Hi All,
Many thanks for those who shared their inputs. And sorry for not giving
more information about how the crystal was tested in the first instance.
The posted diffraction was obtained using the local resource (new
installed x-ray generator and new CCD Saturn 944+).
The Crystal to detector distance was ³50² with 10 min. exposure. The crystal
was mounted directly into the Cryo stream.
From the response I got, I think the crystal is a mix of protein and salt
(it is bitty).
I should try plunging the crystal in Liq. N2 rather than direct mounting in
the cryo stream.
Further to what mentioned by Jose, I should say that I can see spots below
15 A resolution (not that clear in the posted picture).
Again, thanks for your inputs...I¹ll keep trying to move away form this
salty crystal.
Thanks,
Ibrahim
On 4/3/08 3:58 PM, "Ibrahim Moustafa" <[EMAIL PROTECTED]> wrote:
> Dear CCP4 users,
>
> I¹m trying to crystallize a a small protein, 200 aa. Screening showed one
> promising hits which was further optimized by additive screen.
> Finally a beautiful crystal was obtained from conditions: 30% PEG4000 + 0.2 M
> Ammonium sulfate + 10 mM LaCl3. I was optimistic that the crystal
> Is a protein not a salt as the salt conc. is low in the crystallization buffer
> and LaSO4 would be soluble if it is formed. However, testing the
> Crystal on the local source showed a weird diffraction pattern, see the
> attached picture. It is clear that the crystal has a salt, from the strong
> Spots in the diffraction, also depending on the rotation angle, some images
> showed a clear salt. On the other hand there are closer spots
> Suggesting the presence of proteins (may be fibrous). Washing few crystals and
> running a gel revealed the presence of the protein.
>
> My question is what could be the diffracting object that gave the attached
> pattern? Could it be a salt crystal with a non-ordered protein inside?!
> If it is the case, has any body went through the same experience and got
> success to optimize the condition to get real protein crystal?
> I¹d be appreciated if people want to share their experience and to see what do
> they think of the pattern in the attached pic.
>
> Thanks in advance for your shared thought.
>
> Best,
> Ibrahim
