Indeed, but wouldn't consideration of micelle size affect our
estimation of the number of molecules in the asu, in some cases
significantly?
The crystal packing of some membrane proteins shows that they tend to
pack as "potatoes in space" with relatively few protein-protein
contacts and with detergent micelles presumably providing the rest of
the crystal packing interactions. That also explains the often
significant diffraction anisotropy observed in such crystals. One
classic example is the prototypical potassium channel structure (KCSA)
(PDB entry 1bl8).
Savvas
Quoting Edward Berry <[log in to unmask]>:
> I would use a very general definition for "solvent",
> including disordered detergent and lipids.
> As you know in many cases ordered detergents and lipids
> have been modeled in the coordinates, so they are part of
> the model not the solvent. In some cases I think waters
> should be included in the model not solvent- say for
> structural waters buried in the protein at least.
>
> Ed
>
> Savvas Savvides wrote:
>
>> Dear colleagues,
>>
>> in estimating the solvent content of membrane protein crystals it
>> would only seem reasonable that micelle size should also be taken
>> into account. Depending on the aggregation number and MW of a given
>> detergent, the concentation of detergent used, and the buffer
>> conditions, one may have micelles on the order of 15-25 kDa or even
>> 35-50 kDa for detergents with alkyl chains of more than 10 carbons.
>>
>> However, when I took a look in a handful of papers reporting
>> Matthews' numbers for membrane protein crystals, it became apparent
>> that only the protein MW is used in such estimates. I am
>> beginning to wonder if one should even bother reporting a
>> Matthews number for a membrane protein crystal given the
>> uncertainties surrounding size and role of micelles in crystal
>> packing.
>>
>> Any thoughts on this?
>>
>> best wishes
>> Savvas
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