Structure-Based Insights into the Molecular Mechanisms of LuxR-Type Quorum Sensing Receptors

Quorum sensing (QS) enables bacteria to coordinate collective behaviors in response to population density. LuxI/R QS systems, common among gram-negative bacteria, consist of a LuxI-type synthase that produces an N- acyl l -homoserine lactone (AHL) signaling molecule and a LuxR-type receptor that senses the AHL. At threshold AHL concentrations, LuxR-type receptors undergo ligand-induced conformational changes that affect DNA binding and target gene transcription. Because of their role in regulating myriad collective behaviors, LuxI/R systems are targets for many applications, including antivirulence strategies and the engineering of beneficial microbiomes. Recent structural studies have led to substantial progress in understanding molecular mechanisms of LuxI/R systems. However, LuxR-type receptors fall into functionally diverse subfamilies for which structural bases remain incompletely understood. In this article, we summarize recent structural and mechanistic insights into LuxR-type receptor function, including interactions with small molecules, protein partners, and DNA. We identify critical knowledge gaps that highlight the need for additional structural and mechanistic information regarding LuxI/R QS.