Alternative method to verbs down assay for protein-protein interactions?

I was wondering what other methods exist in addition to GSP-fusion/pull down assay and mass spec. to determine interaction of one protein next to the other. I won't be able to perform crystallography, so that is not an selection.

Is there anything else? The organism I am working with is Paramecium. I would really appreciate some help. Thanks

Answers:

Those are the one and only recommended methods.
GOOD LUCK.