The identification of protein binding partners often facilitates understanding of protein complex function. However, identifying binding partners has proven difficult because proteins are often bound to insoluble structures or are only present during certain stages of the cell cycle. Fortunately,Xenopuseggs stockpile many proteins, which are typically insoluble, as soluble subcomplexes to facilitate rapid early embryonic divisions. We exploited this by developing a purification scheme usingXenopusegg extracts to isolate Coomassie-stainable amounts of the xNdc80 kinetochore complex. In this schemeXenopuseggs are directly made into a mitotic high-speed supernatant and then flowed over three chromatographic columns: heparin, MONOQ, and Superose 6 gel filtration columns. A final immunoprecipitation is then performed from the peak Superose 6 column to yield Ndc80 complex purified to homogeneity. With minor modification and manipulation ofXenopusegg extracts, this protocol can easily be adapted for purification of other protein complexes.
