Three-dimensional structure of full-length NtrX, an unusual member of the NtrC family of response regulators

IGNACIO FERNÁNDEZ; IRINA CORNACIU; MARIELA DEL CARMEN CARRICA; EMIKO UCHIKAWA; GUILLAUME HOFFMANN; RODRIGO SIEIRA; JOSÉ ANTONIO MÁRQUEZ; FERNANDO A. GOLDBAUM

JOURNAL OF MOLECULAR BIOLOGY

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2017

0022-2836

p { margin-bottom: 0.1in; direction: ltr; color: rgb(0, 0, 10); line-height: 120%; text-align: left; }p.western { font-family: "Calibri",serif; font-size: 11pt; }p.cjk { font-family: "Calibri"; font-size: 11pt; }p.ctl { font-family: "Times New Roman"; font-size: 11pt; }a:link { color: rgb(0, 0, 255); }a.ctl:link { font-family: "Times New Roman"; }Bacteriasense and adapt to environmental changes using two-component systems(TCS). These signaling pathways are formed by a histidine kinase (HK)that phosphorylates a response regulator (RR), which finallymodulates the transcription of target genes.Thebacterium Brucellaabortuscodes for a TCS formed by the HK NtrY and the RR NtrX thatparticipates in sensing low oxygen tension and in generating anadaptive response. NtrX is a modular protein with REC, AAA+ and DNAbinding domains, an architecture that classifies it among the NtrCsubfamily of RRs. However, it lacks a signature motif essential foractivating transcription by the mechanism proposed for canonicalmembers of this subfamily. In this article we present the firstcrystal structure of full-length NtrX, which is alsothe first structure of a full-length NtrC-like RR with all thedomains solved, showingthat the protein is structurally similar to other members of thesubfamily. Wealso report that NtrX binds nucleotides and the structures of theprotein bound to ATP or ADP. Despite binding ATP, NtrX does not haveATPase activity and does not form oligomers in response tophosphorylation or nucleotide binding. We also identify a nucleotidesequence recognized by NtrX that allows it to bind to a promoterregion that regulates its own transcription and to establish anegative feedback mechanism to modulate its expression. Overall, thisarticle provides a detailed description of the NtrX RR and supportsthat it might function by a mechanism different to classicalNtrC-like RRs.