The Treponema Major Surface Protein is a rather large protein acting as a surface antigen in the outer sheath of Treponema denticola. It is mainly an adhesin, but it has also been showed to exhibit channel activity. The channel is estimated to have a pore diameter of 3.4 nm and prediction methods suggest that the protein possesses a transmembrane domain. Homologs are also found in other pathogenic species of Treponema. However, the ß-barrel domain may be considerably shorter than predicted, since a large portion of the N-terminal is shown to be surface-exposed and associated with antigenicity.