1.B.85.  The Pellicle Polysaccharide Export Porin (PelB) Family  

The pellicle (PEL) polysaccharide is synthesized by the opportunistic pathogen Pseudomonas aeruginosa and is an important biofilm constituent, critical for bacterial virulence and persistence. PEL is a cationic polymer that promotes cell-cell interactions within the biofilm matrix through electrostatic interactions with extracellular DNA. Translocation of PEL across the outer membrane probably occurs via PelB, a membrane-embedded porin with a large periplasmic domain predicted to contain 19 tetratricopeptide repeats (TPRs). TPR-containing domains are typically involved in protein-protein interactions which might serve as a periplasmic scaffold to recruits other components of the PEL secretion apparatus. Marmont et al. 2017 showed that the TPR domain of PelB interacts with PelA, an enzyme with PEL deacetylase and hydrolase activities. Repeats 9-14, which are required for the cellular localization of PelA with PelB are also essential for PEL-dependent biofilm formation. The interaction between PelA and PelB is direct, and the deacetylase activity of PelA increases as its hydrolase activity decreases when these proteins interact. Thus, the TPR-containing domain of PelB localizes PelA to the PEL secretion apparatus within the periplasm, and this may allow for efficient deacetylation of PEL before it is exported from the cell (Marmont et al. 2017).