Alterations of amino acid repeats in the Escherichia coli hemolysin affect cytolytic activity and secretion.

The primary structure of the Escherichia coli hemolysin polypeptide (HlyA) is used to predict intramolecular structures involved in the secretion and cytolytic activity of the molecule. The C-terminal region of HlyA contains a repeated, 8-amino acid chain represented by the consensus sequence Leu-Xaa-Gly-Gly-Xaa-Gly-Asn-Asp. Three in vitro derived mutations of hlyA are described that encode molecules missing various portions of the C-terminal region, including the repeat region. The wild-type and mutated HlyA molecules were analyzed for the ability to be secreted and to lyse erythrocytes. Hemolytic activity absolutely requires the presence of the repeats. The ability of the mutated HlyA molecules to initiate membrane translocation and be secreted required the presence of the C terminus and, to a degree, the repeated amino acid octets.