Rendering a membrane protein soluble in water: a common packing motif in bacterial protein toxins.

The recently determined structures of three different protein toxins by X-ray crystallography has unexpectedly revealed a common membrane-insertion domain. This domain consists of an alpha-helical bundle of between seven and ten helices, some of which are hydrophobic. The three toxins, colicin, insecticidal delta-endotoxin and diphtheria toxin are directed towards different hosts, have different killing mechanisms and bear no sequence homology. The observation of a common membrane-insertion domain has implications for the design of therapeutic agents in combating disease.