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Interaction and localisation studies of the lipoteichoic acid synthesis proteins in staphylococcus aureus

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Title: Interaction and localisation studies of the lipoteichoic acid synthesis proteins in staphylococcus aureus
Authors: Reichmann, Nathalie
Item Type: Thesis or dissertation
Abstract: Lipoteichoic acid (LTA) is an important component of the cell envelope of various Gram-positive bacteria. In Staphylococcus aureus it consists of a polyglycerolphosphate chain that is decorated with D-alanine esters and anchored to the cell membrane via a glycolipid. The lack of D-alanine modifications leads to increased susceptibility to cationic antimicrobial peptides and the complete absence of LTA results in aberrant positioning of septa, enlargement of cells and eventual cell lysis, indicating a link between LTA synthesis and cell division. Although key enzymes required for LTA synthesis and D-alanylation have been identified, the full process has not been elucidated and is investigated in this study. Using a bacterial two-hybrid approach it was shown that the three key LTA synthesis enzymes, YpfP, LtaA and LtaS, interact with one another, indicating the formation of a multi-enzyme complex. In addition, these three proteins interacted with numerous cell division and peptidoglycan synthesis proteins. Fluorescence microscopy studies indicated that YpfP and LtaA localise to the membrane, while LtaS appeared to accumulate at the site of cell division in cells with fully formed septa. Together, these data provide further experimental evidence for the coordination between the processes of cell division and LTA synthesis. Four proteins, DltA-D, are essential for the D-alanylation of LTA. The mechanism begins with DltA transferring D-alanines onto the carrier protein DltC. However, Fischer and colleagues, and Neuhaus and Baddiley have proposed two conflicting models for the remainder of the mechanism for D-alanylation. Here, using a cellular protein localisation analysis it was shown that DltC does not traverse the membrane and membrane topology studies indicated that DltD is anchored to the outside of the cell, contrary to the Neuhaus and Baddiley model. In summary, the data presented in this study are in support of the D-alanine substitution model proposed by Werner Fischer.
Content Version: Open access
Issue Date: Sep-2012
Date Awarded: Mar-2013
URI: http://hdl.handle.net/10044/1/39406
DOI: https://doi.org/10.25560/39406
Supervisor: Grundling, Angelika
Sponsor/Funder: Biotechnology and Biological Sciences Research Council (Great Britain)
Department: Medicine
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Appears in Collections:Medicine PhD theses

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