This bacterial family of proteins shows structural similarity to other pectin lyase families. Although structures from this family align with acetyl-transferases, there is no conservation of catalytic residues found. It is likely that the function is one of cell-adhesion. In PDB:3jx8, it is interesting to note that the sequence of contains several well defined sequence repeats, centred around GSG motifs defining the tight beta turn between the two sheets of the super-helix; there are 8 such repeats in the C-terminal half of the protein, which could be grouped into 4 repeats of two. It seems likely that this family belongs to the superfamily of trimeric auto-transporter adhesins (TAAs), which are important virulence factors in Gram-negative pathogens [1] [2]. In the case of Parabacteroides distasonis, which is a component of the normal distal human gut microbiota, TAA-like complexes probably modulate adherence to the host (information derived from TOPSAN).

1: The Yersinia adhesin YadA collagen-binding domain structure is a novel left-handed parallel beta-roll. Nummelin H, Merckel MC, Leo JC, Lankinen H, Skurnik M, Goldman A; EMBO J. 2004;23:701-711. PMID:14765110

2: Structure of the head of the Bartonella adhesin BadA. Szczesny P, Linke D, Ursinus A, Bar K, Schwarz H, Riess TM, Kempf VA, Lupas AN, Martin J, Zeth K; PLoS Pathog. 2008;4:e1000119. PMID:18688279