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Biogenesis of the Escherichia coli haemolysin toxin
Author(s) -
Koronakis
Publication year - 1998
Publication title -
journal of applied microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.889
H-Index - 156
eISSN - 1365-2672
pISSN - 1364-5072
DOI - 10.1046/j.1365-2672.1998.0840s1151s.x
Subject(s) - escherichia coli , toxin , microbiology and biotechnology , hemolysin , biology , biogenesis , enterobacteriaceae , microbial toxins , bacteria , genetics , virulence , gene
The synthesis, maturation and export of haemolysin by Escherichia coli are each remarkable mechanisms. Transcription of the hlyCABD operon is dependent upon a short 5′ operon polarity suppressor (ops) element and the NusG‐related RfaH protein, which in‐vitro transcription studies show act together to determine a novel regulatory mechanism that suppresses transcription polarity. Other in‐vitro studies have revealed an apparently unique acylACP‐dependent fatty acylation mechanism underlying the cytosolic maturation of the protoxin proA, with the HlyC acyltransferase binding two independent, two‐protoxin recognition domains spanning the two‐target lysine residues that are fatty acylated. Both events are required for toxin action on the host target cell. Haemolysin secretion is an ‘all or nothing’ process directed by the HlyA uncleaved C‐terminal signal and requiring both ATP hydrolysis and total proton motive force. Translocation generates no periplasmic intermediate, suggesting that the secretion machinery comprising HlyB, HlyD and TolC, must interact to form a complex to span both membranes, and if this is so, one might suppose that the large haemolysin polypeptide traverses the outer membrane through a TolC pore. The two‐dimensional TolC structure was obtained by image processing of electron micrographs of TolC ordered arrays in reconstituted lipid bilayers. This structural approach and study of close interactions between the three translocator proteins is allowing a better view of the export machinery.