PorT is a membrane-associated protein shown to be essential for the maturation and secretion of a class of cysteine proteinases, the gingipains, from the periodontal pathogen Porphyromonas gingivalis. It was previously reported that PorT is located on the periplasmic surface of the inner membrane to function as a chaperone for the maturing proteinases. In a recent report, a theoritical outer-membrane localization model, which suggested that PorT is an integral outer-membrane protein with eight anti-parallel, membrane-traversing ß-strands, was confirmed by the structural and functional tolerance of PorT to hexahistidine (6xHis) tag insertions at selected locations within the protein using site-directed mutagenesis. PorT homologues have been found in restricted members of the Bacteroidetes phylum where there is potential for PorT to participate in the maturation and secretion of proteins with characteristic C-terminal domains (CTDs).