The biotin-streptavidin bond is the strongest noncovalent biological interaction known, having a dissociation constant, Kd, in the order of 4x10
-14 M. The strength and specificity of the interaction has led it to be one of the most widely used affinity pairs in molecular, immunological, and cellular assays. In most assays, streptavidin is coupled to a solid phase, such as a magnetic bead, a microtiter plate, or a biosensor chip, while biotin is coupled to the moiety of interest, often a nucleic acid, protein, or antibody.
Dynabeads® Streptavidin are uniform, superparamagnetic beads with a streptavidin monolayer covalently coupled to the surface which ensures negligible streptavidin leakage and therefore batch consistency and reproducibility of results. These beads give simple and stable binding of biotinylated molecules such as small molecules, peptides, proteins, antibodies, sugars, lectins, oligonucleotides, DNA/RNA etc.
The Dynabeads® Streptavidin Trial Kit from Invitrogen includes four different kinds of superparamagnetic beads each with different characteristics. Dynabeads M-280 Streptavidin and Dynabeads MyOne™ Streptavidin T1 are commonly used for protein and nucleic acids applications. Dynabeads M-270 Streptavidin and Dynabeads MyOne Streptavidin C1 are preferred for nucleic acid diagnostics, specifically with samples with a high chaotropic salt concentration, immunoassays involving small biotinylated antigens and applications that are not compatible with BSA (these beads are not blocked with BSA). MyOne Dynabeads offer increased binding capacity and slower sedimentation rate, making them ideal for automated applications and for when larger amounts of biotinylated ligand, or their specific target, need to be isolated.
For me, the trial kit was a great offer to test different bead formulations for different applications and by doing so, to optimize the experimental set-up. I used the beads for the isolation of biotinylated RNA as well as biotinylated proteins isolated from human cells.
The handling of the beads is easy, but it requires additional material. A magnet for the washing as well as the isolation steps is necessary. I used the Dynal MCP-S magnet (Invitrogen), which is suitable for holding 1.5 ml tubes or even 500 ul PCR tubes (equaling the new DynaMagTM-2 magnet). Usually, the beads get immobilized first and are subsequently washed to remove any unwanted preservatives. For different applications, like RNA or protein binding, alternative washing and binding strategies are suggested in the protocol and are easy to follow. The incubation times for the binding of biotinylated molecules vary and needs to be tested empirically. The manufacturer’s protocol also includes paragraphs about the release of immobilized biotinylated molecules. In addition, weblinks are listed to get more information regarding immunoassay strategies and automation.
In summary, I found it very useful to get a variety of different beads to get used to the handling as well as to optimize the protocol for my experimental needs. The beads performed in a reproducible way with great consistency.
Research Assistant Professor
Department of Surgery, Division of Vascular Surgery
University of Utah