20 μM biotinylated peptide encompassing either the conserved CBD within human influenza M2 (Bio-β-Ala-LDRLFFKCIYRFFKHGL-amid) or a mutant where the CBD core motif is exchanged by alanine residues (Bio-β-Ala-LDRLAFKCIYRFAKHGL-amid) were inoculated with 50 μl NIH3T3 cell lysate (2 ml, T75 flask) for 90 min. Complexes were immobilized using 10 μl streptavidin coated paramagnetic microbeads and μ column (Miltenyi). Washed samples were eluted with 1× sample buffer preheated at 95°C for 2 min and 15 μl out of 70 μl eluate were separated by SDS PAGE, blotted to PVDF membrane and probed with rabbit anti-caveolin-1 antibody.