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Re: [ccp4bb] poll: cutoff for "high resolution"
 

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CCP4bb <-- 2008 <-- May 2008 <-- 16 May 2008
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Subject: Position in Protein Expression
From: Steve Almo almo {- at -} MEDUSA {- dot -} BIOC {- dot -} AECOM {- dot -} YU {- dot -} EDU
Date: 2008-05-15 		Next message:
Subject: Re: problem of crystallization
From: Jens-Christian Navarro Poulsen jnp {- at -} KEMI {- dot -} KU {- dot -} DK
Date: 2008-05-16


Subject: Re: poll: cutoff for "high resolution"
From: Graeme Winter graeme {- dot -} winter {- at -} GOOGLEMAIL {- dot -} COM
Date: 2008-05-16
Hi All,

A problem with this is what do we mean by 1.2A data? I/sigma = 2 etc?
(not intended to restart the old resolution cutoff discussion)

From a personal point of view, I like to consider what features I can
see in the experimental electron density - so relatively high
resolution is when I can see the hole (in coot, default I/sig limits)
in Phe / Tyr. When I can see both holes in Trp I tend to think of it
as really quite high resolution, and when you can tell the difference
between C and O in the map from the size of the blobs, well to me that
is properly atomic ;o)

This probably correlates with the 1.2A rule, anyway. Low resolution
data would be, to me, when you can see the main chain but not see the
side chains so well.

However, this is from somebody who has spent a lot of time looking at
structural genomics data, so if you are into membrane proteins etc.
your perspective will most likely be different.

In passing, it is interesting to take a historical perspective on this
and look at some old papers - for example one on phase determination
for Myoglobin at a resolution of 2A (Dickerson, Kendrew & Strandberg,
1961, Acta Cryst 14, 1188) where the problem of the number of
reflections to consider required a change in approach for the phasing,
using a "digital solution" - there were some 9000 or so reflections as
opposed to 400 for the 6A structure... Looking at the same problem
today, with SAD data to 1.2A, would take several seconds with shelx.

Just my 1.5 p worth...

Cheers,

Graeme

2008/5/15 Bryan W. Lepore :
>
> On Thu, 15 May 2008, William Scott wrote:
>
> > On May 15, 2008, at 10:01 AM, Ed Pozharski wrote:
> >
> > > 1.2A (not surprisingly since this is about the length of covalent
> > > bond).
> > >
> >
> > A carbon-carbon single bond is about 1.55 Å.
> >
>
> the van der Waals radius of hydrogen is 1.2A (Eisenberg/Crothers, Pauling,
> 1960 ). this distance is referred to in "Sheldrick's 1.2A rule".
>
> http://scripts.iucr.org/cgi-bin/paper?ad0198
>
> -bryan
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