Re: [ccp4bb]: Xtals come out on the skin of drop surface

[Clemens Grimm <grimm@mailer.uni-marburg.de>]

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Dear all,

I am working on a RNA/protein cocrystallisation project and I am
experiencing the same skin/small crystal problem. As I have seen exactly
the same behaviour with other RNA/protein cocrystals, I would suspect
that this may be nucleic-acid specific. My observations are, that this
skin originates from some kind of phase separation or fine precipitate.
This PPT then sediments and forms the skin in which the crystals grow.
If I reduce the precipitant concentration I get clear drops and no skin
- but also no more crystals.


Clemens



========================================
Clemens Grimm
Institute for Pharmaceutical Chemistry
University of Marburg
Marbacher Weg 6
D-35032 Marburg, Germany
e-mail: grimm@mailer.uni-marburg.de
phone: +49(0)6421/28-25845
fax  : +49(0)6421/28-28994
========================================            




Serge COHEN wrote:
> 
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> 
> At 1:27 +0100 15/12/01, OnLineHelpForm wrote:
> >Dear all,
> >
> >Sorry for this non-CCP4 related questions but I sincerely hope you guys
> >can help me out.  Recently I got my protein /DNA complex crystallized
> >beautifully in PEG 1K or 3K.   However, these crystals are relatively
> >small and stop growing when they just come.   In other words, I can not
> >ever tell they are growing.    To my surprise, I found there is a thick
> >skin on the surface of  drops and all crystals come sticking to that skin.
> >It is said the skin forms out of  denatured protein.     So my question is
> >how I can possibly make my protein happy in drops and hopefully facilitate
> >their growing.     Any suggestions are highly appreciated.
> >
> >Thanks in advance,
> >
> >
> >Aidong Han, hana@colorado.edu
> 
> Hi;
> 
> I had some drops with skin, in my case the skin was oxydation dependant.
> i.e. if I had some anti oxydant (DTT, etc...) to th protein stock I no skin
> (or it takes more time to appear).
> 
> As well, you can still get the Xtal from out the skin, indeed using
> acupuncture needles, I first touch the skin at the root of the xtall to
> detach it from the skin, and then use the needli to remove the skin. I
> found it much easier to separate the xtal from the skin before breaking the
> skin.
> 
> Serge.
> 
> ------------------------------------------------------
> Serge Cohen.
> 
> PGP key id : 69B1D346
> ------------------------------------------------------