Panel A shows the structure of the T5 receptor, FhuA, as determined by Ferguson viewed in the plane of the membrane (21). The beta-barrel traverses the outer membrane. Note the black loop that interacts with the T5 receptor binding protein pb5 (43). There is also a secondary interaction with a region within the beta-barrel. Panel B shows a “phage’s eye view” of the receptor and the cork domain which blocks the channel until the phage binds.