J-Domain Proteins in Bacteria and Their Viruses.

Molecular chaperones maintain cellular protein homeostasis by acting at almost every step in protein biogenesis pathways. The DnaK/HSP70 chaperone has been associated with almost every known essential chaperone functions in bacteria. To act as a bona fide chaperone, DnaK strictly relies on essential co-chaperone partners known as the J-domain proteins (JDPs, DnaJ, Hsp40), which preselect substrate proteins for DnaK, confer its specific cellular localization, and stimulate both its weak ATPase activity and substrate transfer. Remarkably, genome sequencing has revealed the presence of multiple JDP/DnaK chaperone/co-chaperone pairs in a number of bacterial genomes, suggesting that certain pairs have evolved toward more specific functions. In this review, we have used representative sets of bacterial and phage genomes to explore the distribution of JDP/DnaK pairs. Such analysis has revealed an unexpected reservoir of novel bacterial JDPs co-chaperones with very diverse and unexplored function that will be discussed.