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).
References:
The pellicle exporting porin of 1193 aas and 1 N-terminal α-helical TMS with up to 48 β-strands, PelB. The porin is in the N-terminal domain while the 19 predicted periplasmic TPRs are C-terminal. These repeats bind PelA, a periplasmic hydrolase (see the family description and Marmont et al. 2017). PelA and PelB together form a modification and secretion complex essential for Pel polysaccharide-dependent biofilm formation in P. aeruginosa (Marmont et al. 2017).
PelB of Pseudomonas aeruginosa
Extracellular Matrix protein, PelB, of 1332 aas and 2 TMSs, one N-terminal and one C-terminal.
UP of Ralstonia solanacearum
Biofilm formation protein, PelB, of ``59 aas and 1 N-terminal TMS and possibly a second near the C-terminus.
of Alishewanella agri
Tetratricopeptide repeat-containing protein, TPR_4, of 900 aas and 1 N-terminal TMS.
TPR_4 of Nitrosospira multiformis
Uncharacterized protein of 1278 aas and 1 N-terminal TMS plus 1 possible C-terminal TMS.
UP of Delftia acidovorans
Uncharacterized protein of 1025 aas and 1 N-terminal TMS and possibly one C-terminal TMS.
UP of Marinobacter vinifirmus