PRODUCT REFERENCES
| Product name | Reference | Description | |
|---|---|---|---|
Fluorescent Streptavidin Dextrans-25T | PE Fluorescent Streptavidin Dextrans | RUO | 25 test | GO TO SHOP | |
Fluorescent Streptavidin Dextrans-100T | PE Fluorescent Streptavidin Dextrans | RUO | 100 test | GO TO SHOP |
Dextrans, polysaccharides extracted naturally from bacteria, are used in medicine for numerous applications as carriers for drugs or vaccines, but can also be used to incorporate other molecules of interest.
Such is the case of fluorescent dextrans, where fluorochromes, whether synthetic (FITC) or protein (PE or APC), and streptavidin, a protein with a high affinity for biotin and with four available binding sites, are coupled.
This dextran-fluorochrome-streptavidin complex (Fig. 1A) allows any biotinylated molecule to be bound via the biotin-streptavidin system (Fig. 1B).
This incorporated molecule, antigen, can be used to bind the whole complex to a target cell, or other established system, (Fig. 1C) and be detected by flow cytometry by means of the fluorochrome (Fig. 1D).
Figure 1: Dextran signalling system
Figure 2: Antigen-receptor binding comparing dextran conjugation with conventional conjugation.
A-B) We note the difference in spacing between the fluorochrome and the protein; the spacing in the dextran (A) is larger than in a conventional conjugation (B), which favours binding, as can be seen in the comparison of bindings C and F. The binding site in F is partially impeded by the spacing of the fluorochrome.
C-D) We compare the binding of a monobiotinylated protein (C) to a random normal biotinylated one (D). It is observed that random conjugation compromises the recognition of the protein, as the binding site may be conjugated to biotin and bind to streptavidin or the protein may become spatially unrecognisable. Monobiotinylation is targeted and the binding site is secured.
Cell labelling
Figure 3: We compared the fluorescent dextran cell labelling system (A) with the conventional system (B and C).
A) We note that it is not necessary to add a large amount of dextran to correctly label the specific population, since it is an efficient binding. This means that we avoid adding too much reagent that causes non-specific labelling and, therefore, we will achieve an optimal separation.
B) With a low amount of reagent, we do not have sufficient separation because we have non-specific labelling, either by the protein or by the fluorochrome. This happens, above all, because the protein-fluorochrome conjugation is not efficient and we have molecules that are not functional, but do cause non-specific binding, which forces us to increase the titre in order to bind the specific cell.
C) If we increase the titre (or optimise it), we can achieve a better separation, but with the risk of increasing non-specific binding due to excess reagent. Separation is not as efficient as with dextran.