BiotinStreptavidinSysteme

The Biotin-Streptavidin System is a widely used tool in biochemistry and molecular biology that relies on the strong non-covalent interaction between biotin and streptavidin. Biotin is a small vitamin, and streptavidin is a tetrameric protein originally isolated from Streptomyces avidinii. The pair provides one of the strongest known non-covalent bindings used in laboratory work.

Each streptavidin tetramer contains four biotin-binding sites, allowing up to four biotin molecules to bind simultaneously. The interaction has an exceptionally high affinity, with a dissociation constant on the order of 10^-14 to 10^-15 M, making the bond effectively irreversible under standard laboratory conditions. The complex is remarkably stable across wide ranges of pH and salt concentrations and can tolerate elevated temperatures in many buffers.

Applications of the system are diverse. It is commonly used for affinity purification by capturing biotinylated targets on streptavidin-coated beads or columns. It also enables immobilization of biotinylated biomolecules on surfaces, facilitating detection methods such as ELISA, microarrays, and biosensors. The system supports pull-down assays, in vitro labeling, and various forms of assay development that require robust and specific attachment of molecules.

Variants and limitations exist. Monovalent streptavidin reduces cross-linking for some applications, while neutravidin and related forms offer lower nonspecific binding. A practical constraint is the presence of free biotin in samples, which can compete with biotinylated targets and block capture. In vivo use is limited by immunogenicity and the exceptional stability of the complex.

History and impact: the interaction arose from studies of avidin and streptavidin and has become a foundational tool in modern biotechnology.