Pseudomonas aeruginosaAlgF is a protein-protein interaction mediator required for acetylation of the alginate exopolysaccharide

Abstract

ABSTRACTEnzymatic modifications of bacterial exopolysaccharides enhance immune evasion and persistence during infection. In the Gram-negative opportunistic pathogenPseudomonas aeruginosa, acetylation of alginate reduces opsonic killing by phagocytes and improves reactive oxygen species scavenging. Although it is well-known that alginate acetylation inP. aeruginosarequires AlgI, AlgJ, AlgF, and AlgX, how these proteins coordinate polymer modification at a molecular level remains unclear. Here, we describe the structural characterization of AlgF and its protein interaction network. We characterize direct interactions between AlgF and both AlgJ and AlgXin vitro, and demonstrate an association between AlgF and AlgX, as well as AlgJ and AlgI, inP. aeruginosa. We determine that AlgF does not exhibit acetylesterase activity and is unable to bind to polymannuronatein vitro.Therefore, we propose that AlgF functions to mediate protein-protein interactions between alginate acetylation enzymes, forming the periplasmic AlgJFXK (AlgJ-AlgF-AlgX-AlgK) acetylation and export complex required for robust biofilm formation.