[ccp4bb] SSM superposition of a heterodimer of related chains such that A->B and B->A

[Norbert Straeter]

Dear All,
                        
I have a heterodimer of two related subunits (A and B). Now I want to
superimpose it using a secondary structure matching (SSM) algorithm
(e.g. CCP4 superpose or the coot algorithm) such that the superposition
matches A onto B and B onto A at the same time. For a perfectly
symmetrical closed C2 dimer, it would not make a difference if I just
superimposed A onto B, but it is unsymmetrical. I know that this is easy
to specify in lsqkab when knowing the matching residue pairs. Does
anybody know an SSM program where I can specify the chains to be
superimposed (A->B and B->A)? 
                        
Thanks,
                        
Norbert