A constraint network of interactions: protein-protein interaction analysis of the yeast type II phosphatase Ptc1p and its adaptor protein Nbp2p.

We used a generally applicable strategy to collect and structure the protein interactions of the yeast type II protein phosphatase Ptc1p and its binding partner Nbp2p. The procedure transformed primary unstructured protein interaction data into an ensemble of alternative interaction states. Certain combinations of proteins are allowed in different network configurations. Nbp2p serves as the network hub and brings seven kinases in close contact to Ptc1p. As a consequence, the deletion of NBP2 affects several cellular processes including organelle inheritance and the responses to mating hormone, cell wall stress and high osmolarity; it also impairs the proper execution of the morphogenetic program. Our constraint interaction map provides a basis for understanding a subset of the observed phenotypes and assigns the Ptc1p-Nbp2p module a role in synchronizing the associated kinases during the cell cycle.