Just try RIPA buffer on ice, if you boil your sample you are going to lose the interaction

RIPA buffer recipe for total protein extract is as follows:

25mM Tris (10 mM sodium phosphate may be used instead), pH 7–8

150 mM NaCl

0.1% SDS (optional)

0.5% sodium deoxycholate

1% Triton X-100 or NP-40

Protease inhibitors such as PMSF or cocktail protease inhibitors which are commercially available (use according to the manufacturer's guide)

Good luck!!

Yes the RIPA buffer is your best friend for co-immunoprecipitation. with this recipe i was able to detect interactions between many different proteins including ion channels, cargo and a ridiculous 330kDa intracellular protein:

RIPA buffer (20mM Tris-HCl, pH 7.4, 50mM NaCl, 2mM MgCl2, 1% [vol/vol] NP40, 0.5% [mass/vol] sodium deoxycholate, and 0.1% [mass/vol] sodium dodecyl sulfate).

Make sure you add protease and phosphotase inhibitors. You will also need benzonase to digest the nucleic acids (they are the jelly that we see sometimes in lysates, digesting is better than spinning down). The 2 mM MgCl2 is here as a cofactor for the benzonase. I strongly advice against the use of EDTA or EGTA since they are interfering with the protease and phosphatase inhibitors. 

If your starting material is cultures cells, the buffer will do the lysis by itself, you only need to homogenize with the pipette, it you are doing IP from tissues, you will need to sonicate your samples but be careful of nor heating them during the sonication

Good luck!

I wanna ask, as the RIPA buffer contains SDS and sodium deoxycholate, these contents won't destroy the interactions ? and the RIPA buffer is just for strong interactions or really suit for some other weak interactions checked by Co-IP ? look forward to be answered ! many thanks !