Recombinant Protein from E. coli FAQs

1. What kind of bacterial protein expression system does OriGene use?

When OriGene expresses and purifies protein from E.coli, we primarily use BL21 cells. We do offer custom options of purifying from variations of the BL21 cell line.

2. What is the OriGene guarantee for purified proteins?

OriGene guarantees that the purified protein will show at least 80% purity by SDS-PAGE/Coomassie staining and will be fully soluble at a minimum concentration of 0.05 µg/µL.

3. Where can I find the concentration of the purified protein that I received?

The concentration of the purified protein is determined by BCA assay (Pierce) and is on the tube and the Certificate of Analysis. In conjunction with the lot number from the tube, the concentration can serve as an indicator for this specific purification.

4. The standard size offered for the protein I am interested in is not enough for my assays. Can I order a larger amount?

On OriGene’s webpage for each bacterial expressed protein there is an option Bulk/Customize. Just click this button to begin the process of generating a custom quote for your desired quantity of protein.

5. What is the stability of OriGene’s purified protein?

OriGene guarantees that the protein will remain stable for up to three months after receipt pending appropriate storage and handling.

6. What are the recommended storage and handling conditions for protein samples?

Store at –80°C. Thaw on ice, aliquot to individual single-use tubes, and then re-freeze immediately. Only 2-3 freeze thaw cycles are recommended.

7. Does OriGene guarantee the function of the purified protein in all assays?

OriGene cannot guarantee that all proteins will retain all putative functions due to the large number of variables involved, e.g. essential co-factors may not be co-purified. OriGene has taken several steps to preserve maximum functionality. These steps include:

• Only small epitope tags were fused to the protein.
• All proteins are fully soluble in the final buffer.

8. Is a stabilizing agent added to the purified protein?

The final buffer for all proteins contains 10% glycerol as a stabilizing agent.

9. What buffer is the protein provided in?

Please refer to our webpage for the specific E.coli expressed protein you are interested in to find the buffer details for each product. On the product’s page, this information can be found in Product Data under “Buffer”.

10. What method does OriGene use to purify the proteins?

E.coli proteins are primarily purified with a His6-tag using Ni-affinity chromatography unless specified otherwise within a protein’s Product Data. Please inquire with our Custom Protein service if you are interested in tag removal or would like a different tag.

11. Will the His6 tag affect the function of protein?

OriGene cannot guarantee that the epitope tags will not affect the protein’s functions but we have specifically selected the His6 epitope because it is very small, and less likely to cause interference.

12. OriGene has informed me that my protein cannot be purified by their standard method. What are my options?

If OriGene fails to purify a protein using our standard method, we do not charge any fee and you can simply cancel the order. If the protein is essential but purity is less of an issue, we can often supply a whole cell lysate or a partially purified preparation of the overexpressed protein at a discount. Please contact our technical support team at techsupport@origene.com for information on this option. Although we cannot provide this purified protein using our standard approach, we might be able to supply it as a custom purification. For information on this service, please contact proteincustom@origene.com.

13. What do I do if I can't find my protein of interest?

OriGene is routinely adding new proteins on a quarterly basis. Please check our website frequently or fill out our Custom Service form. OriGene will contact you to discuss your needs in detail.

14. What source do you use for the predicted molecular weight of the antigen?

We mainly use the swissprot webpage to help predict the molecular weight of unprocessed protein. Please refer to https://www.expasy.org/resources/uniprotkb-swiss-prot.

15. If the Coomassie gel shows a protein of a molecular weight different from the predicted molecular weight, does this mean I received the wrong protein?

The predicted molecular weight is calculated from the protein primary amino acid composition. There could be some discrepancy from the actual molecular weight, if there were post-translational modifications or known proteolytic activity. In this case, OriGene strongly suggests researchers check related literature on this particular protein.

16. How should I cite your product?

Here is our guideline:
Full Product Name, OriGene Technologies Inc., Rockville, MD, USA, Catalog #, Lot #.
In addition, we would love to hear from you when the paper is published. Email us a copy of the accepted manuscript and receive a special gift.

17. How do I prepare recombinant proteins for cell culture purpose?

We recommend all proteins be diluted into cell culture medium at required concentrations, and go through a 0.2 µm sterile filtration step before being applied to cell culture. Most E.coli proteins are not guaranteed to be endotoxin free which could impact cell culture experiments. Please inquire with our Custom Protein Service to find out whether it’s possible to acquire your protein of interest endotoxin free, or consider our MVPro recombinant proteins, which are expressed in HEK293 cells.