Quality control of a molybdoenzyme by the Lon protease

•The stability of the TorA molybdoenzyme depends on TorD, its specific chaperone.•Lon protease degrades the immature form of TorA in the absence of TorD.•Lon and TorD compete for TorA binding.•Lon regulates the amount of immature TorA.•This is the first evidence for a molybdoenzyme degradation pathway.

Molybdoenzymes contain a molybdenum cofactor in their active site to catalyze various redox reactions in all domains of life. To decipher crucial steps during their biogenesis, the TorA molybdoenzyme of Escherichia coli had played a major role to understand molybdoenzyme maturation process driven by specific chaperones. TorD, the specific chaperone of TorA, is also involved in TorA protection. Here, we show that immature TorA (apoTorA) is degraded in vivo and in vitro by the Lon protease. Lon interacts with apoTorA but not with holoTorA. Lon and TorD compete for apoTorA binding but TorD binding protects apoTorA against degradation. Lon is the first protease shown to eliminate an immature or misfolded molybdoenzyme probably by targeting its inactive catalytic site.

Structured summary of protein interactionsLoncleavesapoTorA by enzymatic study (View interaction)apoTorAbinds to Lon by surface plasmon resonance (View interaction)