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Mutational analysis supports a role for multiple structural features in the C ‐terminal secretion signal of Escherichia coli haemolysin
Author(s) -
Stanley P.,
Koronakis V.,
Hughes C.
Publication year - 1991
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1991.tb02085.x
Subject(s) - biology , escherichia coli , secretion , genetics , hemolysin , terminal (telecommunication) , escherichia coli proteins , computational biology , microbiology and biotechnology , gene , virulence , biochemistry , telecommunications , computer science
Summary We have carried out an extensive mutational analysis of the C ‐terminal signal which targets the export of the 1024‐residue haemolysin protein (HlyA) of Escherichia coli across both bacterial membranes into the surrounding medium. Over 60 variants of the HlyA C ‐terminal 53‐amino‐acid sequence were created by oligonucleotide‐directed mutagenesis and fused to the HlyA N‐terminal 830 residues. Transport of the HlyA derivatives by the HlyB/HlyO system was compared with the wild‐type level and the data indicate that the HlyA C ‐terminal export signal lies within the last 48 amino acids and comprises three functional domains: an amphipathic, charged helix between residues 1,977 and R,996; a 13‐amino‐acid uncharged region from residue T,997 to S,1009; and an 8‐aminoacid hydroxylated tail at the extreme C ‐terminus. Analogous features were found in the C ‐terminal sequences of an extended family of haemolysins, leukotoxins and proteases which are secreted by HlyB/HlyD‐type translocators. In particular, all nine proteins which are secreted into the extracellular medium possess potential extended amphipathic helices. These results suggest a possible role for multiple regions of the HlyA C ‐terminal export signal in which the first two domains span the membranes and the third domain remains in the cytoplasm.