Two‐component signaling in the AAA+ ATPase DctD: binding Mg2+and BeF3selects between alternative dimeric states of the receiver domain

Abstract
SPECIFIC AIMThe DctD protein of Sinorhizobium meliloti DctD is a σ54- or σN-dependent enhancer binding protein (EBP) essential for symbiotic biological nitrogen fixation. Its central AAA+ ATPase domain is regulated by phosphorylation of an amino-terminal, two-component receiver domain. A novel dimeric receiver domain structure has been described. Its subunit interface consists of contacts along the α4–β5–α5 surface and includes contributions from a pseudo coiled coil made by extending helix α5 well into the adjacent linker that joins the receiver and ATPase domains. The integrity of this dimer interface was seen to be essential for inhibiting oligomeric assembly of the AAA+ ATPase into an active form, thus defining the “off-state” of the protein. Moreover, analytical ultracentrifugation data showed that phosphorylation altered the dimeric state but did not destabilize it. The aim of the present study was to compare the “activated” structure of the S. meliloti DctD receiver domain (N) and linker (L; hereaf...
Funding Information
  • National Institutes of Health (RR 11318)