Guangyu,
If I'm understanding your question correctly; you're asking if all other
things are equal (resolution, degree of disorder, etc), does improving
the data/parameter ratio result in an improved model?
The short answer is: (at least sometimes) yes.
Pete
Guangyu Zhu wrote:
> Ian,
>
> Because it is same protein, the high thermal motion is likely caused by crystal packing, and should be corrected by TLS refinement. The B left over should be similar.
>
> Anyway, this is just a hypothetical question. I tried to make other things same and just compare resolution and d/p. But you can still find difference. So if 80% crystal diffract to 3.0A too, then d/p ratio is much higher than 3.0A 50% crystal, it must be a more accurate refinement. What if 80% crystal diffract to 3.1, 3.2A, or 3.3A? Or I change the question to: could d/p ratio compensate some resolution?
>
> Thanks!
> Guangyu
>
> From: Ian Tickle <[log in to unmask]<mailto:[log in to unmask]>>
> Date: Friday, March 15, 2013 6:33 AM
> To: System Administrator <[log in to unmask]<mailto:[log in to unmask]>>
> Cc: "[log in to unmask]<mailto:[log in to unmask]>" <[log in to unmask]<mailto:[log in to unmask]>>
> Subject: Re: [ccp4bb] Resolution and data/parameter ratio, which one is more important?
>
>
> Hi Guangyu,
>
> I think it's not as straightforward as comparing d/p ratios, that is only one of several factors that influences precision. Another important factor would be the overall level of thermal motion & disorder which will most likely be significantly higher in the 3.6A 80% case; after all that's probably the reason that it only diffracts to 3.6A!
>
> All things considered I would go for the 3A form.
>
> Cheers
>
> -- Ian
>
>
> On 15 March 2013 00:27, Guangyu Zhu <[log in to unmask]<mailto:[log in to unmask]>> wrote:
> I have this question. For exmaple, a protein could be crystallized in two crystal forms. Two crystal form have same space group, and 1 molecule/asymm. One crystal form diffracts to 3A with 50% solvent; and the other diffracts to 3.6A with 80% solvent. The cell volume of 3.6A crystal must be 5/2=2.5 times larger because of higher solvent content. If both data collecte to same completeness (say 100%), 3.6A data actually have higher data/parameter ratio, 5/2/(3.6/3)**3= 1.45 times to 3A data. For refinement, better data/parameter should give more accurate structure, ie. 3.6A data is better. But higher resolution should give a better resolved electron density map. So which crystal form really give a better (more reliable and accurate) protein structure?
>
>
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