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Journal Of Biological Chemistry


Autoinducer-2 (AI-2) is unique among quorum-sensing signaling molecules, as it is produced and recognized by a wide variety of bacteria and thus facilitates interspecies communication. To date, two classes of AI-2 receptors have been identified: the LuxP-type, present in the Vibrionales, and the LsrB-type, found in a number of phylogenetically distinct bacterial families. Recently, AI-2 was shown to affect the colonization levels of a variety of bacteria in the microbiome of the mouse gut, including members of the genus Clostridium, but no AI-2 receptor had been identified in this genus. Here, we identify a noncanonical, functional LsrB-type receptor in Clostridium saccharobutylicum. This novel LsrB-like receptor is the first one reported with variations in the binding-site amino acid residues that interact with AI-2. The crystal structure of the C. saccharobutylicum receptor determined at 1.35 Å resolution revealed that it binds the same form of AI-2 as the other known LsrB-type receptors, and isothermal titration calorimetry (ITC) assays showed that binding of AI-2 occurs at a submicromolar concentration. Using phylogenetic analysis, we inferred that the newly identified noncanonical LsrB receptor shares a common ancestor with known LsrB receptors and that noncanonical receptors are present in bacteria from different phyla. This led us to identify putative AI-2 receptors in bacterial species in which no receptors were known, as in bacteria belonging to the Spirochaetes and Actinobacteria phyla. Thus, this work represents a significant step toward understanding how AI-2–mediated quorum sensing influences bacterial interactions in complex biological niches.


quorum sensing, isothermal titration calorimetry (ITC), microbiome, cell signaling, crystal structure, ABC transporters, autoinducer-2, Clostridium autoethanogenum, Clostridium saccharobutylicum, LsrB receptors


This research was originally published in the Journal of Biological Chemistry. Inês M. Torcato, Meghann R. Kasal, Patrícia H. Brito, Stephen T. Miller, and Karina B. Xavier. Identification of novel autoinducer-2 receptors in Clostridia reveals plasticity in the binding site of the LsrB receptor family. J Biol Chem. 2019; 294:4450-4463. © 2019 Torcato et al.

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