Snapshots of conformational changes shed light into the NtrX receiver domain signal transduction mechanism (ARTICULO DESTACADO COMO TAPA DE REVISTA)

IGNACIO FERNÁNDEZ; LISANDRO OTERO; SEBASTIÁN KLINKE; MARIELA DEL C. CARRICA; FERNANDO A. GOLDBAUM

JOURNAL OF MOLECULAR BIOLOGY

ACADEMIC PRESS LTD-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2015 vol. 427 p. 3258 - 3272

0022-2836

Brucella abortus is an important pathogenic bacterium that has to overcome oxygen deficiency in order to achieve a successful infection. Previously, we proved that a two-component system formed by the histidine kinase NtrY and the response regulator NtrX is essential to achieve an adaptive response to low oxygen tension conditions. Despite that the relevance of this signaling pathway has already been demonstrated in other microorganisms, its molecular activation mechanism has not been described in detail yet. In this article, we report the first crystal structures of the NtrX receiver domain from Brucella abortus under different conformations, and propose a sequence of events to explain the structural rearrangements along the activation process. The analysis of the structures obtained in the presence of the phosphoryl group analog beryllofluoride led us to postulate that changes in the interface formed by the alpha-4 helix and the beta-5 strand are important for the activation, producing a reorientation of the alpha-5 helix. Also, a biochemical characterization of the NtrX receiver domain enzymatic activities was performed, describing its autophosphorylation and autodephosphorylation kinetics. Finally, the role of H85, an important residue, was addressed by site-directed mutagenesis.Overall, these results provide significant structural basis for understanding the response regulator activation in this bacterial two-component system.