Species that include Porphyromonas gingivalis, Fibrobacter succinogenes, Flavobacterium johnsoniae, Cytophaga hutchinsonii, Gramella forsetii, Prevotella intermedia, and Salinibacter ruber have on average twenty or more copies of this C-terminal domain, associated with sorting to the outer membrane and covalent modification. This domain targets proteins to type IX secretion systems and is secreted then cleaved off by a C-terminal signal peptidease [2]. Based on similarity to other families it is likely that this domain adopts an immunoglobulin like fold.

1: Protein substrates of a novel secretion system are numerous in the Bacteroidetes phylum and have in common a cleavable C-terminal secretion signal, extensive post-translational modification, and cell-surface attachment. Veith PD, Nor Muhammad NA, Dashper SG, Likic VA, Gorasia DG, Chen D, Byrne SJ, Catmull DV, Reynolds EC; J Proteome Res. 2013;12:4449-4461. PMID:24007199

2: PG0026 is the C-terminal signal peptidase of a novel secretion system of Porphyromonas gingivalis. Glew MD, Veith PD, Peng B, Chen YY, Gorasia DG, Yang Q, Slakeski N, Chen D, Moore C, Crawford S, Reynolds EC; J Biol Chem. 2012;287:24605-24617. PMID:22593568