Dear Klaus,
With extensive travel in the meantime, we're sorry that it took us so long to
get
back to you on this.
Well, the true answer is that any resolution might be expected on the PX
Scanner.
Thus, sometimes we have observed higher resolutions on the PX Scanner than
observed from the 'same' protein crystals using a third generation synchrotron
source.
The point is that as well as determining the 'native' diffraction qualities
(resolution limit,
mosaicity and unit cell, etc.) of the chosen crystal, using the PX Scanner one
can also
establish the efficacy of the cryo-protection and the further 'handling' stages
of the
crystal workflow, etc. (So, in the cases above, perhaps the cryo-conditions
were
'wrong', etc...).
Moreover, using the PX Scanner, one can unambiguously identify the
best-diffracting
individual crystal in any droplet across the whole crystallisation plate: most
importantly
in situ without any kind of 'disturbance'... And even if the crystals do indeed
diffract - on the PX Scanner, to lower resolution than they do on a more
powerful
source, of course you can still rank them and then pick up the clearly 'best'
ones for further
analysis. As experienced by many researchers: there can be very significant
differences
between crystals, even grown in the same drop.
You, all, are most welcome to visit our labs, bringing your plates, in order to
collect
in situ crystal diffraction data: as an evaluation both of your crystals and the
PX Scanner instrument. We look forward to this !
Yours,
Tadeusz Skarzynski
Marcus Winter
(Oxford Diffraction Ltd. - now Agilent Technologies)
-----Original Message-----
From: Klaus Fütterer [mailto:k.futte...@bham.ac.uk]
Sent: 30 September 2010 11:00
To: WINTER,MARCUS (A-Varian,ex1)
Cc: CCP4BB@JISCMAIL.AC.UK
Subject: Re: [ccp4bb] Lousy diffraction at home but fantastic at the
synchrotron?
Marcus,
May I ask the following: assuming 8 A is obtained from a single
crystal on the home source, what diffraction limit would one expect
on the PX scanner?
Best regards,
Klaus
=======================================================================
Klaus Fütterer, Ph.D.
Reader in Structural Biology
Undergraduate Admissions
School of Biosciences P: +44-(0)-121-414 5895
University of Birmingham F: +44-(0)-121-414 5925
Edgbaston E: k.futte...@bham.ac.uk
Birmingham, B15 2TT, UK W: www.biochemistry.bham.ac.uk/klaus/
=======================================================================
On 30 Sep 2010, at 10:44, Marcus Winter wrote:
>
>
> This recent discussion does tend towards the ideal scenario: of
> identifying ones
> best-diffracting crystals... before embarking on the synchrotron trip.
>
> The established Oxford Diffraction PX Scanner home laboratory
> instrument can
> therefore be most useful. This enables the direct X-ray screening
> of individual
> (putative) single crystal objects, in situ, in the (any SBS format)
> crystallisation plate.
>
>
> Yours sincerely,
>
> Marcus Winter (Oxford Diffraction Ltd. - now Agilent Technologies)
>
>
>
> -----Original Message-----
> From: CCP4 bulletin board [mailto:ccp...@jiscmail.ac.uk] On Behalf
> Of Phil Jeffrey
> Sent: 28 September 2010 19:20
> To: CCP4BB@JISCMAIL.AC.UK
> Subject: Re: [ccp4bb] Lousy diffraction at home but fantastic at
> the synchrotron?
>
> Often this reflect crystal size - a small crystal in a big beam (or
> one
> with a long path in air) on a home source would see the small
> diffraction signal drop below the noise level quite quickly - often at
> the low resolution intensity dip that sits very approximately around 6
> Angstrom. On a synchrotron source with a tight low-divergence beam
> that
> matches more closely the crystal dimensions that same crystal will
> appear to do rather better.
>
> Also one is more likely to expose the crystal longer (in terms of
> total
> photon numbers) at a synchrotron, which itself begets better signal/
> noise.
>
> Alternatively: everyone tries harder before synchrotron trips....
>
> Phil Jeffrey
> Princeton
>
> On 9/28/10 1:27 PM, Francis E Reyes wrote:
> > Hi all
> >
> > I'm interested in the scenario where crystals were screened at
> home and
> > gave lousy (say < 8-10A) but when illuminated with synchrotron
> radiation
> > gave reasonable diffraction ( > 3A) ? Why the discrepancy?
> >
> > Thanks
> >
> > F
