Isn't calcium-calmodulin one of the archetypical examples of the
crystal structure probably not representing the solution structure
(perhaps because the crystallization pH = 4.5)? Look at that linker
helix--how stable can that be in solution? I don't think a single one
of the NMR ca-calmodulin structures/conformers has the central helix
like that.
Jacob
On Fri, Feb 10, 2012 at 3:31 PM, Nat Echols <[log in to unmask]> wrote:
> Just to clarify - I actually think the original assumption that Jacob
> posted is generally reasonable. But it needn't necessarily follow
> that the conformation we see in crystal structures is always
> representative of the solution state; given the extreme range of
> conditions in which crystals grow, I would be surprised if there
> weren't counter-examples. I'm not familiar enough with the literature
> on domain swapping (e.g. diptheria toxin) to know if any of those
> structures are crystal packing artifacts.
>
> On Fri, Feb 10, 2012 at 1:04 PM, George <[log in to unmask]> wrote:
>>>Packing billions of copies into a compact lattice
>> Not so compact there is 40-80% water
>>>freezing it to 100K
>> We have frozen many times protein solutions in liquid nitrogen and then thaw
>> and were working OK
>>> non-physiological amounts of salt and various organics
>> What is the amount of salt and osmotic pressure in the cell??
>>>non-physiological pH too
>> What is the non-physiological pH too? I am sure that some enzymes they are
>> not working in pH 7. Also most of the proteins they have crystallized in pH
>> close to 7 so I would not say non-physiological.
>>
>> George
>>
>> PS There are lots of solution NMR structures as well supporting the
>> physiological crystal structures
>>
>>
>> -----Original Message-----
>> From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Nat
>> Echols
>> Sent: Friday, February 10, 2012 10:35 PM
>> To: [log in to unmask]
>> Subject: Re: [ccp4bb] Crystal Structures as Snapshots
>>
>> On Fri, Feb 10, 2012 at 12:29 PM, James Stroud <[log in to unmask]> wrote:
>>> How could they not be snapshots of conformations adopted in solution?
>>
>> Packing billions of copies of an irregularly-shaped protein into a
>> compact lattice and freezing it to 100K isn't necessarily
>> representative of "solution", especially when your solution contains
>> non-physiological amounts of salt and various organics (and possibly
>> non-physiological pH too).
>>
>> -Nat
>>
--
*******************************************
Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
email: [log in to unmask]
*******************************************
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