A Mutation in the N Domain of Escherichia coli Lon Stabilizes Dodecamers and Selectively Alters Degradation of Model Substrates
Article (Web of Science)
ABSTRACTEscherichia coli
Lon, an ATP-dependent AAA
+
protease, recognizes and degrades many different substrates, including the RcsA and SulA regulatory proteins. More than a decade ago, the E240K mutation in the N domain of Lon was shown to prevent degradation of RcsA but not SulA
in vivo
. Here, we characterize the biochemical properties of the E240K mutant
in vitro
and present evidence that the effects of this mutation are complex. For example, Lon
E240K
exists almost exclusively as a dodecamer, whereas wild-type Lon equilibrates between hexamers and dodecamers. Moreover, Lon
E240K
displays degradation defects
in vitro
that do not correlate in any simple fashion with degron identity, substrate stability, or dodecamer formation. The Lon sequence segment near residue 240 is known to undergo nucleotide-dependent conformational changes, and our results suggest that this region may be important for coupling substrate binding with allosteric activation of Lon protease and ATPase activity.
