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Category: Microbial Genetics and Molecular Biology
Envelope Stress, Page 1 of 2
< Previous page | Next page > /docserver/preview/fulltext/10.1128/9781555816841/9781555816216_Chap08-1.gif /docserver/preview/fulltext/10.1128/9781555816841/9781555816216_Chap08-2.gifAbstract:
This chapter focuses on envelope stress responses of gram-negative and gram-positive bacteria. To date, five major cell envelope stress responses have been identified in Escherichia coli: the sE, Cpx, Rcs, phage-shock protein (Psp), and Bae responses. Many of stress responses in gram-positive bacteria fall into two major categories: those that are activated by directly binding the antibiotic and those that are induced by a signal generated by antibiotic action. In general, responses in the first class have small regulon encoding genes that detoxify the antibiotic by pumping it out of the cell or modifying it. This review focuses on the second class because they can be clearly defined as envelope stress responses, sensing defects in the envelope and regulating genes that alter envelope physiology to enhance survival. Even though the Bacillus subtilis LiaRS system is induced by many envelope stresses, liaRS mutants are not more susceptible to inducing stresses. σE of S. coelicolor, one of the founding members of the extracytoplasmic function (ECF) σ factor family, is one of approximately 50 putative ECF σ factors in the bacterium. Cell envelope stress responses are widespread throughout the bacterial world, but have been investigated most intensively in B. subtilis, E. coli, and their close relatives. The regulatory interactions among the key players in the response; that is, the σ/anti-σ factor and sensor kinase/response regulator pairs are highly conserved.
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Overview of the gram-positive and gram-negative cell envelopes. For the gram-negative cell envelope, the phospholipid bilayer of the inner membrane (IM) and the asymmetric bilayer with phospholipids and LPS of the outer membrane (OM) are shown with associated integral and peripheral membrane proteins and lipoproteins. The periplasm lies between the two membranes and contains the thin layer of peptidoglycan (PG). For the gram-positive cell envelope, the cytoplasmic membrane (CM) with associated proteins is shown. A thick layer of peptidoglycan (PG) lies outside of the cytoplasmic membrane. Teichoic acids (TA) are covalently attached to the peptidoglycan and lipoteichoic acids (LTA) are covalently attached to the cytoplasmic membrane. A new peptidoglycan subunit is depicted as it is being flipped across the cytoplasmic membrane prior to insertion in the mature peptidoglycan layer.
Gram-negative envelope stress responses. The key regulators, accessory proteins, and physiological inducers of the five major envelope stress responses of E. coli are shown. The flow of phosphate through the Cpx, Rcs, and Bae phosphorelay systems is indicated (P). Protease activity is indicated by scissors.
Gram-positive envelope stress responses. The key regulators and accessory proteins of the major envelope stress responses are shown. The flow of phosphate through the LiaRS and CseBC phosphorelay systems is indicated (P). Protease activity is indicated by scissors. The mechanisms that release σM and σX from their respective anti-σ factors are not known.