immunoprecipitate

Immunoprecipitation is a laboratory method used to isolate a specific antigen from a complex mixture using an antibody that binds to that antigen. The resulting immunoprecipitate consists of the antigen bound to the antibody, typically captured on a solid support such as magnetic or agarose beads coated with protein A or protein G.

In a typical workflow, cells or tissues are lysed to release proteins. The lysate is incubated with an antibody specific to the target antigen, allowing binding. The antibody–antigen complexes are then captured by beads and collected by centrifugation or magnetic separation. After extensive washing to remove non-specific proteins, the target can be eluted from the beads by changing the pH or using competitive peptide, or by denaturation. The enriched material is commonly analyzed by Western blotting, mass spectrometry, or enzymatic assays.

Immunoprecipitation is widely used to study protein function and interactions. Co-immunoprecipitation (co-IP) enables identification of binding partners by pulling down protein complexes. Reverse IP and cross-linking strategies help stabilize interactions or map networks. IP can also enrich post-translationally modified forms using modification-specific antibodies.

Key considerations include antibody quality and specificity, choice of lysis conditions, and appropriate controls such as non-specific IgG and beads-only samples. Non-specific binding and epitope masking can lead to artifacts, so optimization and proper controls are essential.

Immunoprecipitation serves both analytical and preparative purposes, enabling focused study of proteins within complex mixtures and facilitating downstream analyses such as mass spectrometry or functional assays.