To clarify a bit, the protein is not cyclic, it is two of the wild type
protein molecules joined together by a short peptide linker creating a
"new" protein.
Here is my attempt at an ascii sketch,
2-fold 2-fold
__
( ) ( ) Linker
( ) ( )
( ) ( )
( ) ( )
( ) ( )
Linker (__) ( )
When looking at the crystal imagine half the unit cells of the crystal
have the linker on the "bottom" of the protein and the other half have it
on the top. The modified protein crystallizes in the same space group and
unit cell as the wild type.
I am just not sure how to describe it or for that matter refine the
system. One half of the new molecule is in the ASU while the other half
is related by the crystallographic two fold.
We have run the usual checks for twining and making sure we are in the
proper space group. We would not have this problem if we ignored the
higher symmetry, of course it would be wrong. It refines nicely in both
the space groups but the overall processing statistics really indicate
that it is in the higher space group.
Cheers,
Len
Leonard M. Thomas Ph.D.
Director, Macromolecular Crystallography Laboratory
Howard Hughes Medical Institute
California Institute of Technology
Division of Biology
1200 E. California Blvd. MC 114-96
Pasadena, CA 91125
626-395-2453
[EMAIL PROTECTED]
http://www.br.caltech.edu/cmclab
