Of course, 222 has not a 4 axis, otherwise it would be a 4-fold axis.
But that's the output of the program. P4 exp. model has a 4-fold axis
along the longest axis, while the P222 MODEL has a 4-fold axis along the
smallest, which doesn't make any sense. Can you imagine something build
up with 4 identical subunits and 222 symmtry, but without a 4-fold axis
at the molecular level (I mean at the envelop resolution level)?
Em 29-07-2010 12:32, Vellieux Frederic escreveu:
Hi,
To quote you: "even my P222 experimental envelop does have a 4-fold
axis" - this is not suprising, a particle with 222 symmetry does not
have 4-fold symmetry. There are 3 mutually perpendicular 2-fold axes
that intersect at the origin (of the "particle", of the molecule) [and
for the nomenclature, these axes are named the P Q and R axes].
Fred.
Fred wrote:
Thanks all of you who promptly replied my question.
I should have been more precise. I was referring to the symmetry of
the tetrameric particle (point symmetry) at the molecular level not
at the atomic level. This question has arisen because I have
collected some SAXS data of my protein in solution and I don't have a
molecular model to superpose to the experimental envelop. Others
experimental data, gel filtration and NAT-PAGE, suggest a tetrameric
particle. On the other side, P1, P2, P222 and P4 experimental
envelops are quite different. So, I am not sure which symmetry to
take. Considering the native state (no ligands at all), 4 identical
subunits and that the interface of oligomarization have to be
conserved, I would take P222 or P4. However, I can be able to imagine
such spacial arrangement without a 4-fold axis at the molecular
level. Indeed, even my P222 experimental envelop does have a 4-fold
axis.
I appreciate if you could add some more comments on this.
Thanks in advance,
Fred
