Determinants of homodimerization specificity in histidine kinases.

TitleDeterminants of homodimerization specificity in histidine kinases.
Publication TypeJournal Article
Year of Publication2011
AuthorsAshenberg O, Rozen-Gagnon K, Laub MT, Keating AE
JournalJournal of molecular biology
KeywordsAmino Acid Substitution, Bacterial Outer Membrane Proteins, Bacterial Outer Membrane Proteins: chemistry, Bacterial Outer Membrane Proteins: genetics, Bacterial Outer Membrane Proteins: metabolism, Escherichia coli, Escherichia coli Proteins, Escherichia coli Proteins: chemistry, Escherichia coli Proteins: genetics, Escherichia coli Proteins: metabolism, Escherichia coli: enzymology, Evolution, Molecular, Multienzyme Complexes, Multienzyme Complexes: chemistry, Multienzyme Complexes: genetics, Multienzyme Complexes: metabolism, Mutagenesis, Mutant Proteins, Mutant Proteins: genetics, Mutant Proteins: metabolism, Protein Kinases, Protein Kinases: genetics, Protein Kinases: metabolism, Protein Multimerization, Protein Structure, Site-Directed, Tertiary

Two-component signal transduction pathways consisting of a histidine kinase and a response regulator are used by prokaryotes to respond to diverse environmental and intracellular stimuli. Most species encode numerous paralogous histidine kinases that exhibit significant structural similarity. Yet in almost all known examples, histidine kinases are thought to function as homodimers. We investigated the molecular basis of dimerization specificity, focusing on the model histidine kinase EnvZ and RstB, its closest paralog in Escherichia coli. Direct binding studies showed that the cytoplasmic domains of these proteins each form specific homodimers in vitro. Using a series of chimeric proteins, we identified specificity determinants at the base of the four-helix bundle in the dimerization and histidine phosphotransfer domain. Guided by molecular coevolution predictions and EnvZ structural information, we identified sets of residues in this region that are sufficient to establish homospecificity. Mutating these residues in EnvZ to the corresponding residues in RstB produced a functional kinase that preferentially homodimerized over interacting with EnvZ. EnvZ and RstB likely diverged following gene duplication to yield two homodimers that cannot heterodimerize, and the mutants we identified represent possible evolutionary intermediates in this process.