Acts as a flagellar brake, regulating swimming and swarming in a bis-(3'-5') cyclic diguanylic acid (c-di-GMP)-dependent manner. When bound to c-di-GMP it binds to elements of the flagellar motor (MotA (PubMed:20303158) and/or FliG and FliM (PubMed:20346719), binding to FliM also occurs in the absence of c-di-GMP), causing the motor to slow down. Thus, increasing levels of c-di-GMP lead to decreased motility. Probably binds 1 c-di-GMP dimer per subunit. Monomer (Probable). Interacts with MotA in the flagellar basal bodies (PubMed:20303158). In another study (PubMed:20346719) it was not seen to interact with MotA, but instead with FliM and FliG, also in the flagellar basal body. The N-terminal domain is involved in FliG binding, the C-terminal domain is involved in FliM binding. The PilZ domain is able to bind c-di-GMP, but with a lower affinity (dissociation constant of 1.45 uM) compared to the whole protein (dissociation constant of 0.84 uM). No visible motility phenotype. Disruption of this gene suppresses the reduced motility of a pdeH disruption, thus the double disruption is motile. Belongs to the YcgR family.