In different organisms, the mode of interaction between two signaling proteins is not necessarily conserved
Park, S.Y., Beel, B.D., Simon, M.I., Bilwes, A.M., Crane, B.R.(2004) Proc.Natl.Acad.Sci.USA 101: 11646-11651
- PubMed: 15289606 
- DOI: 10.1073/pnas.0401038101
- PubMed Abstract: 
Although interfaces mediating protein-protein interactions are thought to be under strong evolutionary constraints, binding of the chemotaxis histidine kinase CheA to its phosphorylation target CheY suggests otherwise. The structure of Thermotoga mar ...