protein-protein interaction (very strong)

[nieto]

Dear friends,

By means of a His-tag I heve detectected a strong protein-protein 
interaction.
The complex is eluted from the Ni-colum at 100 mM imidazol.The 
interaction is resistant up to 2M KCl. Both proteins separate in SDS-PAGE 
without B-mercaproethanol or boiling. 

Any suggestions of what can be going on here? Any nondenaturing ways of 
disrupting the interaction?

Thank you all.

jo

nieto at porthos.bio.ub.es