Protein-protein interactions are required for most cellular functions, yet little is known about the relationship between protein-protein interaction affinity and biological activity. To investigate this issue, we engineered a series of mutants that incrementally reduced the affinity of the yeast Sho1p SH3 domain for its in vivo target, the MAP kinase kinase Pbs2p. We demonstrate a strong linear correlation between the binding energy of these mutants and quantitative in vivo outputs from the HOG high-osmolarity response pathway controlled by Sho1p. In addition, we find that reduction in binding affinity for the correct target within this pathway causes a proportional increase in misactivation of the related mating pheromone response pathway and that strong binding affinity alone does not guarantee efficient biological activity. Our experiments also indicate that a second binding surface on the Sho1p SH3 domain is required for its proper in vivo function.
Marles, J. A., Dahesh, S., Haynes, J., Andrews, B. J., & Davidson, A. R. (2004). Protein-protein interaction affinity plays a crucial role in controlling the Sho1p-mediated signal transduction pathway in yeast. Molecular Cell, 14(6), 813–823. https://doi.org/10.1016/j.molcel.2004.05.024