Functional domains of colicin M.

The structure of colicin M of Escherichia coli was studied with regard to its organization into functional domains. A proteolytic fragment with an Mr of 24,000 was isolated which comprised the carboxyterminal portion of the protein. It adsorbed to the outer membrane receptor protein and inhibited killing of cells by colicin M and by phage T5 that uses the same receptor. The fragment killed cells when the outer membrane was rendered permeable to macromolecules for a short time by the osmotic shock procedure. It is concluded that the fragment contains the receptor binding site and the active center but is lacking the sequence required for transport into cells. The carboxy-terminal amino acid sequence-Lys-Arg of the fragment was identical to that obtained from colicin M. Release of lysine and arginine led to inactivation of colicin M. The sequence of the first 39 amino acids of the amino terminal end of colicin M was determined.