CnoX Is a Chaperedoxin: A Holdase that Protects Its Substrates from Irreversible Oxidation

Bleach (HOCl) is a powerful oxidant that kills bacteria in part by causing protein aggregation. It inactivates ATP-dependent chaperones, rendering cellular proteins mostly dependent on holdases. Here we identified Escherichia coli CnoX (YbbN) as a folding factor that, when activated by bleach via chlorination, functions as an efficient holdase, protecting the substrates of the major folding systems GroEL/ES and DnaK/J/GrpE. Remarkably, CnoX uniquely combines this function with the ability to prevent the irreversible oxidation of its substrates. This dual activity makes CnoX the founding member of a family of proteins, the "chaperedoxins." Because CnoX displays a thioredoxin fold and a tetratricopeptide (TPR) domain, two structural motifs conserved in all organisms, this investigation sets the stage for the discovery of additional chaperedoxins in bacteria and eukaryotes that could cooperate with proteins from both the Hsp60 and Hsp70 families.