The domains of the pore-forming protein responsible for the gate and channel formations were separated and identified in the outer membrane of Pseudomonas aeruginosa. The proteolytic cleavage of the 46K channel protein, protein D2, yielded two major domains with apparent M r of 27K and 19K. We identified the 27K polypeptide to be the channel-forming domain by an in vitro permeability assay. The channel size of purified 27K domain was indistinguishable from that of native protein D2. Degradation of the 19K domain into small subfragments increases the channel activity about ten times suggesting that the 19K polypeptide forms the gate or cap.
