Hi all,

I'm working on a protein that I believe is tetrameric based on AUC, gel filtration, and crystallography. However, although my asymmetric unit has 4 chains, I cannot form the tetramer within the asymmetric unit. Instead, the asymmetric unit has two half-tetramers ('dimers'), and each full tetramer is completed by pairing up with another half-tetramer from a symmetry mate. If I load this structure into PISA, it recognizes that each of the 'dimers' forms a stable assembly, but cannot seem to assemble the tetramer. However, if I the generate symmetry mates in pymol to create a new PDB for the biological tetramer and give this to PISA, it recognizes a stable tetramer.

Specifically, chains A and C in the original PDB pair with chains A and C of the second symmetry mate generated in pymol, while chains B and D in the original pair with chains B and D of the third symmetry mate. How do I use this knowledge to generate a 3x4 rotation with translation matrix for PDB deposition?

Thanks,
Erik Klontz

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