Structural basis for antiactivation in bacterial quorum sensing

Abstract

Bacteria can communicate via diffusible signal molecules they generate and release to coordinate their behavior in response to the environment. Signal molecule concentration is often proportional to bacterial population density, and when this reaches a critical concentration, reflecting a bacterial quorum, specific behaviors including virulence, symbiosis, and horizontal gene transfer are activated. Quorum-sensing regulation in many Gramnegative bacteria involves acylated homoserine lactone signals that are perceived through binding to LuxR-type, acylated-homoserine-lactone-responsive transcription factors. Bacteria of the rhizobial group employ the LuxR-type transcriptional activator TraR in quorum sensing, and its activity is further regulated through interactions with the TraM antiactivator. In this study, we have crystallographically determined the 3D structure of the TraR-TraM antiactivation complex from Rhizobium sp. strain NGR234. Unexpectedly, the antiactivator TraM binds to TraR at a site distinct from its DNA-binding motif and induces an allosteric conformational change in the protein, thereby preventing DNA binding. Structural analysis reveals a highly conserved TraR-TraM interface and suggests a mechanism for antiactivation complex formation. This structure may inform alternative strategies to control quorumsensing-regulated microbial activity including amelioration of infectious disease and antibiotic resistance. In addition, the structural basis of antiactivation presents a regulatory interaction that provides general insights relevant to the field of transcription regulation and signal transduction.crystal structure ͉ TraR-TraM complex ͉ allosteric mechanism ͉ protein-protein interaction ͉ signal transduction

Crystal structure of QscR, aPseudomonas aeruginosaquorum sensing signal receptor

“…The antiactivator protein, TraM, inhibits the DNA binding of TraR (30,31). Structures of the TraR-3OC8-HSL-TraM complex showed that TraM binds between the LBD and DBD in a symmetric configuration, making numerous contacts with DBD, LBD, and the linker between them, which places the DBDs in a position that is incompetent to bind to DNA (13,(32)(33)(34). Because TraM can form a complex with TraR while it is simultaneously bound to DNA (34), it is quite unlikely that TraR adopts a crosssubunit architecture, and indeed the linker of TraR probably evolved to bind to TraM and not necessarily to make the extensive interactions with the LBD or DBDs that have been observed in the QscR or CviR structures (16).…”

ExsD Inhibits Expression of thePseudomonas aeruginosaType III Secretion System by Disrupting ExsA Self-Association and DNA Binding Activity

“…Antiactivators from other systems (non-AraC targets) function by one of three mechanisms: preventing self-association of the activator (5), occluding the DNA binding domain from interacting with DNA (19,22,24), or inducing conformational changes that alter the structure of the DNA binding domain (6). ExsD inhibits ExsA-dependent transcription by employing at least two of these mechanisms.…”

Cell-Cell Communication in Bacteria: United We Stand

“…S2:2), revealed new structural insights into TraM/TraR associations and inhibition of premature TraR activity based on the more structurally tractable TraM/TraR NGR antiactivator complex of Rhizobium sp. strain NGR234 (18). These studies provide evidence for an allosteric mechanism (Fig.…”