Tandem affinity purification combined with mass spectrometry to identify components of protein complexes.

Most biological processes are governed by multiprotein complexes rather than individual proteins. Identification of protein complexes therefore is becoming increasingly important to gain a molecular understanding of cells and organisms. Mass spectrometry-based proteomics combined with affinity-tag-based protein purification is one of the most effective strategies to isolate and identify protein complexes. The development of tandem-affinity purification approaches has revolutionized proteomics experiments. These two-step affinity purification strategies allow rapid, effective purification of protein complexes and, at the same time, minimize background. Identification of even very low-abundant protein complexes with modern sensitive mass spectrometers has become routine. Here, we describe two general strategies for tandem-affinity purification followed by mass spectrometric identification of protein complexes.