Affinity purification Streptavidin Resin and buffers

Streptavidin Resin is designed for the single step small and large scale affinity purification of proteins and antibodies with a biotin tag. Biotin, a 244 Da vitamin (Vitamin H) molecule, exhibits an extraordinary binding affinity for avidin (Ka=10¹⁵ M⁻¹) and streptavidin (Ka=10¹⁵ M⁻¹). Biotin and (strept)avidin interaction is rapid and once the bond is established it can survive up to 3M guanidinehydrochloride and extremes of pH. Biotin-avidin bonds can only be reversed by denaturing the avidin protein molecule with 8M guanidine-hydrochloride at pH 1,5 or by autoclaving. The biotinylated molecules are efficiently probed with avidin or streptavidin conjugated to reporter molecules, such as peroxidases or phosphatases.

• ~4% cross-linked agarose
• Ligand density: >1 mg/ml
• Binding capacity: >100 nmoles/ml resin
• 50% suspension in PBS with preservative

Avidin is a glycoprotein with approximately 10% of its total mass coming from carbohydrates. Avidin has a molecular weight of 67 kDa and contains four identical 128 amino acid subunits that each have a single biotin binding domain. Avidin is a basic protein with an isoelectric pH of 10 to 10,5 and is readily soluble in aqueous buffers containing a wide range of salt, pH, temperature and other laboratory agents. This wide range of tolerance makes avidin suitable for a wide variety of analytical applications.

Streptavidin is a tetrameric protein containing 4 biotin binding sites. Streptavidin in many respects is similar to avidin except that it has no carbohydrate and has a slightly lower molecular weight of about 60 kDa. The solubility of streptavidin (isoelectric pH 5) in aqueous buffer is much lower than avidin, but the binding of streptavidin to biotin is similar to that of avidin. The advantage of streptavidin is that the lack of carbohydrates significantly reduces the amount of non-specific binding.

Streptavidin Resin consists of streptavidin coupled to ~4% cross-linked agarose, via a 15 carbon spacer arm.