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Chapter 9 : LuxR-Type Proteins in Pseudomonas aeruginosa Quorum Sensing: Distinct Mechanisms with Global Implications
Category: Microbial Genetics and Molecular Biology; Bacterial Pathogenesis
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LuxR-Type Proteins in Pseudomonas aeruginosa Quorum Sensing: Distinct Mechanisms with Global Implications, Page 1 of 2< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555815578/9781555814045_Chap09-1.gif /docserver/preview/fulltext/10.1128/9781555815578/9781555814045_Chap09-2.gif
The opportunistic pathogen Pseudomonas aeruginosa provides one of the most intensely studied examples of acylhomoserine lactone (acyl-HSL)-controlled gene expression. In P. aeruginosa, quorum-sensing gene regulation is accomplished by two complete acyl-HSL systems, LasR-LasI and RhlR-RhlI, and by an orphan receptor, QscR. One microarray study provided additional insights into the signal requirements for the activation of individual quorum-controlled genes. LuxR-type polypeptides can be subdivided into two functional domains based on sequence conservation, genetic and biochemical analysis of representative members, and the crystal structure of TraR from Agrobacterium tumefaciens. LuxR-type proteins also contain a helix-turn-helix motif (HTH) in their carboxy-terminal domain that is required for DNA binding. Based on the recent biochemical characterization of other LuxR-type proteins, general patterns of acyl-HSL/receptor interaction emerge that allow us to distinguish three separate classes. The three P. aeruginosa receptors LasR, RhlR, and QscR each represent one such class: LasR is a class 1 receptor. In contrast, if LuxR-type proteins such as LasR and QscR require their ligand for proper folding, they should induce transcription of target genes relatively slowly because protein activation through translation would be slow. Once a quorum is reached, a change in the gene expression profile is triggered that leads to the formation of a mature biofilm, reminiscent of a developmental program in more complex systems.
Structure and function of LuxR-type transcription factors. (A) Key regions based on sequence conservation, biochemical analysis of LuxR, TraR and other family members, and the recent TraR crystal structure. The indicated multimerization region has been genetically defined as being required for LuxR multimerization. Several details mentioned in the text are not included in this cartoon. (B) A 3-oxo-C8-HSL molecule showing the specific TraR residues that are thought to coordinate each position of this acyl-HSL (Tyr61 interacts along the acyl chain). (C) The palindromic tra box (the DNA-binding site for TraR) is shown with the two residues (Arg206 and Arg210) that make specific base contacts with this site. Symmetrical contacts are made with the DNA sequence in each half-site.
Characteristics of acyl-HSL/LuxR-type receptor interaction