Coimmunopresipiering

Coimmunopresipiering, or co-immunoprecipitation (co-IP), is a biochemical method used to test whether two or more proteins interact physically within a cell or tissue. The technique centers on an antibody that specifically recognizes a target protein, called the bait. When a cell or tissue lysate is incubated with the antibody and captured on beads, proteins bound to the bait, the prey, are co-precipitated and enriched for analysis.

The basic workflow involves preparing a non-denaturing lysate to preserve protein interactions, incubating it with an antibody against the bait, and pulling down the antibody-protein complex with protein A/G beads. After washing to reduce non-specific binding, the precipitated material is eluted and analyzed, commonly by western blotting or mass spectrometry, to detect the presence of potential prey proteins.

Interpretation of results requires appropriate controls. A successful co-IP shows enrichment of a prey protein in the bait pull-down compared with controls, but it does not prove a direct physical interaction; the association may be indirect or mediated by other components in a complex. Essential controls include a non-specific IgG control, beads-only control, and reciprocal co-IP experiments where feasible.

Limitations and caveats include dependence on antibody quality and epitope accessibility, choice of detergent and lysis conditions, potential artifacts from overexpression, and loss of transient interactions during washing. To strengthen conclusions, researchers often combine co-IP with complementary approaches such as cross-linking, reciprocal co-IP, or alternative interaction assays. Variants include endogenous versus overexpressed systems and tandem affinity purification, depending on the research question.