Date of Award

5-2023

Document Type

Honors Thesis

Degree Name

Bachelor of Science

Department

Biological Science

Advisor/Committee Chair

Jon Paczkowski

Major

Biochemistry and Molecular Biology

Abstract

Pseudomonas aeruginosa is a bacterium capable of causing disease in immunocompromised individuals and individuals with underlying lung disorders. It controls the expression of a subset of its genes through quorum sensing, which is a cell-cell communication system involved in mediating the transition from individual to group behaviors. Group behaviors are cellular processes undertaken by the cell that are beneficial to the collective, such as biofilm formation – a key component of pathogenesis in the human lung. They rely on the production, accumulation, detection, and response to signal molecules called autoinducers. There are two acyl-homoserine lactone autoinducer quorum sensing systems in P. aeruginosa that are responsible for the transition to group behaviors: the Las system and Rhl system. The systems contain LasR and RhlR, respectively, which are transcriptional activator proteins known as LuxR-type proteins, as well as LasI and RhlI, which synthesize the respective autoinducers for LasR and RhlR. RhlR directly interacts with another protein called PqsE to control RhlR-dependent transcription. To study whether or not the mechanism of activation between RhlR and PqsE is conserved in other pathogenic bacteria, the interactions of PqsE with LuxR-type receptors from other organisms were assessed. This included SdiA from Salmonella enterica and CviR from Chromobacterium violaceum. Through a protein pulldown experiment, it was determined that PqsE did not interact with LasR, SdiA, or CviR, and a light assay confirmed these results, indicating that the P. aeruginosa PqsE specifically evolved to interact with its paired receptor, RhlR. Burkholderia cepacia is a bacterium that is similar to P. aeruginosa; it has both PqsE and RhlR homologs (referred to as PqsE and SolR, respectively). With the structure and function of RhlR and PqsE recently determined, we now aimed to determine the function of SolR and PqsE to understand the molecular basis for the evolution of the PqsE-quorum-sensing receptor interactions. A bioinformatics approach was taken using a machine learning program called Alphafold to analyze the structure of SolR and PqsE. It was determined that PqsE from B. cepacia does not dimerize like PqsE from P. aeruginosa, which altered its ability to interact with its potential binding partner, SolR. Future experiments will focus on biochemical assessment of SolR and PqsE from B. cepacia.

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