High-affinity cyclic-di-GMP binding protein that regulates type IV pili (T4P) elongation. Required for T4P-mediated surface attachment and walking motility during the early phases of surface colonization. Not required for twitching motility. Does not bind related nucleotides such as GMP, GDP, GTP or ATP. Monomer in the absence of c-di-GMP. Forms dimers in the presence of c-di-GMP. Rapidly localizes to the cell poles upon surface contact in a c-di-GMP-dependent manner. Dynamically transitions between the cytoplasm and the cell poles, as a function of c-di-GMP binding. Contains a PilZ-like fold that binds two molecules of c-di-GMP via two well-conserved c-di-GMP-binding motifs, RXXXR and D/NXSXXG. Mutant has reduced surface piliation and is unable to increase piliation upon surface exposure. It shows defects in initial surface attachment and in early biofilm formation, but late biofilm formation is not affected. Mutant loses walking motility but twitching motility is barely affected. Truncated N-terminus.