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 <[EMAIL PROTECTED]>:
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
