Recombinant and purified proteins
Research proteins are molecules produced recombinantly, with or without a tag, or isolated and purified from a native source, supplied as reagents for functional assays, cell culture, interaction studies, assay development and chromatographic analysis: cytokines, chemokines, growth factors, enzymes, soluble receptors and plasma proteins. The application areas are cell biology and biochemistry. In the CABRU catalogue 10,312 references carry a protein name, 9,906 of them declared recombinant: 7,308 from FineTest, 1,633 from ReliaTech (cytokines and growth factors), 1,017 from Cayman Chemical, 186 from G Biosciences and 106 from BioVendor. Alongside them sit the 110 references from Enzyme Research Laboratories, devoted to coagulation proteins and enzymes, and the BSA from Solabia in 100 g, 500 g and 1 kg pack sizes.
The expression system changes the molecule
Two references sharing a name are not the same protein when they come from different systems. The system decides glycosylation, disulfide bonds, folding and the contaminants present, and that in turn decides whether the protein will be active in the intended assay.
| Production system | What it implies | When it is preferred |
|---|---|---|
| E. coli | No glycosylation; refolding may be needed; endotoxin has to be kept under control | Non-glycosylated cytokines and domains, when high yield matters |
| Mammalian cells (HEK293, CHO) | Glycosylation and folding close to the native form | Complex proteins and cell-based functional assays |
| Insect cells (baculovirus) | Intermediate post-translational modifications | Multidomain proteins, kinases, receptors |
| Purification from a native source | The isoforms and modifications actually present in the source | Coagulation enzymes and plasma proteins |
Tags, carrier and supply form
An affinity tag — His, GST, Fc — simplifies purification but stays on the molecule: in an interaction study or an activity test it has to be checked for interference, and an Fc tag dimerises the protein, changing its avidity. The carrier is the other fork: BSA-containing formulations stabilise the protein at low concentration, but should be avoided when the protein is to be labelled, conjugated or used where albumin interferes; carrier-free versions exist for those cases, and are less stable once diluted. Lyophilised proteins are reconstituted in the buffer stated by the manufacturer, aliquoted immediately, and not put through repeated freeze-thaw cycles. Recurring pack sizes are multiple — 50 µg/200 µg/1 mg on 6,261 references, 10 µg/50 µg/500 µg/1 mg on 1,024 — beside single sizes of 100 µg (401 references) and 5 µg (348).
What to compare before ordering
Species and isoform, expression system, presence and type of tag, carrier or carrier-free, declared purity and endotoxin level, pack size: these six fields make two apparently identical references comparable. For the coagulation area the use context is described on the Haemostasis and coagulation page. The full list is available in the product catalogue, filtering by company; if the protein sought is not there, CABRU checks availability among the manufacturers it represents.