Formation of a distinctive complex between the inducible bacterial lysine decarboxylase and a novel AAA+ ATPase

AAA+ ATPases are ubiquitous proteins that employ the energy obtained from ATP hydrolysis to remodel proteins, DNA, or RNA. The MoxR family of AAA+ proteins is widespread throughout bacteria and archaea but is largely uncharacterized. Limited work with specific members has suggested a potential role as molecular chaperones involved in the assembly of protein complexes. As part of an effort aimed at determining the function of novel AAA+ chaperones in Escherichia coli, we report the characterization of a representative member of the MoxR family, YieN, which we have renamed RavA (regulatory ATPase variant A). We show that the ravA gene exists on an operon with another gene encoding a protein, YieM, of unknown function containing a Von Willebrand Factor Type A domain. RavA expression is under the control of the sigmaS transcription factor, and its levels increase toward late log/early stationary phase, consistent with its possible role as a general stress-response protein. RavA functions as an ATPase and forms hexameric oligomers. Importantly, we demonstrate that RavA interacts strongly with inducible lysine decarboxylase (LdcI or CadA) forming a large cage-like structure consisting of two LdcI decamers linked by a maximum of five RavA oligomers. Surprisingly, the activity of LdcI does not appear to be affected by binding to RavA in a number of in vitro and in vivo assays, however, complex formation results in the stimulation of RavA ATPase activity. Data obtained suggest that the RavA-LdcI interaction may be important for the regulation of RavA activity against its targets.