Data on protein complexes are collected from the study of individual systems, and more recently through high-throughput experiments, such as yeast two-hybrid (Y2H) [1,2] and tandem affinity purification followed by mass spectrometry (TAP/MS) [3,4]. The TAP/MS approach helps pinpoint proteins that interact with a tagged bait protein, either directly or indirectly, and are thus suited to identify multi-protein complexes. In fact, several research groups have systematically applied TAP/MS technology to study protein complexes involved in different signaling pathways [5].