Members of this family (formerly, The Borrelia Oms66/Omp66 Family)are found in many Borrelia species. They are large outer membrane proteins that exhibit porin activity in planar lipid bilayers. The average single-channel conductance predicts a rather large pore diameter of 2.6 nm. The exact number of transmembrane strands is unknown but prediction methods suggest a large number, which is in agreement with the large pore. P66 may in fact form a 20–22-stranded ß-barrel structure. There is evidence that the C-terminal region may traverse through the channel and be surface-accessible. There are also indications that native P66 can elicit potent bactericidal activity and significant protective immunity against host-adapted organisms.