Bis-(39-59) cyclic dimeric guanosine monophosphate (c-d-GMP) is a monocyclic RNA dinucleotide controlling biofilm formation via a transmembrane receptor LapD, a periplasmic cysteine protease LapG, and surface adhesin protein LapA depending on the level of phosphate in the medium. When the phosphate level is low, LapD is held in the off state by interactions of their EAL domain, with the S helix and the GGDEF domain, which allows the proteolytic reaction of LapA on the cell surface, and consequently biofilm dispersal. Interaction of c-d-GMP to the phosphodiesterase binding site on the EAL domain is required to stimulate the receptor (LapD) to release the S helix and the GGDEF domain facilitating the formation of a trans-subunit dimer interface, the binding of LapG to the output domain of LapD, and consequently permitting the activation of LapA to form biofilm.