Porphyromonas gingivalis transports Arg-gingipains and Lys-gingipain across the outer membrane via an unknown pathway. Recently, we found that the sov gene of P. gingivalis W83 was required for this step. In the present study, we characterized the Sov protein. We constructed a P. gingivalis strain that expresses histidine-tagged Sov instead of Sov. Subcellular fractionations and a histidine-tag pulldown experiment showed that histidine-tagged Sov was present in an outer membrane fraction. Furthermore, antiserum raised against the terminal regions of Sov obstructed the secretion of Arg-gingipains from wild-type W83 cells. A deletion study showed that the region from Phe2495 to the C-terminus Gln2499 of Sov is essential for gingipain secretion. Anti-histidine-tag immunoglobulins interfered with the secretion of Arg-gingipains by P. gingivalis cells that expressed histidine-tagged Sov. In conclusion, we found that Sov is an outer membrane protein participating in the secretion of gingipains and that the C-terminal region of Sov is exposed to the extracellular milieu and involved in the modulation of Sov function.