TABLE 1.

Comparison of the channel-forming domains and the channels formed by diphtheria toxin and colicin Ia

Characteristics	Colicin Ia	Diphtheria toxin
Number of residues in channel-forming domain	∼175	∼175
Crystallographic structure of water-soluble form	10 α-helices	10 α-helices
Number of protein subunits forming the channel	1	1
Number of transmembrane segments in the channel	4 (Whole colicin) 3 (Channel-forming domain)	3
Two of the transmembrane segments are formed by hydrophobic hairpins	Yes	Yes