> But we're still talking about crystals, right? The whole reason for
> trying to crystallise our proteins/DNA/RNA is because we ideally want
> a perfect arrangement of molecules. So taking as a starting hypotheses
> the conservative approach that if the data really looks like P21 it
> probably is P21 seems a good idea to me.
"if the data really looks like P21--" what are the criteria for that? For
example, I believe p1 can have good-as-perfect 90deg angles, no? And also
equal cell dimensions? So I don't think you will be able to tell from the
positions of the spots on the detector, necessarily. Also, would it not be
more rigorous to say "I can gain a lot by assuming these molecules are in
p21?" Look, nobody thinks that every molecule in the crystal is identical,
so that is truly a convenient assumption. The symmetry, I think, is a
similar assumption at a different level.
By the way, I have always wondered whether anybody has looked into the
degree of intermolecular differences possible given all of the parameters in
our crystallographic models. In other words, would a microscopic observer
look at the molecules in the crystal and see what looks like a crowd from a
NYC street, or something more like an army formation? How much variety is
there at the molecular lever, I wonder?
> True: but how do you judge that those differences are within or
> outside of experimental noise?
Agreed!
> What if by refining in P1 the parametrisation makes those side-chains
> different in the first place? A poorly defined Lys side-chain suddenly
> becomes two significantly different poorly defined side-chain?
I don't know--depends on last question I think.
Jacob
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Jacob Pearson Keller
Northwestern University
Medical Scientist Training Program
Dallos Laboratory
F. Searle 1-240
2240 Campus Drive
Evanston IL 60208
lab: 847.491.2438
cel: 773.608.9185
email: [log in to unmask]
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