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Hi Lisa,

Speed is definitely a big factor here.  With a protein I work with I can get large crystals in myriad conditions that only diffract to about 4-5 Ang.  What I ended up doing was taking these crystals and seeding entire screens.  I found that not only would crystals appear sooner but it revealed novel crystallization conditions.  These seeded crystals would appear within minutes as Preben described and diffracted to better than 2 Ang.  Another thought would be to try limited proteolysis to see if you can identify a more stable construct.

-John

--

John Domsic
Postdoctoral Fellow
Gene Expression and Regulation Program
The Wistar Institute
Philadelphia, PA 19104


On Wed, Jan 16, 2013 at 7:17 AM, jens Preben Morth <[log in to unmask]> wrote:
Dear Lisa
It is not uncommon to see breakdown products when you run crystals on  gel. Espesially if they are older crystals, sometimes you even see higher molecular bands, these are probably due to intra molecular cross links formed over time.
If you are worried about stability, try to increase the crystallization speed, we have one example where we see a clear difference in both crystal quality and even space group depending on when we fish the crystals. The crystals appear within 5 min,  the best quality data sets come from crystals  we fish after only 30-60 min.
You may also have a little protease contamination of course, to prevent this add protease inhibitor, or DTT, or EDTA to you protein before you set it up.
cheers Preben


On 1/16/13 12:14 PM, LISA wrote:
Hi All,
I have an 36KD protein which can be crystallize in two days. Most of the crystals are very big. But all cystals have poor resolution,lower than 3.8 A. I picked some crystals, washed them in the mother solution and then run SDS-PAGE. It is surprised to find that different cystals have different components. Some crystals have several samll bands below the band of the protein. And in some crysals the bigger size band (as the construct should be) almost disappared and have smear. Does the protein was degradated in the crystals? Did someone met the similar problem as I? Thanks

All the best
lisa

--
J. Preben Morth, Ph.D
Group Leader
Membrane Transport Group
Nordic EMBL Partnership
Centre for Molecular Medicine Norway (NCMM)
University of Oslo
P.O.Box 1137 Blindern
0318 Oslo, Norway

Email: [log in to unmask]
Tel: +47 2284 0794

http://www.jpmorth.dk