The Treponema pallidum protein, Tp0751 (also known as pallilysin), possesses adhesive properties and has been previously reported to mediate attachment to the host extracellular matrix components laminin, fibronectin, and fibrinogen. Tp0751 adopts an eight-stranded beta-barrel with a profile of short conserved regions consistent with a non-canonical lipocalin fold. Lipocalins, along with fatty acid-binding proteins and avidins, are members of the calycin superfamily, which is defined by the distinct features of a central beta-barrel and a key structural signature consisting of three short conserved regions (SCR1, SCR2, and SCR3). However, Tp0751 does not contain all three conserved regions, hence it is considered an outlier to canonical lipocalins. In SCR1, there is a GxW motif [1].

1: The Structure of Treponema pallidum Tp0751 (Pallilysin) Reveals a Non-canonical Lipocalin Fold That Mediates Adhesion to Extracellular Matrix Components and Interactions with Host Cells. Parker ML, Houston S, Petrosova H, Lithgow KV, Hof R, Wetherell C, Kao WC, Lin YP, Moriarty TJ, Ebady R, Cameron CE, Boulanger MJ; PLoS Pathog. 2016;12:e1005919. PMID:27683203