Characterization of Protein-Protein Interaction Within a Polyamine Responsive Signaling System in Vibrio Cholerae

The Gram-negative bacterium Vibrio cholerae is a natural inhabitant of aquatic environments and the causative agent of the severe diarrheal disease cholera. This bacterium is able to form biofilms on both abiotic and biotic surfaces. Biofilm formation is vital to the survival of V. cholerae both within aquatic reservoirs and during transmission to the human host. The bacterial second messenger cyclic-di-GMP is an important signaling system that is known to regulate biofilm formation in response to environmental signals. Previous research investigating a putative c-di-GMP-signaling pathway involving the periplasmic protein NspS and the GGDEF-EAL protein MbaA, revealed that the polyamines spermidine and norspermidine likely act as specific extracellular environmental signals to modulate NspS-MbaA interaction and affect biofilm formation. These proteins have opposite effects on biofilm formation in vitro and are encoded by adjacent genes with overlapping reading frames as part of an operon structure. The objective of this study has been to provide evidence of direct protein-protein interaction between NspS and MbaA, and to further elucidate the molecular details of the putative norspermidine/spermidine-MbaA/NspS signaling system in V. cholerae. Our results further characterize the role periplasmic polyamine-binding proteins play in cyclic-di-GMP-mediated signal transduction within the first polyamine-responsive signaling system identified in bacteria.