Streptavidin

Streptavidin is a protein originally isolated from the bacterium Streptomyces avidinii. It is known for its extraordinarily high affinity for biotin (vitamin B7 or vitamin H), forming one of the strongest non-covalent interactions in nature . This unique property has made streptavidin a valuable tool in various biotechnological applications, including molecular biology, diagnostics, and nanotechnology.

Streptavidin is a tetrameric protein, meaning it consists of four identical subunits. Each subunit can bind one biotin molecule, resulting in a total of four biotin-binding sites per streptavidin molecule . The binding pocket of streptavidin is highly complementary to biotin, both in shape and through an extensive network of hydrogen bonds . This high affinity and specificity make streptavidin-biotin interactions extremely robust, resistant to extreme conditions such as high temperatures, pH variations, and the presence of denaturants .

Recombinant streptavidin refers to streptavidin that is produced using recombinant DNA technology. This involves cloning the streptavidin gene into a suitable expression system, such as Escherichia coli (E. coli), and then purifying the expressed protein . Recombinant production allows for large-scale manufacturing and the possibility of engineering streptavidin variants with desired properties, such as increased stability or altered biotin-binding characteristics .

The preparation of recombinant streptavidin typically involves several steps:

1. Cloning and Expression: The streptavidin gene is cloned into an expression vector and introduced into a host organism, commonly E. coli. The host cells are then cultured to produce the streptavidin protein .
2. Purification: The expressed streptavidin is purified using techniques such as affinity chromatography, which exploits its strong binding to biotin .
3. Refolding: If the protein is expressed as inclusion bodies (insoluble aggregates), it must be solubilized and refolded to regain its functional conformation .

Streptavidin’s primary chemical interaction is its binding to biotin. This interaction is utilized in various applications, such as:

• Detection and Labeling: Biotinylated molecules can be detected using streptavidin conjugated to enzymes or fluorescent labels .
• Purification: Biotinylated proteins or nucleic acids can be purified using streptavidin-coated beads .
• Crosslinking and Immobilization: Streptavidin can be used to immobilize biotinylated molecules on surfaces for various assays and experiments .

The streptavidin-biotin system is widely used in:

• Molecular Biology: For example, in Western blotting, ELISA, and immunohistochemistry .
• Nanotechnology: Streptavidin is used to create nanoscale assemblies and devices .
• Diagnostics: It is employed in various diagnostic assays to detect biotinylated targets .