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Published August 10, 2004 | Published
Journal Article Open

In different organisms, the mode of interaction between two signaling proteins is not necessarily conserved


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 maritima CheA domain P2 in complex with CheY reveals a different association than that observed or the same Escherichia coli proteins. Similar regions of CheY bind CheA P2 in the two systems, but the CheA P2 domains differ by an approximate to90degrees rotation. CheA binds CheY with identical affinity in T. maritima and E. coli at the vastly different temperatures where the respective organisms live. Distinct sets of P2 residues mediate CheY binding in the two complexes; conservation patterns of these residues in CheA and compensations in CheY delineate two families of prokaryotic chemotaxis systems. A protein complex that has the same components and general function in different organisms, but an altered structure, indicates unanticipated complexity in the evolution of protein-protein interactions and cautions against extrapolating structural data from homologs.

Additional Information

© 2004 by the National Academy of Sciences. Edited by Janet Thornton, European Bioinformatics Institute, Cambridge, United Kingdom, and approved June 24, 2004 (received for review February 13, 2004). This paper was submitted directly (Track II) to the PNAS office. We thank Cristian Gradinaru for assistance and the Cornell High Energy Synchrotron Source for data collection facilities. This work was supported by National Institutes of Health Grant GM066775 (to B.R.C.). Data deposition: The atomic coordinates have been deposited in the Protein Data Bank, www.pdb.org (PDB ID code 1U0S).

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