Invited
Investigating the principles of operation of biomolecular machines – one molecule at a time

Aggregated proteins are highly toxic to the cell, and are involved in the pathophysiology of multiple diseases, in particular neurodegenerative diseases. The bacterial protein ClpB (caseinolytic peptidase B) acts to rescue proteins from aggregates. This fascinating ATP-dependent hexamer resolubilizes aggregated polypeptides in cooperation with the co-chaperone DnaK, which binds to its so-called Middle Domain (M domain). It was proposed that the M domain functions as a switch of the machine, but the mechanism by which this regulatory domain affects disaggregation remains elusive.

Here we used the powerful tool of single-molecules fluorescence to monitor the dynamics of the M domain. Surprisingly, we find it to jump between two major states on the microsecond time scale, several orders of magnitude faster than ClpB’s functional cycle. The relative population of the two states of the M domain varies continuously in response to several internal and external cues, providing a dynamic control signal to ClpB. This mode of control enables fast adaptation to cellular needs and may be a general mechanism for the regulation of cellular machineries.