I have read in one of the article that they have crystallized protein by screening the protein solution which was partially aggregated before even setting and the drop and finally they got good diffraction quality crystals.
Is it possible to screen conditions with aggregated protein protein (Partially) ?
I think this is very difficult. You may try some new constructs to stabilize your protein.
You have to get the soluble and stable version of this protein. Sometimes, due to oxidations of the proteins, proteins get insoluble. In this case you can try 2-marcaptoethanol. There are also many several ways you can try-
1. Point mutations
2. Truncations and deletions
3. Fuse your protein with other soluble protein like MBP or lysozyme.
Some proteins tend to precipitate immediately after metal affinity chromatography due to some leached metal ions (nickel or cobalt). You can add some EDTA in the elution tube and dialyze out the EDTA later. Check your Pi-pH relationship and see if additives are required to keep the protein stable in solution. Check different buffers as well. You should know why the protein is precipitating.
It is tough. Aggregation/precipitation and crystal formation are ways of establishing equilibrium (solubility). Additives are not always the only way. If you are precipitating, perhaps you need a lower starting protein concentration and control the path to supersaturation carefully.
Additives are the key. You need to find out the lowest level of salt and imidazole you can get without precipitation. Then try tiny amounts of Triton or mild detergents to compensate. Protein concentration is also critical. Not necessarily you need a 10 mg/ml protein concentration to set up your drops.
If you decide to go for mutations/truncations check Xtal-Pred
http://ffas.burnham.org/XtalPred-cgi/xtal.pl
Which will help you figure out the problematic regions.
SERp is also another nice algorithm that can help you find problematic regions or residues:
http://services.mbi.ucla.edu/SER/
best-
I do not believe, to obtain crystals of the protein must be homogeneous and not contain precipitates (unstructured proteins).
Its possible.
But the chances are one in 10,000
When you see the aggregation not all the protein may be aggregated. Some may not be aggregated. If the crystal packing requires low amount of protein at low concentration there are chances of getting crystals.
We have never tried this since we rely on the theoretical principles. The PI, lab mates and friends would always say do not waste time on this aggregation. But if there is excessive funding, manpower and consumables it worth to try this out.
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