Proteolytic Regulation of Stress Response Pathways in Escherichia coli
Maintaining correct cellular function is a fundamental biological process for all forms of life. A critical aspect of this process is the maintenance of protein homeostasis (proteostasis) in the cell, which is largely performed by a group of proteins, ref
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Proteolytic Regulation of Stress Response Pathways in Escherichia coli Dimce Micevski and David A. Dougan
Abstract Maintaining correct cellular function is a fundamental biological process for all forms of life. A critical aspect of this process is the maintenance of protein homeostasis (proteostasis) in the cell, which is largely performed by a group of proteins, referred to as the protein quality control (PQC) network. This network of proteins, comprised of chaperones and proteases, is critical for maintaining proteostasis not only during favourable growth conditions, but also in response to stress. Indeed proteases play a crucial role in the clearance of unwanted proteins that accumulate during stress, but more importantly, in the activation of various different stress response pathways. In bacteria, the cells response to stress is usually orchestrated by a specific transcription factor (sigma factor). In Escherichia coli there are seven different sigma factors, each of which responds to a particular stress, resulting in the rapid expression of a specific set of genes. The cellular concentration of each transcription factor is tightly controlled, at the level of transcription, translation and protein stability. Here we will focus on the proteolytic regulation of two sigma factors (s32 and sS), which control the heat and general stress response pathways, respectively. This review will also briefly discuss the role proteolytic systems play in the clearance of unwanted proteins that accumulate during stress.
Introduction Like many living organisms, bacteria are constantly challenged with changing environmental conditions. In order to survive these changes, bacteria have developed a number of different cellular strategies. In cases where the stress is short-lived (e.g.
D. Micevski • D.A. Dougan (*) Department of Biochemistry, La Trobe Institute for Molecular Science (LIMS), La Trobe University, Melbourne 3086, Australia e-mail: [email protected] D.A. Dougan (ed.), Regulated Proteolysis in Microorganisms, Subcellular Biochemistry 66, DOI 10.1007/978-94-007-5940-4_5, © Springer Science+Business Media Dordrecht 2013
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heat-shock) they have developed sophisticated networks or programs to combat the effects of the stress, while in cases where the stress may be prolonged (e.g. when nutrients are depleted) they can enter a “hibernation”-like state, waiting for the return of better conditions. In fact, bacteria have developed several distinct pathways, each of which is tailored to a particular type of stress. In most cases, the response is controlled by a master regulator (or sigma factor), which in turn activates the expression of a particular set of genes (or regulon) that restore cellular homeostasis. In Escherichia coli, there are seven different sigma factors (s70, s54, s38, s32, s28, s24 and s18), all of which compete for binding to the RNA polymerase (RNAP) core enzyme, for the transcription of a specific set of genes. As such, the cellular levels of these master regula
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