I have to ship a batch of purified proteins at ambient temperature to a collaborator. The functional state, activity, and folding of the proteins after shipping are not important as they will be used for proteomics analysis. The proteins have been His-tag purified and precipitated with the methanol-chloroform-water method. I am wondering whether it would be better to ship the proteins as precipitates or freeze-dry the precipitate before shipment. Maybe the protein will be less stable as a precipitate compared to as freeze-dried during shipment, thus causing degradation and loss of material. On the other hand, re-solubilisation of freeze-dried proteins could be challenging, which might also lead to loss of material from incomplete re-solubilisation.
I know that each protein could behave differently but I would very much appreciate any comments on whether in general shipment as precipitate or as freeze-dried at ambient temperature could be better, i.e. lower degradation and loss of material?
Thanks a lot in advance!
In the line of what Dimitrios suggest I would put it the proteins in the buffer used for trypsin digestion (using a dessalting column) and then freeze-dried the solutions. I do no expect problems of redisolution with water (perhaps you may test this beforehand). And if freezedried I would not suffer if the sending is done at room temperature (i.e. if ice pack-sending is not possible).
Thanks for your answers Dimitrios and Rafael!
We usually air-dry the MCW precipitate, so all the methanol and chloroform should be gone, and then reconstitute the precipitate in 0.1% Rapigest. I use FASP-digestion, so the buffer of the protein stock will be exchanged for urea anyway. I am thus wondering if freeze-drying the protein in Rapigest would be beneficial. Couldn't I just freeze the MCW precipitate on dry ice and freeze-dry that?
I am just a bit skeptical of freeze-drying cause I once failed to re-solubilise a batch of freeze-dried proteins properly, which resulted in data not acceptable for publishing. Maybe I just got unlucky with that batch and re-solubilisation of freeze-dried proteins is not actually a huge problem?
Thanks for the reply Dimitrios!
I am specifically using a surfactant to facilitate solubilisation and denaturation of the protein. Rapigest is not a problem for digestion and it can be easily removed before MS analysis.
Unfortunately, my shipment takes ~5 days, so I am not sure the solution would stay frozen. Otherwise, I would surely opt for that.
I would recommend Freeze Drying, as a precipitate the protein may be even more susceptible to breakdown from other possible contamination. In freeze drying you will probably not see any significant degradation at all.
I have had mixed results reconstituting freeze dried proteins from vendors, and consider it something of an art. Protein left in an "elegant cake" has a lot of surface area and takes to rehydration well, while protein that is packed into a dense film doesn't solubilize well. The company (Hypermol) that provides us with readily soluble protein mentioned to me using unnamed (read: proprietary formulation) sugar in their formulation, and I have worked with protein formulated with trehalose (and surfactants and whatnot) in the past that has performed well under lyophilization/reconstitution.
I know that doesn't take you all the way to a solution to your problem, but hopefully it gets you a step in the right direction. Good luck!
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