and differentiation.

Applications

Due to their stability and unique structural properties, cystine knot-containing proteins have attracted significant interest in biotechnology and drug development. Researchers have explored the use of cystine knot scaffolds for designing novel therapeutics, such as peptide-based drugs and antibody mimetics, with enhanced stability and target specificity.

See also

• Disulfide bond
• Protein structure
• Biotechnology