Student Theses and Dissertations

Date of Award


Document Type


RU Laboratory

Muir Laboratory


histidine kinase, ligand-induced signal transduction, AgrC, quorum sensing, Staphylococcus aureus


Bacteria use receptor histidine kinases to sense extracellular cues and convert them into intracellular signaling events that allow them to respond to their environment. In Staphylococcus aureus, each individual cell must sense the size of its overall population in order to synchronize virulence factor expression with the entire population. This task is carried out by the accessory gene regulator (agr) quorum sensing system. The agr autoinducing peptide (AIP) pheromone activates the AgrC receptor histidine kinase, resulting in downstream modulation of virulence factor expression. As S. aureus is a dangerous pathogen, understanding virulence regulation is of great interest, and the agr system has been extensively studied. However, little was known about the mechanism of ligand-induced signal transduction by AgrC at the outset of this work. Moreover, AgrC is member of a unique class of histidine kinases, for which the activation mechanisms are equally speculative, although several of these receptors function in important quorum sensing processes. The aim of this work was to elucidate molecular mechanisms of AIP–AgrC signaling, focusing on inhibitor structure– activity relationships and understanding how ligand binding results in AgrC kinase activation. A new Fmoc-based synthetic route to AIPs and 􀀁-thioester peptides was developed and used to construct a series of inhibitor AIPs to define the minimal inhibitory pharmacophore. The minimized scaffold should provide a foundation for future medicinal chemistry efforts. The AgrC activation mechanism was probed via direct biochemical analysis of the receptor, which was previously unattainable, and mutagenesis. The results indicate that AgrC is a dimer and trans-autophosphorylates and that signal transduction occurs symmetrically within the dimer due to intermolecular conformational changes. This mechanism may be a general means by which dimeric quorum sensing receptors rapidly elicit a response upon signal detection.


A thesis presented to the faculty of The Rockefeller University in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

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