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RE: [ccp4bb]: smallest diffracting crystals?
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One thing to consider is following:
A small number of repeating units afffects
the sampling of the lattice (see convolution
of molecular envelope with delta lattice function).
In practice this is used in the Scherrer formula for
determining particle sizes via line broadening
in powder diffraction.
With a 100 A molecule, the 1000 unit per period
limit is reached at 10 um. With very large
molecules and at very small dimensions, additional line
broadening contributing to lower S/N and thus
resolution must occur.
There is probably a specific optimum between
competing effects like minimum strain (mosaicity),
low absorption, line broadening and signal loss
for each crystal. I wager that 1 um is not going to
give hi res with large molecules/cells...
The S/N issue is, btw, often ignored in the single
molecule scattering presentations..
best regards, br
> -----Original Message-----
> From: email@example.com [mailto:firstname.lastname@example.org] On
> Behalf Of Anastassis Perrakis
> Sent: Wednesday, January 22, 2003 11:47 AM
> To: Richard Gillilan
> Cc: email@example.com
> Subject: Re: [ccp4bb]: smallest diffracting crystals?
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> *** CCP4 home page http://www.ccp4.ac.uk ***
> > I am interested to know:
> > What size is the smallest dimension protein crystal for which you
> > have obtained usable diffraction data on any synchrotron beamline.
> > I will be happy to summarize in the form of a histogram
> > if I get enough response.
> from the microfocus (ID13) experience between 1998-2000:
> ±3.2 A from ±5 micron thick plates (? not 100% sure of size )
> from Rod
> Mackinon's pumps ... - fairly anisotropic -
> a few datasets collected, some of which are used in Rod's nature
> paper(s).. not sure which one(s) .. he gets too many ;-))
> ±3.5 A from ±1 micron thick plates for Werner Kuehlbrant's
> - VERY anisotropic, I don't know what
> happened to these data
> 3.2 A from one ±30x5x2 micron xtal from O. Weichenrieder's/S.Cusack's
> Alu RNP isotropic (c221, complete data collected, 60Kd in AU)
> A funny cubic thingy from Stefania diMarco. M. Walsh et al, was
> 30x30x30 xtals and diffracted at 3.0 but it was 'nightmare in space
> group street'
> Belgian group for an iron containing protein got data on needles of
> 5-10 micron thickness 9veeeery long ones) up to 1.4 A !!!
> The Dortmund group had several pretty small xtals of GTPases
> that gave
> usuable data ... I am sure (?) Renaud and Klaus can
> enlighten us on the details of these
> 30x10x10 crystals (hey, these were mine !) were measured at
> 2.0, never
> reproduced and I wish I knew what was inside
> (45 kD protein- 22mer DNA complex but not both would fit - or the
> structure would be really weird .. structure pending)
> OF COURSE
> I am carefully avoiding all the things of similar size or bigger that
> never diffracted beyond 15-20 A !!!
> but the question was 'what WORKED ?' ;-))
> .... maybe I forget a few other small xtals but these are the
> ones that
> surfaced up in my memory now ...