non-diffractable xtals!

[manian1 at vsnl.com]

Dear Bhupesh:

> 
> I have a xtal of a multimeric protein (final Mw of 80 kDa) which does
> does diffract.  I have tried various additives to the precipitant and
> have two-three xtal forms from those, av size 0.3 mm3/0.2mm3 app.  The
> xtals do not seem to grow larger (hanging drop vapor diffusion).  The
> xtals though look good but do not diffract beyond 10-12 A and even at
> this low resolution do not give a good diffraction pattern. (15 deg 
> and cryo temperatures).

>        How can I grow my xtals larger (if need be)?

Use the crystals that you have obtained as seeds. Also, increase the   
protein concentration if possible.

>     How do I make them diffractable?

Try crosslinking the protein either
a) in the crystals  or
b) before starting the crystallization.

>     Why don't they diffract at all? (apparently there are similar.. 
>     ...............................................................

      If the crosslinking makes the crystals  diffract better, then
      you have an explanation.

      Good luck

      E. Subramanian
      Dept. of Biophysics
      University of Madras, Chennai-600 025
      manian1 at vsnl.com