Mechanisms of acid protection mediated by periplasmic chaperones in Escherichia coli

• Main Author: Harding, Amanda
• Published: University of Aberdeen 2009
• Subjects: 571.29; Escherichia coli
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.499690

HdeA and HdeB are stationary phase periplasmic proteins believed to function as acid-induced chaperones to prevent the aggregation of periplasmic proteins at low pH.  The aims of this project were to examine the importance of HdeA and HdeB for <i>E. coli</i> acid resistance, to determine the fate of periplasmic proteins at acid pH and to establish the extent to which HdeA and HdeB aid protein stability during an acid challenge. This study has demonstrated that HdeA and HdeB are important for acid resistance, but to a lesser extent than is currently described in the literature.  The work presented in this thesis shows that <i>hdeAB </i>mutants retained a degree of acid resistance, albeit at a lower level than the wild type strains.  HdeA and HdeB contribute to, but are not essential for acid resistance.  The temperature at which cells were grown and subsequently acid challenged at was also shown to be an important factor in acid resistance. Cytoplasmic and exponential phase periplasmic proteins were found to be acid sensitive and aggregated after treatment at acid pH.  In contrast, stationary phase periplasmic proteins were resistant to aggregation at acid pH.  The absence of HdeA and HdeB from stationary phase periplasmic extracts did not result in protein aggregation.  This demonstrated that HdeA and HdeB are not required for protein stability at acid pH.  An exception to this was the periplasmic protein, FkpA, which was found to precipitate upon acid treatment in the absence of HdeA and HdeB.  This presented a potential role for HdeA and HdeB in stabilising FkpA upon exposure to acid pH.