Colicins are a type of bacterial toxin produced by Escherichia coli to kill E. coli
and closely related bacteria. In contrast to the protein secretion pathway, colicins are
released into the extracellular environment due to lysis of the cell. The colicins then
enter the target bacterial cell by binding to a surface receptor (ex. BtuB) and
translocating through an outer membrane channel (ex. OmpF) which is facilitated by the
interaction with the Tol proteins. Once inside the target cell, pore-forming colicins form
membrane channels in the inner membrane whereas enzymatic colicins enter the
cytoplasm to degrade the DNA or RNA. The mechanism used by enzymatic colicins to
enter the cytoplasm is still unknown and is the focus of my project.
Cim (cytoplasmic import) mutants were previously discovered in the Benedik
lab. These mutants are resistant to enzymatic colicins (E2 and E3) but sensitive to pore
forming colicins (A and E1). It was determined that this phenotype was due to a single
nucleotide substitution resulting in an amino acid change in tolB.
The focus of my project was to understand the phenotype of the cim mutants so
that I could gain more insight regarding the import of enzymatic colicins. To do this I constructed colicin hybrids by swapping the T-R domains with the A-I domains of
colicins A, E1, and E2. With these hybrids I was able to test whether an enzymatic
colicin that was coupled with a pore-forming colicin would be functional or not. The
lack of activity in these hybrids may be due to a lack of essential recognition elements
used by enzymatic colicins and not possessed by pore-forming colicins.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-2321 |
| Date | 15 May 2009 |
| Creators | Charles, Tysheena Perkins |
| Contributors | Benedik, Michael |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Thesis, text |
| Format | electronic, application/pdf, born digital |
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