Secretion Kinetics of Salmonella Effector Proteins and Their Homologs

Undergraduate Honors Thesis

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Citeable URL: https://scholar.colorado.edu/concern/undergraduate_honors_theses/3r074w514

Abstract

The Type III Secretion System (T3SS) is a needle-like assembly that bacteria such as Salmonella use to put their infectious proteins in target cells. The proteins that are put through the T3SS are the focus of this study because they have an interesting evolutionary pressure. The T3SS is one amino acid wide, so any proteins that go through it must be unfolded before being excreted. This project studies how the proteins have evolved to be unfolded. Whether they have evolved to be mechanically labile or not. This study is done by putting a tag on a protein that is normally excreted by the T3SS and a tag on a protein that is homologous to the first, but is not normally excreted by the T3SS. The tag is able to go through the T3SS and will bind a fluorescent molecule that is membrane-permeable. The end-goal is to do an infection assay where the proteins will be highly concentrated proteins within the bacterial cells, causing a large fluorescence reading. When the proteins are excreted into the mammalian cells, their fluorescence readings will decrease because they become less concentrated. This decrease in fluorescence will be related to the secretion rate of the proteins. Based on those readings, it can be concluded whether or not the traditionally secreted proteins are more easily excreted compared to the non-traditionally secreted ones.

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