Might be involved in ligand transport, alters membrane permeability at acidic pH (4.0 to 5.5) (PubMed:21965687). Incubation of the non-lipidated form with lipid vesicles increases their permeability (PubMed:16159783). A mix of monomer and dimers; may integrate into the membrane as a dimer. An amphitropic protein able to integrate into the inner leaflet of the outer membrane, probably via amphipathic helices 7 and 8 (PubMed:21965687). It has no surface-exposed domains (PubMed:16159783). Forms a U-shaped beta-half-barrel with a large hydrophobic cavity (3549 Angstroms(3)). The cavity is opened when amphipathic helices 2, 3 and 9 move away from helices 7 and 8 (PubMed:21965687). Has 5 potential amphipathic helices (P1 to P5, residues 56 to 63, 155 to 162, 194 to 202, 240 to 250, and 270 to 279 respectively); P2, P3 and P5 form helices in the presence of lipid vesicles (PubMed:16159783). Palmitoylated upon expression of a fusion protein with first 46 residues fused to PhoA in E.coli. Recognized by sera from 43/43 syphilis patients, it shows promise as a diagnostic antigen (PubMed:12904373). In diagnostic tests for syphilis this protein exhibits a sensitivity of 98% and a specificity of 100%. A fusion with TP0453 (residues 32-287 of TP0453 fused N-terminally to residues 38-450 of TP0326) exhibits a sensitivity of 98% and a specificity of 99%, and both proteins exhibit superior accuracy in classifying analytical false-positive samples than a commericially available test, making them candiates for diagnosis (PubMed:23100335).