The inhibitory form of NifL from Klebsiella pneumoniae exhibits ATP hydrolyzing activity only when synthesized under nitrogen sufficiency

The NifL-NifA System: a Multidomain Transcriptional Regulatory Complex That Integrates Environmental Signals

“…Although both of these forms are competent to inhibit Kp NifA in vitro, an increase in inhibitory activity is observed in the presence of adenosine nucleotides. Surprisingly however, nucleotide binding to Kp NifL is apparently associated with the PAS1 domain and not with the C-terminal GKHL-like domain (56). The sequences required for the interaction between Kp NifL and Kp NifA also appear to be different than the sequences required in the A. vinelandii NifL-NifA system.…”

“…In contrast to Av NifL, the presence of adenosine nucleotides is not specifically required for the inhibition of Kp NifA activity by Kp NifL (57). Although neither ATP hydrolysis (10) nor kinase activities (87) have been reported previously, Kp NifL has recently been shown to exhibit ATP binding and ATPase activity when it is purified from cultures grown under conditions of nitrogen sufficiency (56). In contrast, Kp NifL purified from cultures grown under conditions of nitrogen deficiency is catalytically inactive.…”

“…Av NifL contains conserved residues corresponding to the N, G1, F, and G2 boxes that constitute the ATP binding domain of the GHKL superfamily, and this domain of Av NifL has been demonstrated to bind adenosine nucleotides (93) (see below). However, the corresponding region of Kp NifL is less homologous to the GHKL superfamily and apparently does not bind nucleotides (56). Structural predictions also indicate that the region of Av NifL located between the PAS2 and GHKL domains may constitute an antiparallel helix bundle, similar to the structures of the dimerization (H) domains of the HPKs EnvZ and CheA.…”

“…This activity was detected only when NifL was purified from cells grown under nitrogen-sufficient conditions (56).…”

“…This activity was detected only when NifL was purified from cells grown under nitrogen-sufficient conditions (56). e Wild-type Kp NifL is competent to inhibit Kp NifA in response to fixed nitrogen and oxygen in vivo (46,66).…”