Dissertations and Theses

Date of Award

2018

Document Type

Thesis

Department

Biology

First Advisor

Anuradha Janakiraman

Second Advisor

Christine Li

Third Advisor

Shireen Saleque

Keywords

cell envelope, membrane integrity, membrane biogenesis, protein biogenesis, lipoprotein

Abstract

One of the distinct characteristics of Gram-negative bacteria such as Escherichia coli is the possession of a double-membraned cell envelope. The outer membrane provides an additional layer of protection against hydrophobic molecules including antibiotics, contributing to the multidrug resistance crisis. The Gram-negative membrane is composed of phospholipids, glycolipids, and proteins. A large portion of the bacterial cellular proteome is composed of membrane proteins. Despite this, the functions of several membrane proteins are as yet undefined. Therefore, defining the physiological roles of uncharacterized membrane proteins is expected to provide us with insights into the biology of the Gram-negative cell envelope and to perhaps address aspects of bacterial multidrug resistance. In this thesis, I have characterized the genetic phenotypes of a predicted inner membrane lipoprotein of unknown function in E. coli, a model Gram-negative bacterium. The deletion of this putative lipoprotein confers pleiotropic phenotypes such as a reduction in cellular viability, morphology defects, and sensitivity to detergents and copper ions. The cell envelope stress response systems such as Rcs and Cpx cascades are upregulated in E. coli lacking the putative lipoprotein. Additionally, Cpx signaling is required for proliferation of the mutant under restrictive conditions. Further analyses suggest that the outer membrane protein biogenesis is compromised in this mutant, implying a physiological role for this predicted lipoprotein in outer membrane protein assembly. Taken together, these results suggest that this putative lipoprotein is involved in the maintenance of cell envelope integrity.

Available for download on Tuesday, January 23, 2024

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