Model of the potential role of pallilysin in T. pallidum dissemination.

(i) Surface-exposed pallilysin (C²⁴-P²³⁷) mediates attachment of T. pallidum (<$>\scale 60%\raster="rg1"<$>) to host components, including the laminin-rich basement membrane (BM) that underlies the endothelial cells (EC) of blood vessels and to fibrinogen/fibrin clots. The N-terminal pro-domain of pallilysin is removed via host thrombin-mediated cleavage (cleavage at S⁷⁸) or autocatalytic activation (cleavage at T⁹³), which results in release of pallilysin from the treponemal surface into the external host milieu. (ii) Released pallilysin (S⁷⁸-P²³⁷ and/or T⁹³-P²³⁷) degrades host components located in the vicinity of the disseminating treponemes, including the laminin-rich BM and fibrin clots.