Date of Award

Spring 2014

Document Type

Restricted Thesis

Terms of Use

© 2014 Samuel E. Tanner. All rights reserved. Access to this work is restricted to users within the Swarthmore College network and may only be used for non-commercial, educational, and research purposes. Sharing with users outside of the Swarthmore College network is expressly prohibited. For all other uses, including reproduction and distribution, please contact the copyright holder.

Degree Name

Bachelor of Arts


Chemistry & Biochemistry

First Advisor

Stephen T. Miller


Quorum sensing is a process in which bacteria coordinate gene expression in a cell-density dependent manner. Quorum sensing is facilitated by the secretion and importation of small signaling molecules called autoinducers. One class of autoinducer, termed autoinducer-2 (AI-2), facilitates interspecies communication. AI-2 consists of a set of interconverting derivatives of 4,5-dihydroxy-2,3-pentadione (DPD). In Escherichia coli and Salmonella typhimurium, AI-2 is internalized and processed by the proteins encoded for by the lsr operon. This process is thought to disrupt communication networks of neighboring species and therefore provide an evolutionary advantage. Since AI-2 signaling has been implicating in the coordinated gene expression of biofilm formation and virulent factors in several species, elucidating the mechanism by which bacteria process AI-2 could have several biotechnological and medical applications. In this study, I investigate two proteins on the lsr operon: LsrG and LsrE. LsrG has been shown to isomerize the phosphorylated version of AI-2 (P-AI-2) but the mechanism by which this reaction occurs is unknown. Therefore, I probe the putative active site of LsrG by x- ray crystallography and the creation of novel point mutants. LsrE is a nonconserved protein of the lsr operon that has not been characterized in vitro. I present the first attempts at expressing and purifying LsrE in high yield and purity for in vitro assays and x-ray crystallography.