![]() coli Hsp90 interacts with selected candidates and demonstrated Hsp90's role in flagellar motility and chemotaxis. Many of the putative clients were involved in flagellar assembly, suggesting a crucial role of Hsp90 in the regulation of bacterial motility. We extended our analysis to identify genes that exhibit evolutionary dynamics characteristic of Hsp90 clients. We found that Hsp90 co-evolves with membrane-associated protein complexes such as the flagellum and that Hsp90 is associated with a preference for inhabiting multiple habitats. These genes provide insights into potential functions of Hsp90 in bacteria. To address this challenge, we analyzed the presence and absence of thousands of genes across numerous bacterial species and identified genes that co-evolved with Hsp90. Although Hsp90 is well-studied in eukaryotic species from yeast to humans, little is known about its counterpart in bacteria. Hsp90 is particularly important when organisms are under environmental or mutational stress (e.g. Hsp90 is a chaperone protein that aids the folding of many other proteins (clients), which tend to be signal transduction proteins. Taken together, our results reveal previously unknown functions of bacterial Hsp90 and open avenues for future experimental exploration by implicating Hsp90 in the assembly of membrane protein complexes and adaptation to novel environments. This novel function of bacterial Hsp90 agreed with our subsequent finding that Hsp90 is associated with a preference for multiple habitats and may therefore face a complex selection regime. Furthermore, normal Hsp90 function is important for wild-type motility and/or chemotaxis in E. ![]() We validated our predictions by demonstrating that the flagellar protein FliN and the chemotaxis kinase CheA behaved as Hsp90 clients in Escherichia coli, confirming the predicted role of Hsp90 in chemotaxis and flagellar assembly. To add to the limited set of known bacterial Hsp90 clients, we further developed a statistical method to predict putative clients. ![]() We find that genes whose gain and loss were coordinated with Hsp90 throughout bacterial evolution tended to function in flagellar assembly, chemotaxis, and bacterial secretion, suggesting that Hsp90 may aid assembly of protein complexes. To enable such characterization, we used a genome-scale phylogenetic analysis to identify genes that co-evolve with bacterial Hsp90. ![]() In contrast, Hsp90 is not essential in bacteria, and a broad characterization of its molecular and organismal function is lacking. The molecular chaperone Hsp90 is essential in eukaryotes, in which it facilitates the folding of developmental regulators and signal transduction proteins known as Hsp90 clients. ![]()
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